The Monetary Value of the Soft
Benefits of Green Roofs
FinalReport
Prepared by:
Ray Tomalty, Ph.D.
and
Bartek Komorowski, MUP
with the assistance of Dany Doiron
SmartCitiesResearchServices,Montreal
Prepared for:
CanadaMortgageandHousingCorporation(CMHC)
August, 2010
1
Acknowledgements
The authors would like to thank the following project advisors for their invaluable
guidance in conducting this study: Hitesh Doshi (Ryerson University), Jamie Meil
(Athena Institute), Steven Peck (Green Roofs for Healthy Cities), Douglas Pollard
(CMHC), and Ralph Velasquez (Tremco Inc.).
2
TableofContents
1 Introduction.........................................................................................................................i
2 ValuationMethodologies.................................................................................................i
3 ValuationofBenefits........................................................................................................ii
PropertyValues...................................................................................................................................ii
MarketingBenefits............................................................................................................................vi
FoodProductionandFoodSecurity..........................................................................................vii
SoundAttenuation..........................................................................................................................vii
StormwaterRetention.....................................................................................................................ix
AirQuality.............................................................................................................................................x
GHGSequestration............................................................................................................................xi
4 CaseStudies.....................................................................................................................xiii
901CherryAvenue,SanBruno,CA...........................................................................................xiii
FairmontWaterfrontHotel,Vancouver,BC..........................................................................xiii
401Richmond,Toronto,ON.......................................................................................................xiv
RooftopVictoryGardens,Chicago,IL......................................................................................xiv
TheLouisa,Portland,OR................................................................................................................xv
5 Conclusions........................................................................................................................xv
Bibliography............................................................................................................................xix
1 Introduction........................................................................................................................1
2 ValuationMethodologies................................................................................................3
2.1
2.2
2.3
RevealedPreferenceMethodologies................................................................................4
StatedPreferenceMethodologies......................................................................................5
AvoidedCostMethodologies...............................................................................................6
3 ValuationofBenefits........................................................................................................8
3.1
3.2
3.3
3.4
3.5
3.6
3.7
Propertyvalueincrease........................................................................................................9
Marketing................................................................................................................................16
Foodproductionandfoodsecurity................................................................................20
SoundAttenuation................................................................................................................24
StormwaterRetention........................................................................................................27
AirQualityImprovement...................................................................................................32
GreenhouseGasSequestration........................................................................................36
4 CaseStudies......................................................................................................................40
4.1
4.2
4.3
4.4
4.5
CaseStudy1–901CherryAvenue,SanBruno,CA...................................................42
CaseStudy2–FairmontWaterfrontHotel,Vancouver,BC...................................49
CaseStudy3–401Richmond,Toronto,ON................................................................56
CaseStudy4–RooftopVictoryGardens,Chicago,IL...............................................64
CaseStudy5–TheLouisa,Portland,OR......................................................................72
5 Conclusions.......................................................................................................................80
3
Interviewees............................................................................................................................84
Bibliography............................................................................................................................86
4
Summary
1 Introduction The use of green roofs can offer a tangible solution to many challenges faced by
communities across Canada today. Articulating the value of those benefits in
monetary terms provides an estimate of their contribution to local and regional
economies and permits governments, land developers and building owners to
assess short- and long-term public and private gains.
While some benefits are directly measurable and have ‘hard’ values (such as the
energy savings due the insulation provided by the soil and vegetation of a green
roof), many benefits are not readily measurable and their values are difficult to
estimate (such as the health benefits of a rooftop garden). For the purpose of this
study, those benefits that are not directly measurable (or calculated based on any
line item on the buildings budget) will be defined as ‘soft’ benefits.
The purpose of this report is to provide methodologies and case studies that can
offer guidance in attributing economic value to selected soft benefits of green roofs.
We offer methodologies that can be easily employed by stakeholders with limited
information about the property concerned. In other words, our goal is to put
forward heuristic methods that can be used with data that is usually readily at hand.
Needless to say, this approach entails a trade-off between ease of use and the level
of detail and precision. Keeping this in mind, the results obtained with the proposed
methods should be applied prudently.
2 Valuation Methodologies The soft benefits of green roofs are not directly tradable and therefore do not have
directly measurable monetary values. To determine their monetary value, nonmarket or indirect valuation techniques must be employed. Estimating the total
economic value of a non-market good or service entails calculating the sum of all
values associated with that good or service. The two main categories of value are
use and non-use values. Use values can either be direct or indirect. Direct use value
refers to the value that is derived from actual or planned use of a particular
environmental service or good. Recreation and food production are two examples of
direct use values. Indirect use value occurs when people benefit from an
environmental amenity without consciously using it. Water filtration, climate
regulation are examples of the indirect use values of environmental amenities. Non-
use value refers to the value that individuals place on an environmental amenity
without having any planned use for it. An example of a non-use value is the intrinsic
value that people attribute to an environmental amenity (like the boreal forest)
simply for its existence. The methods used to estimate non-use values are
considerably more complex and are beyond the scope of this report.
Non-market valuation techniques have been developed in order to estimate the net
value that the public or individuals attribute to environmental amenities such as
green infrastructure. Three general categories of nonmarket valuation
methodologies exist. The first category,revealed preference methods (i.e., travel
cost, hedonic pricing, market comparables, and cost avoidance) uses behaviours and
information observed in markets to estimate non-market values. The second
category, stated preference methods, which includes the contingent valuation
technique, attributes economic value by asking people their willingness to pay for a
service or willingness to accept compensation to voluntarily forgo a service. The
third category is avoided cost analysis, which can be used to determine the value of
green infrastructure by quantifying the costs that would be incurred if the services
provided by the infrastructure were not available or had to be provided by building
conventional infrastructure.
3 Valuation of Benefits The objective of our research is to provide readers with non-technical methods for
estimating the soft benefits associated with a green roof project based on readilyavailable information and without the need for undertaking major research. The
benefits that are included here are those for which we could find relatively simple
valuation methods that could be applied by non-specialists with limited resources
for data gathering. The proposed methods were gathered from current practices
and the existing literature.
Property Values Green infrastructure investments have been shown to positively affect the property
value and marketability of nearby real estate. In the case of green roofs, this benefit
would accrue to the owner or owners of a building with a green roof and, to a lesser
degree, to owners of surrounding properties. Hedonic valuation techniques have
been used to measure the relationship between the selling price of a residence and
its distance from an urban greenspace, park, community garden or wetland. At
present, there are no studies that have measured the potential of green roofs to
increase the selling price of a condominium or other residential building. In the
absence of hedonic pricing studies looking specifically at green roofs, we can use
estimates of property value increases generated by other types of green
infrastructure, e.g., an at-grade community garden or park.
ii
View onto a Green Roof Assuming that having a view onto a green roof has a similar effect to new tree
plantings, the value of the benefit accrued to owners of properties is 9% of the value
of the portion of a building that affords a direct view onto a green roof. This is based
on Wachter’s (2004) finding that tree planting along a street in front of a property
increases the property's value by up to 9%. Where neighbours of the green rooftop
are concerned, we assume that greening a rooftop is equivalent to tree planting atgrade – it adds greenery but does not change the amount of recreational green space
to which they have access. We do not attribute any increased value to a green roof
without trees.
Assuming that having a view onto a green roof has a similar effect to new tree
plantings, the value of the benefit accrued to owners of properties is 9% of the value
of the portion of a building that affords a direct view onto a green roof. This is based
on Wachter’s (2004) finding that tree planting increases property values up to 9%.
Where neighbours of the green rooftop are concerned, we assume that greening a
rooftop is equivalent to tree planting at-grade. For them, the greening of the rooftop
has much the same effect as tree planting – it adds greenery but does not change the
amount of green space to which they have access. We do not attribute any increased
value to a green roof without trees.
For the purpose of estimating the value of the benefit for a wholebuilding, we
assume that only half the neighbouring storeys above the green roof are oriented so
as to afford a view onto it. The increase in property value that accrues to a building
with a view onto a green roof can therefore be estimated using the following
formula:
1 h −h
⋅ vv
b = 0.09⋅ ⋅ v
2 hv
= 0.045⋅
hv − h
⋅ vv
hv
Where:
•
b = value of benefit ($)
•
vv= value of neighbouring property with a view onto the green roof
($)
•
h = height of the green roof host building (storeys)
•
hv = height of the building with a view onto the green roof (storeys)
For the purpose of estimating the value of the benefit for a singleunit in a building
that has a direct view onto a green roof, we propose using the following formula:
iii
oftop Garden
n Recreeational Roo
A roo
oftop garden
n that is acccessible to building
b
dweellers will o
offer recreattional
beneefits that maay be reflectted in the vaalue placed on the build
ding. To estimate this
valuee, we turn to
o studies that have asseessed the im
mpact on ho
ousing valuees in
locattions abuttin
ng public paarks. Using the hedonicc method, C
Crompton (2
2005) has
suggested that homes
h
adjaccent to public parks havve about a 2
20% higher property
d
from
m parks.. Givven that an aabutting paark offers
valuees than simiilar homes distant
both recreationaal and view benefits, we deduct the view beneefit (9% of p
property
valuee) calculated
d above to arrive
a
at a recreational benefit of 1
11%.
We propose
p
the increase in property value yielded
d by a recreeational rooftop garden
n
be esstimated usiing the follo
owing formu
ula:
b = 0.11⋅ v
Wherre:
•
b = value of th
he benefit ($)
•
v = value of th
he green roo
of host prop
perty ($)
Produ
uctive Roofto
op Garden Assuming that having
h
a pro
oductive roo
oftop garden
n is tantamo
ount to abuttting an atgradee communitty garden, we
w propose that the vallue of the lo
ong-term benefit
accru
ued to the owner of thee property be
b estimated
d at 7% of th
he value of the
property. This iss based on Voicu
V
and Been’s (2008
8) finding th
hat, on averaage,
y gardens in
ncreased in vvalue by 7.4
4% by five
properties abuttting typical community
yearss after the construction
c
n of the gard
den. As we d
do not know
w from thesee findings
whatt the effect is in the longger term, we
w assume th
he value rem
mains consttant at the
five-y
year level.
We propose
p
the increase in property value yielded
d by a privaate, productive rooftop
gardeen be estimated using the
t followin
ng formula:
Wherre:
•
b
($)
b = value of benefit
•
v = value of grreen roof ho
ost propertyy ($)
iiv
If thee productivee rooftop gaarden is opeen to non-occcupants of the building then it is
moree likely that benefits wiill accrue to owners of n
neighbourin
ng properties. In this
case, we assumee that the ro
ooftop gardeen behaves exactly likee an at-gradee
comm
munity gard
den. In the lo
ong-term, th
he value of tthe benefit accrued to
neigh
hbouring prroperty own
ners is 7% for
f owners iin the buildiing with thee rooftop
comm
munity gard
den and the immediate vicinity of tthe host buiilding, 5% ffor those up
to 50
00 feet away
y, and 2% fo
or those up to
t 1,000 feeet away. Agaain, the valu
ues are
based
d on Voicu and
a Been (2
2008) and assumed to h
hold at theirr five-year llevel.
We propose
p
the increase in property value accrueed to a neigh
hbouring prroperty of a
publiicly accessib
ble productive rooftop garden be eestimated u
using the folllowing
form
mula:
Wherre:
•
b = value of benefit
b
($)
•
v = property value
v
($)
•
d = distance from
f
green roof
r
host prroperty (meeters)
•
F= distance factor
f
(functtion of d)
•
F = 0.07 when
n0≤d≤5m
•
F = 0.05 when
n 5 m < d ≤ 150 m
•
n 150 m < d ≤ 300 m
F = 0.02 when
•
F= 0 when d > 300 m
Let:
Area‐‐Wide Beneffit The above
a
stated
d formulas are
a intendeed for calculating the vaalue of proxximity
beneefits that acccrue to indiv
vidual properties. Mun icipal decision makers may be
moree interested
d in the totall, area-widee increase in
n property vvalues resullting from a
green
n roof projeect. In this caase, it is neccessary to su
um the valu
ues of the beenefit
accru
uing to the host
h
properrty with thosse accruing to neighbouring propeerties.
Wherre:
v
•
btootal = total arrea-wide prroperty valu
ue benefit ($$)
•
bn = property
y value beneefit of an ind
dividual pro
operty ($)
Marketing Ben
nefits The mass
m
mediaa and the pu
ublic’s intereest in enviroonmentally friendly pro
oducts and
serviices continu
ue to rapidly
y increase in
n North America. Green
n roofs and other green
n
infrastructure on or near a building can
n therefore be considered as a maarketing
nity that inccreases a deevelopment’’s exposure and enhancces the abso
orption ratee
amen
of itss units. Appllying the comparable co
osts method
dology, one way of estiimating the
mark
keting beneffits of green
n infrastructture would be to assesss the value o
of the
publiicity gained
d as a direct consequencce of green infrastructu
ure investm
ments.
The marketing
m
benefits
b
of green
g
roofs will
w depend
d on a numb
ber of factorrs that are
unkn
nown in adv
vance or diffficult to quaantify, such aas the curreent interest of local
mediia in green infrastructu
i
ure and greeen buildingss. The best w
way to estim
mate the
mark
keting beneffits is by bassing it on th
he value of tthe publicityy received d
due to the
preseence of the green
g
roof in
i the project. The valu
ue of the freee publicity rreceived can
n
be esstimated by comparison
n to the cost of advertizzing in threee media: raadio,
telev
vision, and print.
p
The co
ost for each of the threee media is b
broken down
n into the
production cost plus the cost of runnin
ng the ad. Th
he former caan be assum
med to be
consttant as it is a onetime cost.
c
The lattter is the coost of havingg the ad aireed on radio
and television
t
an
nd printed in
i newspapers.
The value
v
of freee publicity can
c in principle be estim
mated accorrding to thee following
form
mula:
Wherre:
•
he benefit ($)
b = value of th
•
pradio
= radio ad
a productiion cost ($)
r
•
rraadio = radio ad
a running cost
c
(airtim
me) ($/30s sspot)
•
traadio = total raadio equivalent airtimee (30s spotss)*
•
ptvv = tv ad pro
oduction cost ($)
•
rtvv = tv ad run
nning cost (aairtime) ($//30s spot)*
•
ttvv= total tv equivalent airtime (30s spots)
vvi
•
ppaper
= newsp
paper ad production coost ($)
p
•
rpaaper = newsp
paper ad run
nning cost ((printing) ($$/column in
nch)
•
l = total equiv
valent colum
mn length (ccolumn inch
hes)
* Totaal airtime is divided by 30 to
o convert to number of spotts.
Food
d Production and Food Securitty Green roofs and at-grade gaardens can provide
p
imp
portant opp
portunities ffor healthy
food production
n. Rooftop an
nd commun
nity gardenss can help m
meet nutritio
onal
requirements an
nd reduce household exxpendituress on food wh
hile encouraging
stew
wardship of land
l
by site users. Urbaan agricultu
ure can provvide city-dw
wellers with a
sourcce of fresh produce,
p
improved diett and imporrtant househ
hold budgettary savingss.
Comb
bining averaage garden plot yields and cost savvings from tthe purchasse of
produce (based on market prices)
p
can help us evaaluate the m
monetary vallue of urban
n
food production
n.
From
m our review
w of existingg urban gard
dens, we esttimate that their produ
uctivity
rangees between $20,000 an
nd $200,000
0 per hectarre per growiing month. It appears
that mixed
m
fruit and vegetab
ble gardenss are at the llow end of tthe producttivity range
whilee gardens fo
ocused more on flowers, herbs, an d lettuces aare at the higgher end.
The productivity
p
y of an urbaan garden allso dependss on the durration of thee growing
seaso
on – i.e., the number of months bettween the laast spring frrost and thee first fall
frost.
We propose
p
the value of thee food production beneefit be estim
mated using the
follow
wing formu
ula:
Wherre:
•
b = annual vaalue of benefit ($/year)
•
g = duration of
o the growing season ((months)
•
P = productiv
vity ($/m2•m
month)
•
a = green roo
of area (m2)
Soun
nd Attenua
ation Vegeetated surfacces provide important sound insullation propeerties and aare often
emplloyed for their noise reduction pottential in urrban settinggs. Green roo
ofs can
provide importaant noise red
duction opp
portunities ffor buildinggs, especially those
vvii
undeer flight path
hs or elevatted transit systems. Hed
donic pricin
ng and contiingent
valuaation metho
odologies haave both beeen employeed to assess the social ccosts of noisse
and estimate
e
vallues for noisse reduction
n measuress such as greeen roof
impleementation.
Soun
nd attenuation provided
d by a green
n roof will d
depend on th
he properties of the
choseen substrate and on thee substrate’’s thickness . In the abseence of dataa on the
noisee attenuatio
on propertiees of differen
nt substratees with diffeerent thickn
nesses, we
propose a low (5
5 dB attenuation) and a high scenaario (13 dB attenuation
n) based on
Conn
nelly & Hodg
gson’s (2008) findings on the soun
nd attenuatiion of 75 mm
m and 150
mm green
g
roof substrates.
s
The
T aforementioned fin
ndings are tthose for low
w- and mid-rangee frequenciees; we assum
me that most ambient noise in an urban setting falls into
o
this category.
c
We
W assume th
hat a green roof would primarily rreduce noisees from
overh
head sourcees, such air traffic
t
and elevated
e
roaadways and
d trains; it w
would have
little or no effectt on street level traffic noise. Thuss, the benefit would onlly accrue to
properties affectted by overhead noise.
When
n using the hedonic priicing technique, the cosst of noise iss measured
d by the
Noisee Sensitivity
y Depreciatiion Index (N
NSDI), which representts the averaage
perceentage decrrease in totaal property value
v
per 1--decibel inccrease in noise level
abov
ve a baselinee level. Baseed on the fin
ndings of Baateman et all (2000), forr propertiess
near airports or under airport flight paaths, we proopose using an NSDI of 0.33%; for
properties near elevated ro
oadways or railways
r
thaat are abovee roof level,, we proposse
using
g an NSDI off 0.64%.
We assume
a
that a green roo
of would only affect noiise levels on
nly on the to
op floor of
the building.
b
Forr the purposse of estimaation, we asssume that eeach floor iss worth an
equaal portion off the total prroperty valu
ue. Hence, th
he value of the top floo
or is the totaal
property value divided
d
by the
t number of storeys.
p
the value of thee sound atteenuation beenefit be esttimated usin
ng the
We propose
follow
wing formu
ula:
Wherre:
•
b
($/yeear)
b = value of benefit
•
d
n index (/d
dB)
NSSDI = noise sensitivity depreciatio
•
n = green roo
of sound atteenuation (d
dB)
•
h = building height
h
(storeys)
•
v=
= property value
v
($)
viiii
Using
g the valuess given abov
ve for the low attenuatiion scenario
o and for airr traffic, we
obtaiin:
b = (0
0.0033 dB)⋅ (5dB)⋅
= 0.0165⋅
0
v
h
v
h
Stormwater Re
etention Vegeetated surfacces on roofttops can rettain consideerable amou
unts of storm
mwater and
d
reduce peak flow
ws into the stormwater
s
r system during storm events. Lesss peak
runoff means that new storm sewer sy
ystems can h
have a smalller capacityy or existingg
systeems can sup
pport more developmen
d
nt before beeing upgrad
ded, which trranslates to
o
lower capital exp
penditures for develop
pers and mu
unicipalitiess. Lower peaak flows
mean
ns lower exp
penditures by the municipality in erosion con
ntrol measu
ures along
streaams and riveers. Thus, we
w propose that
t
the ben
nefit of this m
measure bee estimated
by caalculating th
he avoided cost
c
of expanding storm
mwater treaatment facilities and in
erosiion control measures.
For the
t stormwaater retentio
on benefit, Cunningham
C
m (2001) prrovides figu
ures for the
cost of
o three typ
pes of storm
mwater reten
ntion infrasttructure, including: a surface
storm
m water reteention pond
d, valuated at
a $20.13/m
m3 of stormw
water; mixeed at-grade
BMPs, valuated at $212.15//m3 of storm
mwater; and
d an undergground reten
ntion basin,,
3
nefit, the Cityy of
valuaated at $1,059.44/m of stormwateer. For the eerosion ben
Wateerloo (2005) estimates that conven
ntional storrmwater maanagement
infrastructure reelated to ero
osion control requires a one-time expenditurre of
3.66/m3 of stormwater..
C$13
The values
v
per unit
u of area of the green
n roof of thee stormwateer services tthat we are
consiidering depend criticallly on the waater retentiion capacityy of the greeen roof. For
estim
mation purposes, we wiill assume an
a average rretention caapacity of 42
2.7L/m2roof,
as ussed by Carteer and Keeleer (2008), which
w
we takke to be a tyypical figuree for an
exten
nsive green roof.
We propose
p
the value of thee storm watter retention
n benefit bee estimated using the
follow
wing equatiion:
Wherre:
•
b
($)
b = value of benefit
iix
•
R = stormwatter retention
n cost ($/m
m3water)
•
E = erosion mitigation
m
co
ost ($/m3watter)
•
C= average green
g
roof reetention cap
pacity (m3waater/m2roof)
•
a = green roo
of area (m2rooof)
Using
g the valuess for stormw
water retenttion cost (foor the cheap
pest alternative, a
reten
ntion pond) and erosion
n mitigation
n cost given
n above, we get:
Air Q
Quality Green plants abssorb gaseou
us pollutantts through th
heir leaf sto
omates (porres).
Vegeetations can also capturre some of th
he particulaate matter in the air. Byy mitigatingg
the heat
h
island effect,
e
urban
n vegetation
n can furtheer help reduce smog givven that
higheer temperattures favourr smog form
mation. Air p
pollution ad
dds to the bu
urden of thee
healtth care systeem, causes disabilities
d
or prematu
ure death, an
nd reduces tthe
productivity of the
t workforrce. In orderr to assess th
he economiic value of this service,
we caan estimatee the avoided cost of health care.
The critical
c
deteerminants of a green roof’s capacitty to mitigatte pollution and yield
healtth benefits include its area
a
and thee mix of plan
nt species th
hat is used, as some
speciies absorb more
m
pollutaants than otthers. Otherr factors incclude the levvels of air
pollu
ution at the given
g
locatiion and the climate. In tterms of thee latter, the pollution
mitig
gation proviided by the green roof may
m be limiited outsidee the growin
ng season,
partiicularly if it is covered with
w snow. We
W take a sseven-month
h growing sseason to bee
the baseline
b
casee.
We have
h
calculated values for
f the pollu
utant removval health beenefit usingg Yang, Yu
and Gong’s
G
(200
08) and Kow
wal’s (2008)) findings (ssee Table S-1).
Table
e S‐1 ‐ Value
e of annual p
pollutant rem
moval healtth benefit fo
or different ttypes of 2
green
n roof vegettation (US$//m ∙year) Type o
of vegetation SO2 N02 PM
M10 O3 Total x
Short G
Grass Tall He
erbaceous Plantss Decidu
uous Trees 0..0010725 0..0013695 0..0016665 0.0157275 0.0198450 0.0240975 0.00504 0.00684 0.00972 0.0303075 0.0392175 0.0483975 0.05221 0.06773 0.08339 Combining data from Yang, Yu an
nd Gong (2008
8) and Kowal (2008)
We propose
p
the following fo
ormula for estimating
e
tthe annual vvalue of thee health
beneefit of pollution mitigatiion provided by green rroofs:
Wherre:
•
b = value of benefit
b
($/yeear)
•
g = growing season
s
(mon
nths)
•
Hsg
b
for sh
hort grass p
pollution ab
bsorption ($
$/m2•year)
s = health benefit
•
asgg = green ro
oof area cov
vered by shoort grass (m
m2)
•
Htg
b
for taall grass* poollution abssorption ($//m2•year)
t = health benefit
•
atgg = green ro
oof area covered by talll grass* (m2)
•
Hd = health beenefit for deeciduous plaant pollutio
on absorptio
on
($
$/m2•year)
•
ad = green roo
of area coveered by deciiduous plan
nts (m2)
*tall herbaceouss plant
Using
g the annuaal pollutant removal
r
vallues cited in
n the table, w
we obtain:
GHG
G Sequestra
ation A furrther benefit of green ro
oofs and oth
her green in
nfrastructurre is their ab
bility to
captu
ure and storre – i.e., sequ
uester – carrbon dioxidee. Valuatingg the carbon
n dioxide
sequestration beenefit of greeen infrastru
ucture entaails estimating the margginal social
cost of
o damages that would
d have been caused duee to temperaature increaases if not
for th
he sequestraation carrieed out by thee vegetation
n involved.
xxi
Our formula
f
for estimating the value of sequestereed carbon iss based on tthe findingss
of thee David Suzzuki Foundaation (see Taable S-2). W
We assume th
hat the annual carbon
uptak
ke of these types
t
of veggetation is the same on
n a green roo
of as at grad
de. As the
meth
hodologies reviewed
r
esstimate the sequestratio
s
on value of trees on a large scale
basiss (square killometres orr hectares), and becaus e the valuess are relativvely small,
we use hectares rather than
n meters as units of areea.
Table
e S‐2 ‐ Carbo
on sequestraation values per hectaree for Greateer Golden Ho
orseshoe Greenbelt land tyypes Stored carbon Annual carbon uptake Forest Grassland
d Agriculturral Lands Cropland
Idle land Hedgerow
ws Orchards 919 $2
213 $3332 $317 $3228 $2998 $9
$39.11 $28..46 N
N/A $28.59 $28.559 $28.559 Source: David Suzuki Foundation
n, 2008
We propose
p
the following fo
ormula for calculating
c
the value off annual carrbon
sequestration prrovided by a green roof:
Wherre:
•
b = value of benefit
b
($/yeear)
•
Sd = value of carbon
c
sequ
uestration b
by deciduou
us plants ($//ha•year)
•
ad = area of grreen roof co
overed by d
deciduous pllants (ha)
•
Sg = value of carbon
c
sequ
uestration b
by grasses ($$/ha•year)
•
ag = area of grreen roof co
overed by grasses (ha)
•
Sf = value of carbon
c
sequ
uestration byy productivve agriculturre
($
$/ha•year)
•
af = area of grreen roof co
overed by prroductive crrops (ha)
•
asgg = area of green
g
roof covered
c
by sshort grassees (ha)
•
atgg = area of green
g
roof covered by ttall grasses (ha)
Note:
xxii
4 Case Studies In this section, we apply the methodologies developed in the last section to five case
studies in order to estimate the actual benefits associated with these green roofs
under realistic conditions. The information for these scenarios is drawn from
sources such as Steven Peck's 2008 book AwardWinningGreenRoofDesigns, project
web sites, and interviews with architects and developers.
The case studies were chosen in order to represent a variety of building types and
locations. Together, they provide opportunities for the use of all the calculation
methods presented in the last section.
901 Cherry Avenue, San Bruno, CA The 901 Cherry Avenue building houses offices of the clothing maker GAP Inc. The
building includes a number of sustainable design features, of which the centerpiece
is an undulating 6,400 m2 (69,000 sq ft) semi-extensive green roof. The roof features
a 15 cm (6”) growing medium planted with grasses and wildflowers native to the
San Francisco Bay Area. A notable feature of the 901 Cherry building is that it is
located under the flight path of air traffic landing at the San Francisco International
airport and, as such, is exposed to considerable overhead noise. The green roof
helps provide an acoustic barrier that attenuates sound transmission from aircraft
taking off from and landing at the airport.
benefit sound attenuation stormwater retention air quality GHG sequestration type one time one time annual annual value $303,829 – $783,101
$9,216 – $293,248
$568/year
$18/year
Fairmont Waterfront Hotel, Vancouver, BC The Fairmont Waterfront Hotel is a luxury hotel on the downtown Vancouver
waterfront. When the hotel was built in 1991, a green roof with ivy and pea gravel
paths was initially installed on the large third floor terrace on the building’s south
side; the hotel has a total of 23 storeys. The southern portion of the terrace was
converted to an herb garden in 1994. The garden is maintained year round and
harvested between late march and late fall by the hotel’s restaurant staff. The
produce is used primarily in the hotel restaurant but consumers also include hotel
staff and patrons.
benefit property value (host) type one time value $7,593,888
xiii
property value (neighbour) food production stormwater retention air quality GHG sequestration one time annual one time annual annual $4,409,406
$3,121 ‐ $31,210
$281 ‐ $8,939
$11.54 ‐ $18.73
$0.56 ‐ $0.76
401 Richmond, Toronto, ON Originally constructed in 1899, the building’s 18,580 m2 (200,000 sq ft) floor area
now houses over 140 artists and entrepreneurs. In 1998, a 603.9 m2 (65,000 sq ft)
cedar deck was constructed on a portion of the roof and covered with numerous
planters with flowers, bushes, and vines. In 2005, a further 241.5 m2 (2,600 sq ft) of
the roof were covered with a lightweight extensive green roof system, consisting of
a 2-inch growing medium planted with sedum. The 401 Richmond roof garden has
attracted a considerable amount of attention from the media in Toronto, providing
publicity for the company that owns and manages the building, and indirectly for
the building’s tenants. Residents living in the 14-storey District Lofts building,
directly across Richmond Street enjoy the view onto the 401 Richmond roof garden.
benefit property value (host building) property value (neighbouring condo unit) marketing stormwater retention air quality GHG sequestration type value one time $1,379,756
one time $24,482
one time one time annual annual $83,126
$1,217 ‐ $38,736
$43.79 ‐ $71.01
$2.41 ‐ $3.31
Rooftop Victory Gardens, Chicago, IL The 163.5 m2 (1,760 sq ft) Rooftop Victory Garden is hosted by True Nature Foods,
an organic food cooperative and neighbourhood recycling centre in the Edgewater
district on the north side of Chicago. Urban Habitat Chicago (UHC), a local non-profit
group promoting sustainable practices in urban environments, initiated the project
in 2005. The first harvest occurred in the summer of 2007. The produce grown
during the 2007 and 2008 seasons was mostly distributed among project volunteers
and some was sold at the store below.
benefit property value (host) property value (neighbour) proximity to productive garden type one time
one time value $7,057
$20,660
xiv
property value (neighbour) view onto green roof marketing food production stormwater retention air quality GHG sequestration one time $9,546
one time annual one time annual annual $2,289 – $22,890
$235 – $7,491
$8.47 – $13.73
$0.47 – $0.64
The Louisa, Portland, OR The Louisa is a residential high-rise apartment building with 242 apartments and
ground floor retail, situated in the historic Pearl District of downtown Portland. The
Louisa building is composed of a large podium at the base, which houses the retails
spaces, and a tower set at the back of the podium, which contains the bulk of the
apartments. The green roof is situated on top of the podium and can therefore be
viewed directly from at least half of the apartments in the tower. The green roof
features both extensive and intensive components. The larger (749.8 m2) portion of
the roof is an accessible recreational rooftop garden with intensive vegetation. The
garden is flanked on either side by non-accessible extensive green roofs (292.5 m2
each). These are two storeys higher than the garden as they sit on top of two-storey
townhouse units facing into the garden. Both the intensive and extensive portions
are planted with drought-tolerant native species, which can withstand Portland’s
relatively dry summers with minimal watering.
benefit property value (view) type value one time $2,189,385
$5,641,117
property value (accessible recreational garden) one time stormwater retention air quality GHG sequestration one time annual annual $1,922 ‐ $61,156
$88.89 ‐ $144.15
$3.80 ‐ $5.22
5 Conclusions This report has provided evidence that soft benefits produce economic advantages
for individual property owners, municipalities, and society at large. Despite the fact
that the benefits depend on the local context, we have provided heuristic methods to
estimate the economic value associated with seven soft-benefits. These are methods
that can be used by property owners, developers, architects, municipal officials, and
xv
other stakeholders with information that is often readily-at-hand. The reader should
keep in mind the assumptions that had to be made in order to arrive at these quick
calculation methods. Some of these assumptions, along with the beneficiaries,
benefiting period, and a short statement of the valuation method appear in the Table
S-3.
xvi
Table S‐3 ‐ Summary of Soft Benefit Valuations Benefit Category
Beneficiaries
Assumptions
Property Value
Type Valuation
view onto a green roof property owner* and/or neighbours independent of area one‐time
recreational garden
property owner
independent of area
one‐time
property owner
occupant access, independent of area
one‐time
up to 7% property value
neighbours (adjacent)
public access, independent of area
one‐time
up to 7% property value
neighbours (150 m)
public access, independent of area
one‐time
up to 5% property value
neighbours (300 m)
public access, independent of area
one‐time
up to 2% property value
one‐time
see Table 3
productive garden
up to 4.5% property value (portion above green roof)
up to 11% property value
Marketing
property owner
Food production
property owner
excluding labour and material costs
ongoing
$2‐$20/m2 per growing month
Sound attenuation
property owner
affects top floor only, air traffic noise only, independent of area but assuming extensive coverage
one‐time
1.6% to 4.3% property value of top floor
Stormwater retention
developer, municipality
42.7L/m2 retention capacity
one‐time
$1.44/m2 to 2
$45.82/m
Air quality
municipality, state
ongoing
$521/ha to $839/ha per year
GHG sequestration
municipality, state
ongoing
$28/ha to $39/ha per year
*If the green roof can be seen from at least part of the host property
The case studies presented in this report show that the proposed valuation
methodologies can be applied in real-life situations without requiring large (or
difficult to obtain) data inputs. In general, the valuations returned by applying the
methodologies seem to be of a reasonable magnitude.
Among the one-time benefits proposed here, the property value benefits are by far
the most significant. Properties with accessible green roofs are subject to a 11%
property value premium, while those with rooftop food gardens gain 7% in property
value. Neighbours of both types of green roofs also stand to benefit significantly
from their presence. Those who have views onto a green roof could gain up to 4.5%
of property value, while those adjacent to rooftop food gardens could gain from 2%
to 7%. It should be noted that the sum of the all the property value gains accruing to
xvii
neighbouring properties could be considerably larger than the value of the benefit
accruing to the host property.
Sound attenuation offers one-time benefits on a similar order of magnitude, ranging
from a 1.6% to a 4.3% property value premium on the value of the top floor.
However, this benefit only arises if there is a significant source of overhead noise,
such as air traffic or an elevated train nearby. As for the marketing benefit, also a
one-time benefit, the experience of the 401 Richmond building in Toronto suggests
that it is relatively small – 0.6% of property value in this case.
The value of the stormwater management benefit varies considerably when viewed
as a fraction of property value. In the 401 Richmond case, for example, it is
estimated to be worth between 0.01% and 0.28% of property value, whereas in the
case of the True Nature Foods Victory Garden, it is estimated to be worth 0.2% to
6.9% of the property value. This benefit is not tied to property value but rather to
the area of the green roof; True Nature Foods has low property value but a relatively
large roof and the stormwater benefit is therefore much larger relative to property
value.
Where ongoing benefits are concerned, the food production benefit is much more
valuable than the air quality and GHG sequestering benefits, according to our
methods of estimation. We propose that the value of the food produced on a rooftop
garden is worth $2 to $20 per square metre per month in the growing season. As
most of the North American population lives in places where the growing season is
at least 6 months long, the benefit is therefore worth at the very least $12/m2 of
rooftop growing area per year. In places with a year-round growing season, such as
in the southern coastal states, the benefit could be worth up to $240/m2 per year. In
contrast, the air quality benefit is worth between $0.0521/m2 to $0.0839/m2 per
year and the GHG sequestration benefit is worth $0.0028/m2 to $0.0039/m2 per
year.
The difference between food production and air quality/GHG benefits is well
illustrated by the two case studies that feature rooftop food production. On the
Fairmont Waterfront Hotel herb garden, food production is estimated to be worth
$3,121 to $31,210 per year, while air quality improvement is worth $11.54-$18.73
per year and GHG sequestration is worth a mere $0.56-$0.76 per year. On the True
Nature Foods Rooftop Victory Garden, food production is estimated to be worth
$2,289 to $22,890 per year, while air quality improvement is worth $8.47-$13.73
per year and GHG sequestration is worth a mere $0.47-$0.64 per year.
Given how small the air quality and GHG sequestration benefits are, it is almost
meaningless to include them in an assessment of the benefit values for individual
green roofs. Both of these benefits would be more meaningful if calculated for
numerous green roofs covering a substantial portion of a neighbourhood or city. For
example, as reported above, Bating et al (2005) calculated that if all flat rooftops
across the City of Toronto were extensively greened, the annual cost savings
xviii
attributable to reduction in air pollution would amount to US$1,970,000
(C$2,700,000 in 2008).
Readers are reminded that the methodologies offered here are heuristic in nature;
they are rough estimations based on a number of assumptions that are reasonable
in most cases but may not be applicable in specific contexts. Changes in the
assumptions will of course lead to a different evaluation of benefits. Also, the report
provides calculation methods for a range of greenroof conditions. These are meant
to serve as benchmarks only and of course do not cover all potential situations. The
user is asked to use their own best judgment as to whether and how the
assumptions made and range of conditions covered in this report can be usefully
applied or adapted to their own unique situation.
As already noted, the goal of this report was to allow users to make rough
calculations of benefits without undertaking a major research effort. For the most
part, this has been achieved: the equations require data that is usually readily
available such as property value, building height, roof area, and so on. The sole
exception is the marketing benefit, which requires detailed information on publicity
gained due to the green roof. Our experience with the case studies suggests that
most green roof property owners do not have precise information on media
coverage, if they track it at all. Future research might address this by tacking media
coverage across many green roof projects and generating a more generic formula
for estimating the value of the marketing benefit.
To our knowledge, this is the first attempt in the growing literature on green roofs
to offer a means for calculating the value of a range of soft benefits associated with
the use of the technology. Clearly, however, it is not the last word. Future research
may not only allow us to refine the approaches offered here but to expand the range
of soft benefits covered to include, for example, habitat creation and community
building. If this report has helped put us on this path, then it has served its purpose.
Bibliography Bateman, I., Day, B., Lake, I., & Lovett, A. (2000). TheEffectofRoadTrafficon
ResidentialPropertyValues:ALiteratureReviewandHedonicPricingStudy.
Edinburgh: Scottish Office, Development Department.
Carter, T. & Keeler, A. (2008). Life-cycle cost–benefit analysis of extensive vegetated
roof systems. JournalofEnvironmentalManagement 87, 350-363.
City of Waterloo (2005). GreenRoofFeasibilityStudyandCityWideImplementation
Plan. Public document (http://www.city.waterloo.on.ca/Portals/57ad7180-c5e7-
xix
49f5-b282c6475cdb7ee7/LIBRARY_Plans_documents/GRReport2005Complete.pdf).
Connelly, M. & Hodgson, M. (2008). Sound Transmission Loss of Extensive Green
Roofs - Field Test Results. Acoustics Week in Canada, October 6-8, 2008. Vancouver,
BC: Canadian Acoustical Association.
Crompton, J. (2005). The Impact of Parks on Property Values: Empirical Evidence
from the Past two Decades in the United States. ManagingLeisure 10(4), 203-21.
Cunnigham, N. (2001). RethinkingtheUrbanEpidermis:astudyoftheviabilityof
extensivegreenroofsystemsintheManitobacapitalwithanemphasisonregional
casestudiesandstormwatermanagement. Master’s thesis dissertation, Department
of Landscape Architecture, University of Manitoba, Winnipeg, Manitoba.
David Suzuki Foundation (2008). Ontario’sWealth,Canada’sFuture:Appreciating
theValueoftheGreenbelt’sEco‐Services. Public document
(http://www.davidsuzuki.org/files/Conservation/DSF-Greenbelt-web.pdf).
Kowal, C. (2008). Measuring Urban Green. TheNewPlanner, Winter
(http://www.planning.org/thenewplanner/2008/win/measuringurbangreen.htm)
Peck, S. (2008). AwardWinningGreenRoofDesigns. Toronto: Green Roofs for
Healthy Cities. Voicu, I. & Been, V. (2008). The Effect of Community Gardens on Neighboring
Property Values. RealEstateEconomics36(2), 281-243.
Watcher, S. (2004). TheDeterminantsofNeighborhoodTransformationsin
Philadelphia‐IdentificationandAnalysis:TheNewKensingtonPilotStudy. University
of Pennsylvania, The Wharton School.
Yang, J., Yu, Q., & Gong, P. (2008). Quantifying air pollution removal by green roofs in
Chicago. AtmosphericEnvironment 42, 7266-7273.
xx
1 Introduction The use of green roofs can offer a tangible solution to many challenges faced by
communities across Canada today. Vegetated surfaces offer social and
environmental benefits to building occupants and owners, municipal governments
and surrounding communities, from improved stormwater management, habitat
creation, absorption of air pollutants, and reduced energy requirements, to crime
reduction, community building, and opportunities for food production. In short, the
implementation of green roofs can improve the overall functionality of the
ecosystem, contribute to economic efficiency, and enhance the quality of human life.
Articulating the value of the numerous environmental and social services of green
roofs in monetary terms provides an estimate of their contribution to local and
regional economies and permits governments, land developers and building owners
to assess short- and long-term public and private gains. While some benefits are
directly measurable and have ‘hard’ values (such as the energy savings due the
insulation provided by the soil and vegetation of a green roof), many benefits are
not readily measurable and their values are difficult to estimate (such as the health
benefits of a rooftop garden). For the purpose of this study, those benefits that are
not directly measurable (or calculated based on any line item on the buildings
budget) will be defined as ‘soft’ benefits.
Green roofs and other green infrastructure1 have traditionally been thought of as
cost centres that contribute little or no economic benefit. However, recent work in
the field of environmental economics has brought to light the vital economic
contribution that green infrastructure makes in terms of providing "services" (such
as purifying water and air) to society and individuals alike.2 Excluding soft benefits
from assessments of the value of green roofs could lead to a underestimation of
their real benefit to society and less policy attention devoted to promoting the
infrastructure that gives rise to them. Moreover, without a quantified value, soft
benefits cannot be objectively classified or compared to one another or other
benefits, making rational decisions about the best return on public and private
investment difficult to make. Soft benefit valuation is therefore a critical
undertaking to better inform public policy initiatives and private development
decisions. By considering soft benefits, we obtain a more complete picture of all the
direct and indirect impacts of green roofs on individual buildings, on their
1 Green infrastructure includes wetlands, urban forests and parks, green roofs, community gardens, vegetated
swales, rain gardens and other natural or constructed vegetated areas that perform environmental ecological
services for surrounding human populations.
2 Costanza (1998) has estimated that the world’s ecosystem services provide a benefit in the range of US$16 –
54 trillion (10) per year, with an average of US$33 trillion per year. Global gross national product total is around
US$18 trillion per year.
surroundings, and on society at large.
The purpose of this report is to provide methodologies and case studies that can
offer guidance in attributing economic value to selected soft benefits of green roofs.
Since very few studies to date have focused directly on the economic valuation of
green roof soft benefits, we draw where necessary on studies related to other types
of green infrastructure. It is important to note that our intention here is to offer
methodologies that can be easily employed by stakeholders with limited
information about the property concerned. In other words, our goal is to put
forward heuristic methods that can be used with data that is usually readily at hand.
Needless to say, this approach entails a trade-off between ease of use and the level
of detail and precision. Keeping this in mind, the results obtained with the proposed
methods should be applied prudently.
2
2 Valuation Methodologies The soft benefits of green roofs are not directly tradable and therefore do not have
directly measurable monetary values. To determine their monetary value, nonmarket or indirect valuation techniques must be employed. Estimating the total
economic value of a non-market good or service entails calculating the sum of all
values associated with that good or service. The two main categories of value are
use and non-use values. Use values can either be direct or indirect. Direct use value
refers to the value that is derived from actual or planned use of a particular
environmental service or good. Recreation and food production are two examples of
direct use values. Indirect use value occurs when people benefit from an
environmental amenity without consciously using it. Water filtration, climate
regulation are examples of the indirect use values of environmental amenities. Nonuse value refers to the value that individuals place on an environmental amenity
without having any planned use for it. An example of a non-use value is the intrinsic
value that people attribute to an environmental amenity (like the boreal forest)
simply for its existence. The methods used to estimate non-use values are
considerably more complex and are beyond the scope of this report.
Non-market valuation techniques have been developed in order to estimate the net
value that the public or individuals attribute to environmental amenities such as
green infrastructure. Three general categories of nonmarket valuation
methodologies exist. The first category,revealed preference methods (i.e., travel
cost, hedonic pricing, market comparables, and cost avoidance) uses behaviours and
information observed in markets to estimate non-market values. The second
category, stated preference methods, which includes the contingent valuation
technique, attributes economic value by asking people their willingness to pay for a
service or willingness to accept compensation to voluntarily forgo a service. The
third category is avoided cost analysis, which can be used to determine the value of
green infrastructure by quantifying the costs that would be incurred if the services
provided by the infrastructure were not available or had to be provided by building
conventional infrastructure.
Table 1 presents a summary of non-market valuation methods explored in this
report and the strengths and limitations of each. The methodologies and specific
valuation frameworks applicable to green infrastructure benefit valuation are
outlined in greater detail below.
3
Table 1 ‐ Non‐market valuation techniques Methodology Hedonic pricing Market comparables Contingent Valuation Avoided Cost Analysis Description Assumes that the environmental characteristics (e.g., a pleasant view or the disamenity of a nearby landfill site), as well as other property features, are reflected in property prices. The value of the environmental component can therefore be captured by modeling the impact of all possible influencing factors on the price of the property. Hedonic pricing can measure direct and indirect use value. Uses data on the price of similar goods or services that are traded in the market as a proxy for willingness‐to‐pay. Typically administered through a public survey. Consumer or clients are asked how much they would be willing to pay for a good or service, or how much they would be willing to accept in compensation for its loss. Uses cost of replacing ecosystem services with conventional infrastructure, or avoided health costs to estimate value of ecosystem services. Value captured Strengths Limitations Direct and Indirect use Based on market data and prices – relatively important figures. Very data‐intensive approach to economic valuation (e.g.: identifying all relevant attributes for a particular good). Choosing the appropriate variables is difficult. Direct and indirect use Market data readily available and robust Limited to benefits for which markets exist. Use and non‐
use Captures use and non‐use ecosystem functions Based on individual responses, people tend to under‐value amenities. Direct and indirect use Costs can often be estimated from market prices Avoided costs do not necessarily reflect the social value of an ecosystem service. Source: Adapted from DEFRA, 2007 p.37
2.1 Revealed Preference Methodologies Revealed preference methodologies are relevant for estimating the monetary
benefit accrued to occupants and/or owners of a building as a result of the addition
of a green roof. These methodologies rely on observed market behaviours - i.e., how
much people actually pay for existing goods and services available on the market.
Prices of non-market goods are inferred by associating them with consumers’
purchase decisions using a defined theoretical framework. Below, three revealed
preference methods are described: hedonic pricing, travel cost, and market
comparables.
2.1.1 Hedonic Pricing Hedonic pricing is a methodology that has been extensively used to estimate the
economic value ascribed to various non-market environmental goods and services
4
such as air and water quality, aesthetic views and proximity to green spaces or
recreational sites. It is most commonly used to evaluate the individual contribution
of environmental amenities on real estate prices. The technique regards a good as a
set of attributes and considers the total economic value of that good as the sum of
values of each attribute. First, a good or service must be decomposed into its
constituent attributes. Regression analysis is then used to estimate the individual
contribution of each attribute to the total value of the good. The hedonic pricing
model is usually expressed using the following function (Hidano, 2002):
valueofagood =
(valueofattribute1) (quantityofattribute1) +
(valueofattribute2) (quantityofattribute2) +
…+
(valueofattributen) (quantityofattributen)
Variations in real estate value are dependent on a large number of factors. Hedonic
pricing models have estimated the variations based in the following attributes: the
square footage of a property, the age of the property, number of bedrooms, number
of bathrooms, number of units, number of storeys, distance from the central
business district (CBD), transportation access and the neighbourhood’s socioeconomic characteristics.
Hedonic pricing may be used to estimate direct and indirect use values. One
shortcoming of the hedonic pricing approach is that it’s a very data intensive
methodology. Identifying every relevant attribute that makes up the total value of a
good can be a long and difficult process.
2.1.2 Market Comparables The market comparables method examines the amount that is charged and paid for
by consumers of a good or service traded in the market that is comparable to the
one being assessed. When a good or service is provided in the private sector,
charges collected by firms offer good proxies for people’s willingness to pay for a
similar good or service that is offered for free or below market price through the
public sector. Private sector market comparables provide good estimates of the
value of a non-market good given that they are based on the actual cost of provision
and consumer preferences and demand for this good. When no similar good or
service is provided by the private sector, values can be derived from charges
collected by public sector providers such as municipal, provincial or federal levels of
governments (e.g., park entrance fees). In most cases, these institutions will charge
well below market rates or actual willingness to pay for a good or service. For this
reason, the prices charged by public sector providers are usually well below
people’s willingness to pay and should be considered as the absolute minimum
value of a good or service.
2.2 Stated Preference Methodologies Stated preference methodologies attribute monetary value to environmental goods
5
and services based on people’s stated preferences rather than their observed
behaviour. Surveys are used to collect information about how much an individual is
willing to pay for a particular environmental good or service. The technique can also
be used for assessing order of preference for a set of goods.
A number of problems have been associated with stated preferences methods. One
critique is that people are potentially unwilling or unable to express willingness to
pay truthfully or accurately - i.e., there can be a discrepancy between how much
people state they are willing to pay and how much they actually pay for a given good
or service, resulting in inaccurate estimates of that good’s or service’s monetary
value. Nevertheless, this valuation method is useful in estimating the value of goods
and services that are not sold on the market. This can include goods and services
that are provided by the public sector for free or below cost. It can also include
goods and services that are not widely available and for which revealed preferences
therefore cannot be observed (Champ et al., 2003).
The most common stated preference methodology is contingent valuation. Surveys
are used to ask people how much they are willing to pay for a particular
environmental service or good. Alternately, the public can be asked how much they
would be willing to accept in compensation for the loss of an environmental
amenity. Contingent valuation is the economic valuation technique most commonly
employed when revealed preferences techniques are not applicable.
Contingent valuation could be applied, for example, to a project to enhance a
freshwater wetland, which would improve sport fishing opportunities. The direct
beneficiaries are people who fish recreationally. Valuation would be used to
estimate the maximum that anglers would pay for this improvement in fishing. Each
angler’s expression of his or her maximum willingness to pay represents how much
the angler is prepared to compensate the rest of society for the increased individual
enjoyment gained from the improved recreational fishing. Maximum willingness to
pay is aggregated for all anglers who benefit to determine whether the benefits of
the wetland project exceed the costs, which facilitates an assessment of whether
public funds should be spent on the project.
2.3 Avoided Cost Methodologies In circumstances where an ecological service is difficult to value by any of the above
methods, analysts advocate using avoided cost methodologies. This approach can be
used to determine the value of green roofs and other green infrastructure by
quantifying the costs that would be incurred if the services were to be provided with
conventional infrastructure. For example, the presence of a wetland may reduce the
cost of municipal water treatment for drinking water because the wetland system
filters and removes pollutants. We can therefore use the cost of an alternative
treatment method, such as the building and operation of an industrial water
treatment plant, to represent the value of the wetland’s natural water treatment
service (De Groot, 1992).
6
It is important to note that this method does not provide a direct estimate of the
value of the ecological service to the public, but only the cost of replacing that
service if it were lost. It is a valid approach if the human-made alternatives are
equivalent in quantity and magnitude to the natural functions; the alternative is the
least-cost alternative method of performing the function; and individuals in
aggregate would be willing to incur these costs to obtain the services (DEFRA,
2007).
7
3 Valuation of Benefits This section presents methodologies for valuating a variety of soft benefits that
accrue to green roofs. While our primary focus is on green roofs, we include
information related to other forms of green infrastructure if the information is
readily transferrable to green roofs. The purpose here is to provide readers with
non-technical methods for estimating the soft benefits associated with a green roof
project based on readily available information and without the need for undertaking
major research.
The benefits that are included here are those for which we could find relatively
straightforward valuation methods that could be applied by non-specialists with
limited resources for data gathering. The proposed methods were gathered from
current practices and the existing literature. The benefits covered are:
•
•
•
•
•
•
•
property value increases
marketing
sound attenuation
food production
stormwater retention
air quality
GHG sequestration
For each benefit, we discuss the nature of the benefit, review existing practices and
literature that contributes to an understanding of the monetary value of the benefit,
and offer a method that could be used by non-specialists to estimate the value of
that benefit in a given context.
It is important to note that the methodologies offered here are heuristic in nature;
they are rough estimations based on a number of assumptions that are reasonable
in most cases but may not be applicable in specific contexts. The assumptions are
clearly stated in the description of each methodology below. The user is asked to use
their own best judgment as to whether the methods provided can be usefully
applied or adapted to their own unique situation (e.g., length of growing season,
depth of growing medium, or mix of plant types). For most of the benefits included
in this report, values for a reasonable range of situations is provided for readers to
consider when evaluating the benefits of a specific green roof. The ranges provided
are benchmarks only and of course do not cover all potential situations.
Although all soft benefits tend to be context-specific to some degree, some benefits
are simply too context-specific to include in an analysis of this type and are excluded
from the following analysis. Examples of excluded soft benefits are improved
8
aesthetics, crime reduction, increased biodiversity, and building a sense of
community.
The different benefits covered in this section accrue to different stakeholders; some
go to the owner(s) of the building on which the green roof is found (e.g., property
value increases), others go to the municipality (e.g., stormwater retention), while
some go to the regional (e.g., air quality improvements) or planetary (e.g.,
greenhouse gas mitigation) population. Benefits accrue either on a one-time basis
(such as an increase in property value) or an annual basis (such as greenhouse gas
mitigation).
It is important to note that the methods presented below are intended to calculate
the gross value of the benefits considered. The methods do not account for the costs
involved in producing the benefits. In particular, we do not account for the extra
costs involved in creating a green roof compared to a conventional roof. In the case
of benefits that consist of an increase in property value, we do not consider the
higher property taxes that could be applied as a result. In the case of food
production, we do not account for direct inputs such as the cost of materials and
labour.
All monetary values given below are in US dollars unless stated otherwise. Where
possible and relevant, we have adjusted the values for inflation to show the value in
2008 dollars.
3.1 Property value increase Green infrastructure investments have been shown to positively affect the property
value of nearby real estate. In the case of green roofs, this benefit would accrue to
the owner or owners of a building with a green roof and, to a lesser degree, to
owners of surrounding properties. As property taxes are in most cases proportional
to property value, a benefit in the form of increased property tax revenues can
accrue to municipalities. Miller (2001), Morancho (2003), Voicu & Been (2008),
Edwards (2007) and Wachter (2004) have all used the hedonic pricing methodology
to measure the relationship between the selling price of a residence and its distance
from an urban greenspace, park, community garden or wetland. Although it is a very
data intensive methodology, the hedonic pricing model is the most common method
used to measure the impact on property values from nearby green infrastructure.
Essentially, the hedonic pricing model estimates the impact of green infrastructure
on real estate market value by comparing properties that differ with respect to their
distance from an amenity such as a park, wetland, open space or community garden.
The positive relationship between the relative value of a dwelling and its distance
from green infrastructure elements is called the proximity principle (Edwards,
2007). The proximity principal suggests that the value of parks and other green
infrastructure is captured in the price of surrounding real estate. The value of the
amenity is capitalized in the form of home prices and property taxes collected by
9
local governments. Here, we present a few case studies that have estimated the
relative impact of green infrastructure investments on property prices using the
hedonic pricing model.
•
Using data on over 3000 property sales between 1980 and 2003 in the
New Kensington area of Philadelphia, Wachter (2004) quantified the
effect that investing in green infrastructure would have on property
values. Specifically, the author looked at the impact of converting
vacant lots into green spaces on surrounding home prices. A hedonic
regression model was developed that integrated variables on sales
and structural characteristics of homes (e.g., date of sale, number of
storeys, home size, lot size, elements of location). The model included
data on the real estate’s proximity to green infrastructure as well as
its distance from disamenities such as vacant lots. Study results
suggested that replacing unsightly vacant lots with grass landscapes
and trees increased surrounding property values by up to 30 percent.
Houses sold within 50 feet from new tree plantings showed a 9
percent increase in property value. In the sample neighbourhood
chosen for this study, property value increased by $12 million due to
vacant lot conversion and $4 million due to tree plantings. Based on
an effective tax rate of 2.64% accumulated over 20 years, the benefits
gained from lot improvements and new tree plantings would
represent a respective property tax base increase of $6,336,000 and
$2,112,000 for the local government (Steve Wise, personal
communication).
•
Also in Philadelphia, the Trust for Public Land (2008 a) used a
hedonic pricing model to estimate the effect of proximity to a park on
property value. They calculated the total assessed 2007 value of all
properties within 500 feet of a park to $4,387,574,062 (or
$13,776,982,555 when corrected for under assessment, calculated to
314% around “average parks”). Assuming conservatively that parks
contribute on average 5% to the assessed value of properties, it was
calculated that the portion of total assessed property value attributed
to proximity to parks was $219,378,703 (or $688,849,128 corrected
for under assessment). In terms of tax revenues, proximity to parks
was calculated to yield additional annual property tax revenues of
$82.64 per $1,000 of assessed property value.
•
Edwards (2007) conducted a similar study in the San Francisco region
by dividing homes into two categories; residences that were 500 feet
or less of a park and homes located between 500 and 1000 feet of a
park. Results from a hedonic pricing model showed that, all else being
equal, homes in the former category sold for an average of $125,838
more than residences in the latter category. The author underlines
that this is an underestimation of the true premium of urban parks in
10
San Francisco because there is a wide range of other possible
economic benefits associated with urban parks such as health
benefits, environmental benefits, and revenue generated from special
events.
•
An analysis of about 30 studies exploring the relationship between
real estate value and proximity to parks confirmed the argument that
parks and open spaces contribute to higher proximate property
values (Crompton, 2005). The reviewed studies show that variations
in size, usage and design of parkland and differences in residential
zones that surround them influence the magnitude of the park
proximity premium. In particular, certain studies, such as Miller
(2001), have observed that lot size has a significant impact on
magnitude of the premium. In general, properties with small lots that
presumably have limited private open space appreciate parks more
than properties on large lots with generous open space. Such
variations notwithstanding, Crompton proposes a 20 percent increase
in the value of properties abutting or fronting a park area as a point of
departure that decision-makers may use to calculate property value
increases attributed to urban green spaces.
•
Voicu and Been (2008), using a hedonic price model, found that the
implementation of new community gardens had a significant impact
on surrounding property values in New York City. They studied the
effect of property values at four different points in time with respect
to the completion of the community garden: at the moment of
completion, one year, three years, and five years after completion. In
all cases, the effect was calculated for three ranges of distance from
the community garden: abutting the garden, up to 500 feet from the
garden, and up to 1,000 feet from the garden (see results in Table 2
below). The authors observed that value of properties near
community gardens, especially those abutting them, increased over
time after implementation. The authors also found that the effect was
significantly stronger in low-income areas than in high-income areas.
Table 2 ‐ Impacts of a typical community garden on residential property values Time since completion Right after completion 1 year 3 years 5 years Distance to garden site (meters) 0 150 %* $** % 3.4 3,207 2.5 4.1 3,607 2.8 5.6 4,971 3.6 7.4 6,551 4.7 $ 2,191 2,450 3,172 4,111 300 % 1.5 1.5 1.6 1.9 $ 1,355 1,293 1,373 1,670 *percent change in price within ring versus outside the ring
**change in price applying the percent change in price to the median per unit sale price of properties
sold within the ring
11
Source: Voicu and Been, 2008
The hedonic pricing model would be an ideal technique to calculate green roofs’
effect on property value. Using this method, the value of buildings with green roofs
could be compared to that of buildings with conventional roofs while controlling for
other variables that are known to have an effect on property value. In the hedonic
price model, green roofs could be represented as a single Boolean value, denoting
whether the building has a green roof or not. This would be the least data intensive
approach but would also provide the least accurate estimate, failing to account for
qualitative differences between green roofs. A more accurate approach would be to
use a continuous variable, denoting the percentage of the given roof that is green.
Additional Boolean variables could be added to represent qualitative differences
between green roofs (e.g., extensive versus intensive, accessible versus inaccessible,
etc.).
At present, however, there are no hedonic studies that have measured the potential
of green roofs in increasing the selling price of a condominium or other residential
building. In the absence of hedonic pricing studies looking specifically at the effect of
green roofs on property values, we must make an estimate using studies performed
on other types of green infrastructure. The selection of the appropriate type of
green infrastructure for this purpose would depend on the features of the green roof
being assessed, i.e., whether the roof is accessible, whether food is grown on it, and
whether it is visible from other locations.
An accessible green roof could be used in two broad ways: as a recreational space or
as a food production space. In the former case, it would seem that the best
comparable would be at-grade public parks; in the latter case, the best comparable
would be at-grade community gardens. The key difference between rooftop green
infrastructure and at-grade green infrastructure is that the former are likely to be
accessible only to the occupants or users of the building with the rooftop facility
whereas the latter are likely to be accessible to the community at large. Thus, the
benefits of rooftop infrastructure accrue mostly, if not exclusively, to the properties
on which it is located; the benefits, if any, accruing to neighbouring properties are
likely to be limited.
In the case of a green roof that is visible from surrounding buildings, however,
benefits may accrue to neighbouring properties. In this case, an appropriate
comparable would be the value of having a view onto an at-grade park or woodlot.
Accessibility to the rooftop would not be a significant consideration in this case.
3.1.1 View onto a Green Roof Assuming that having a view onto a green roof has a similar effect to new tree
plantings, the value of the benefit accrued to owners of properties is 9% of the value
of the portion of a building that affords a direct view onto a green roof. This is
based on Wachter’s (2004) finding that tree planting along a street in front of a
property increases the property's value bys up to 9%. Where neighbours of the
12
green rooftop are concerned, we assume that greening a rooftop is equivalent to
tree planting at-grade . For them, the greening of the rooftop has much the same
effect as tree planting – it adds greenery but does not change the amount of
recreational green space to which they have access. We do not attribute any
increased value to a green roof without trees.
Whole building gain in property value For the purpose of estimating the value of the benefit for a whole building, we
assume that only half the neighbouring storeys above the green roof are oriented so
as to afford a view onto it. The increase in property value that accrues to a building
with a view onto a green roof can therefore be estimated using the following
formula:
1 h −h
b = 0.09⋅ ⋅ v
⋅ vv
2 hv
= 0.045⋅
hv − h
⋅ vv
hv
Where:
•
b = value of benefit ($)
•
vv= value of neighbouring property with a view onto the green roof
($)
•
h = height of the green roof host building (storeys)
•
hv = height of the building with a view onto the green roof (storeys)
Single unit gain in property value For the purpose of estimating the value of the benefit for a single unit in a building
that has a direct view onto a green roof, we propose using the following formula:
b = 0.09⋅ v v
3.1.2 Recreational Rooftop Garden A rooftop garden that is accessible to building dwellers will offer recreational
benefits that may be reflected in the value placed on the building. To estimate this
value, we turn to studies that have assessed the impact on housing values in
locations abutting public parks. Using the hedonic method, Crompton (2005) has
suggested that homes adjacent to public parks have about a 20% higher property
values than similar homes distant from parks.. Given that an abutting park offers
13
both recreational and view benefits, we deduct the view benefit (9% of property
value) calculated above to arrive at a recreational benefit of 11%.
We propose the increase in property value yielded by a recreational rooftop garden
be estimated using the following formula:
b = 0.11⋅ v
Where:
•
b = value of the benefit ($)
•
v = value of the green roof host property ($)
3.1.3 Productive Rooftop Garden Assuming that having a productive rooftop garden is tantamount to abutting an atgrade community garden, we propose that the value of the long-term benefit
accrued to the owner of the property be estimated at 7% of the value of the
property. This is based on Voicu and Been’s (2008) finding that, on average,
properties abutting typical community gardens increased in value by 7.4% by five
years after the construction of the garden. As we do not know from these findings
what the effect is in the longer term, we assume the value remains constant at the
five-year level.
We propose the increase in property value yielded by a private, productive rooftop
garden be estimated using the following formula:
b =0.07⋅v
Where:
•
b = value of benefit ($)
•
v = value of green roof host property ($)
If the productive rooftop garden is open to non-occupants of the building then it is
more likely that benefits will accrue to owners of neighbouring properties. In this
case, we assume that the rooftop garden behaves exactly like an at-grade
community garden. In the long-term, the value of the benefit accrued to
neighbouring property owners is 7% for owners in the building with the rooftop
community garden and the immediate vicinity of the host building, 5% for those up
to 500 feet away, and 2% for those up to 1,000 feet away. Again, the values are
based on Voicu and Been (2008) and assumed to hold at their five-year level.
We propose the increase in property value accrued to a neighbouring property of a
publicly accessible productive rooftop garden be estimated using the following
formula:
14
b = F ⋅v
Where:
•
b = value of benefit ($)
•
v = property value ($)
•
d = distance from green roof host property (meters)
•
F= distance factor (function of d)
•
F = 0.07 when 0 ≤ d ≤ 5 m
•
F = 0.05 when 5 m < d ≤ 150 m
•
F = 0.02 when 150 m < d ≤ 300 m
•
F= 0 when d > 300 m
Let:
3.1.4 Area‐Wide Benefit The above stated formulas are intended for calculating the value of proximity
benefits that accrue to individual properties. Municipal decision makers may be
more interested in the total, area-wide increase in property values resulting from a
green roof project. In this case, it is necessary to sum the values of the benefit
accruing to the host property with those accruing to neighbouring properties.
b = b
total ∑ n
Where:
•
btotal = total area-wide property value benefit ($)
•
bn = property value benefit of an individual property ($)
The property value benefit for each individual property (bn) must be calculated
using the appropriate formula for the given case – i.e., recreational or productive
rooftop garden, nearby property, or property with a view. In cases where more than
one formula applies, both values should be calculated but only the larger of the two
should be used in the summation.3 For example, if a building affords views onto a
directly adjacent productive rooftop garden, both the productive rooftop garden
It is unknown whether these two benefits are additive. In such cases, it is common practice to use the larger of
the two benefits.
3
15
formula (3.1.3) and the view onto a green roof formula (Error!Referencesource
notfound.) apply. The benefit attributed to proximity to a productive garden will
clearly be larger than that attributed to having a view onto it and should therefore
be used in the area wide benefit summation.
3.2 Marketing Green infrastructure in general and green roofs in particular not only increase the
monetary value of a property due to proximity benefits, but may also improve the
marketability of real estate. The mass media and the public’s interest in
environmentally friendly products and services is increasing rapidly in Canada.
Green roofs and other green infrastructure on or near a building can therefore be
considered as a marketing amenity that increases a development’s exposure and
enhances the absorption rate of its units.
Applying the comparable costs methodology, one way of estimating the marketing
benefits of green infrastructure would be to assess the value of the publicity gained
as a direct consequence of green infrastructure investments. The two Canadian case
studies below illustrate green infrastructure and green roofs’ marketing potential.
•
Dockside Green, a 15-acre mixed–use community under development
in Victoria, British Columbia. The development has focused on
maximizing green space and green infrastructure amenities by taking
steps such as locating 95 percent of all parking spaces underground,
reducing the buildings’ foot print, installing green roofs on residential
and commercial buildings, planting over 1,000 trees on the site,
converting an adjacent piece of municipal land into a park and
reducing or eliminating the need for streets on the property. Garden
plots have been installed on the roofs of residential buildings and the
connectivity of at-grade green space has ensured its accessibility to
Dockside Green residents as well as citizens living outside the
community. Dockside green is also integrating green wall elements in
the development (City of Victoria, 2005). The project has garnered
extensive amounts of media coverage for its green amenities. Since
2005, Dockside Green has benefited from media coverage worth
about $5 million. A developer representative reports that they have
had greater sales compared to other real estate presentation centers
in the area. The first phase of the development is already occupied
and 80 percent of units have been sold for the second phase, which is
due to open in February 2009 (Martine Desbois, personal
communication).
•
Urbanspace is a property group that owns and operates two heritage
buildings in downtown Toronto, which have been retrofitted with
green roofs. Robertson Building tenants have access to a 4,000 square
feet rooftop garden, which covers approximately half of at the total
16
roof area. The 401 Richmond building has a 2,600 square feet
extensive green roof and a 6,500 square feet deck that includes a
container garden. This rooftop garden is accessible to both building
tenants and the public at large. The roofs were created with the
intention of providing common space where people can socialize and
relax while improving the general livability of the buildings.
Both of the buildings’ green roofs have garnered public attention
through media exposure. The building owners have used the media
attention the gardens have attracted as a way to market the buildings
as a whole. Although Urbanspace has never invested in advertizing
campaigns, vacancies in both buildings are rare to non-existent and
waiting lists are extensive. Many of the properties’ prospective
tenants have heard of the buildings because of the public attention
they have gained due to their respective green roofs. Tenants have
also expressed that the accessible green roofs are amenities that they
value and improves the livability of the buildings.
The marketing benefits of green roofs will depend on a number of factors that are
unknown in advance or difficult to quantify, such as the current interest of local
media in green infrastructure and green buildings. Nonetheless, as the case studies
suggest, the marketing benefits can be estimated based on the value of the publicity
received due to the presence of the green roof in the project. The value of the free
publicity received can be estimated by comparison to the cost of advertizing in three
media: radio, television, and print. The cost for each of the three media is broken
down into the production cost plus the cost of running the ad. The former can be
assumed to be constant as it is a onetime cost. The latter is the cost of having the ad
aired on radio and television and printed in newspapers.
The value of free publicity can in principle be estimated according to the following
formula:
b =(pradio + rradio ⋅tradio)+(ptv + rtv ⋅ttv )+(ppaper + rpaper ⋅ l)
Where:
•
b = value of the benefit ($)
•
pradio = radio ad production cost ($)
•
rradio = radio ad running cost (airtime) ($/30s spot)
•
tradio = total radio equivalent airtime (30s spots)*
•
ptv = tv ad production cost ($)
•
rtv = tv ad running cost (airtime) ($/30s spot)*
17
•
ttv= total tv equivalent airtime (30s spots)
•
ppaper = newspaper ad production cost ($)
•
rpaper = newspaper ad running cost (printing) ($/column inch)
•
l = total equivalent column length (column inches)
* Total airtime is divided by 30 to convert to number of spots.
Radio and television ad airtime is generally sold in 30-second blocks or ‘spots’.
Unlike newspaper ad prices, radio and television ad prices are not published; rather,
they are negotiated on an individual basis with every advertiser.4 For both media, ad
prices are related to the size of the audience. For a radio station, the size of the
audience will depend mostly on the time of day, the size of the market (i.e., the
population within the radio broadcast’s reach), and the station’s relative popularity.
Single radio spots (i.e., not sold as part of a bundle of several spots) generally range
from $50 to $1,000. For television, the size of the audience depends more on the
popularity of individual programs than on the popularity of any given station; the
programs with the highest ratings command the highest advertizing prices. Spots
that run on national networks during weekday prime time range between $80,000
and $600,000 and average around $120,000 per 30-seconds. However, spots on
local stations during local programming, such as a local news report, are
considerably less expensive. Market research shows that, in the US, the cost of
television advertizing is on average US$20 (C$24) per 1,000 viewers (Grover, 2006)
but the cost of airing an ad on a local stations in medium markets outside prime
time can be as low as US$5 (C$6) per 1,000 viewers or even lower (Gaebler,
undated). Thus, a show with 100,000 viewers will command a price in the range of
$500 to $2,000 for airing a single 30 second spot.
Newspaper space is priced by ‘modular agate lines’ (MALs) in Canada or by column
inches in the US (there are 14 MALs per column inch). Generally, the cost of running
an ad is proportional to the circulation of the newspaper – a local paper in a small
market will have low prices while a leading paper in a large city or a nationally
distributed paper will have higher prices. Some national papers (e.g., The Globe and
Mail in Canada) run a few local or regional editions with different ads, which are
usually priced lower than ads printed nationwide. As real estate ads are generally
intended for the local audience, the advertizing prices of local papers or local
editions of national papers are more relevant for estimating the value of free
publicity.
In performing an estimate of the value of free publicity, it would be very difficult to
account for all the variations in advertizing cost between different media outlets and
4 We contacted a few television stations, all of which refused to send us their advertizing rate cards stating that
they would only send to professional media buyers.
18
different times of day, in the case of radio and television. Ultimately, the key
determinant of the cost of radio and television airtime and column inch price in a
major newspaper is the size of the market, which is proportional to the population
of the area covered by the given radio or television station or the distribution area
of a newspaper. For the purpose of estimating free publicity, we propose using the
population of the census metropolitan area (CMA) in Canada and of the
metropolitan statistical area (MSA) in the US as proxies for market size. We propose
that the size of the audience for any of the three media be assumed to be 5% of the
metropolitan population.
A sample of average advertising costs for the three media are summarized in Table 3
below. Where data was unavailable, costs are estimated. For the cost of television
ads, a cost of US$10 per 1,000 viewers was assumed.
Table 3 ‐ Average cost of radio, television, and newspaper advertizing in selected cities Radio (30s spot) City Toronto, ON Television (30s spot) Newspaper (column inch) Metro Cost per Cost per Cost per Population Average Average Average 1,000 1,000 1,000 cost cost cost listeners viewers readers 5,555,912 $250 $0.90 $2,778 $10 $392 $1.41 Vancouver, BC 2,285,900 $158 $1.38 $1,143 $10 $199 $1.74 Minneapolis, MN 3,175,041 $173 $1.09 $1,588 $10 $303 $1.91 19,750,000 $1,405 $1.42 $9,875 $10 $1,575 $1.59 New York, NY San Francisco, CA 7,264,887 $899 $2.47 $3,632 $10 $613 $1.69 Seattle, WA 4,038,741 $209 $1.03 $2,019 $10 $365 $1.81 $516 $1.38 $3,506 $10 $597 $1.69 Average Sources: www.gaebler.com, www.theglobeandmail.com, www.conestoga.ca, www.canada.com, and
Lotz, personal communication.
All prices in US dollars.
Figures in italics are estimates.
To convert mentions on radio or television to equivalent paid airtimes, we propose
the following conservative rules and applying the discount factors described below.
1. A brief mention of a green roof project in a factual news report is equivalent
to one 30-second spot
2. A factual news report on the subject of the green roof project is equivalent
minute-to-minute to a television spot; the duration of the news report should
be rounded down to the nearest 30 second increment (e.g., a 2:09 news
report is rounded down to 2:00 and therefore equivalent to four 30 second
spots).
19
3. A positive endorsement in an editorial or opinion piece is equivalent to
twenty 30 second spots (Lotz, personal communication)
Discount factor (D):
•
If mention is on a major network, D= 1 (no discount)
•
If mention is on a specialty channel, D = 0.1 (90% discount)
•
If mention is on a public access channel, D = 0.05 (95% discount)
To convert mentions in the newspapers to column inches, we propose applying the
following general rules and applying the discount factors described below:
1. In a factual article whose main subject is not the green roof project, each
sentence in which the project is mentioned is worth one column inch.
2. A factual article whose main subject is the green roof project is worth double
the number of column inches taken by the article
3. A positive endorsement in an editorial or opinion piece whose main subject
is not the green roof project is equivalent to a half-page ad or 64 column
inches.
4. A positive endorsement in an editorial or opinion piece whose main subject
is the green roof project is equivalent to a half-page ad or 128 column inches.
5. If mention includes a picture, convert picture to column inches by dividing
the area by 2 (one column is 1.96” wide).
Discount factor (D):
•
If mention is in a major daily newspaper, D= 1 (no discount)
•
If mention is in a citywide weekly magazine, D = 0.25 (75% discount)
•
If mention is in a specialty or community publication, D = 0.1 (90%
discount)
3.3 Food production and food security Urban agriculture (whether at grade or on rooftops) can provide city-dwellers with
a source of fresh produce, improved diet and important household budgetary
savings. Successes in cities across North America illustrate the potential relief that
urban food production can offer to those in need. Combining average garden plot
yields and cost savings from the purchase of produce (based on market prices) can
help us evaluate the monetary value of urban food production. Furthermore,
20
calculating the amount of locally grown produce that can be distributed to lowincome citizens through community organizations such as food banks can provide
an estimate of the food security benefits related to urban agriculture. Urban food
production has many other potential benefits, such as CO2 absorption, social
cohesion and health effects. With the exception of CO2 absorption, which is
addressed in Section 3.6 below, these topics are not explored here due to a lack of
existing research.
To help assess the productivity and monetary value of urban agriculture, we have
compiled some case studies from Canada and the US:
•
A study of the urban agriculture potential of an infill development in
Vancouver, British Columbia, estimated that a market garden could
yield 50,000 kg/ha of food. Market gardens generally grow a variety
of produce, usually focusing on highly perishable items that fetch a
high price. The authors calculated that gardening one hectare of land
would fulfill 3% of the 10,900 to 13,800 community residents’
vegetable needs (Barrs, 2002). Given that Canadian households with
middling incomes ($40-59K) spend around $20 per week on fruits
and vegetables (Statistics Canada, 2002), we can estimate that 3% of
annual household spending on the same would be $31.20. Given the
average household size of 2.25 people (City of Vancouver, 2006), a
community of 10,900 to 13,800 residents would have 4,844 to 6,133
households. Therefore, we can estimate that a market such as the one
described in this scenario could save the community between
$151,100 and $191,300.
•
The rooftop herb garden at the Fairmont Waterfront Hotel in
Vancouver has provided important monetary benefits for the hotel’s
restaurant. Herbs grown on the 195.1 m2 (2,100 sq. ft.) rooftop garden
provide an estimated $25,000 to $30,000 annual saving in food costs
for the hotel restaurant (September & Peck).
•
Commercial urban agriculture enterprises across North America offer
important sources of income to urban and peri-urban food producers.
The Kon Kai urban farm in Berkley California earns on average
$250,000 to $300,000 per year from the gourmet lettuces it grows on
1618.76 m2 (17417.9 sq. ft.) of land (Barrs, 2002).
•
In 1991, a study revealed that, on the average 65 m2 (720 sq. ft.)
community garden in Newark, New Jersey, annual vegetable
production amounted to just over $500 (Patel, 1991). The net
economic benefit of gardens was estimated to be $475 after deducting
a $25 average input cost, not including labour. When adjusting for
inflation this amounts to an economic benefit of over C$800 in 2008.
21
•
Action Communiterre is non-profit organization that operates 10
collectively managed organic gardens in the Notre-Dame-de-Grâce
area of Montreal. Vegetables harvested from the garden are shared
among the volunteer gardeners and the rest is donated to community
organizations such as local food banks and housing projects. Garden
volunteers are also offered informational workshops on gardening,
composting, recycling, and food security. In 2007, 1,547 kilos of
vegetables were harvested from the 4,900m2 land area occupied by
the organization’s 10 collective gardens. The organization has set a
goal of harvesting 2,500 kilos in the gardens during the 2008 growing
season. In 2007, the group initiated a rooftop vegetable garden pilot
project, which produced 150 kilos of fresh vegetables. For the 2008
growing season, the group aims to cultivate around 750 kilos of
vegetables on the 80 m2 of cultivable rooftop land area.
•
In Seattle, the P-Patch program provides gardening space to over
6,000 gardeners on 23 acres of land across the city and provides a
source of fresh produce and economic opportunities to low income
citizens. A 2007 survey of community gardeners in Seattle revealed
that between the months of April and October, 36 percent of
respondents received over half of their produce needs from their
garden plot (Rich McDonald, personal communication). Seattle
gardeners also contribute to local food security by donating
approximately 44,000 pounds of fresh produce to local food banks in
2007. Out of this, about 11,000 pounds of fruit (mostly plums) were
harvested from Seattle fruit trees and delivered to people with limited
access to organic produce. At a retail price of $2.99 per pound, the
organic plum harvested through the project represented a direct
benefit of over $30,000 for the community.
•
The Homeless Garden Project based out of Santa Cruz, California
grows herbs, produce and flowers on its 2.5-acre plot of land. Since its
opening in 1990, the garden provides training and meaningful work
experience to less fortunate citizens in the region. Apart from the
produce that is donated to local charities, the organization sells its
vegetables, flowers and herbs wholesale and through a community
supported agriculture program. Through these sales, the garden
raises an estimated $26,000 annually (Brown, 2002).
The productivity of an urban garden depends on a number of factors: soil
conditions, irrigation, mixture of plants, and farming intensity. In a rooftop setting,
these factors are largely independent of location and can be controlled by the
gardener. Other factors, such as climate and sun exposure, are location-specific and
beyond the control of the gardener. The main constraint in terms of climate is the
duration of the growing season – i.e., the number of days between the last spring
frost and the first fall frost. In southern coastal regions, including parts of California,
22
Florida, and Texxas, outdoorr agriculturaal productioon is possiblle year roun
nd. Further
from
m the coasts and furtherr north, the growing
g
seaason becom
mes shorter (see Figure
1 for Canada). Cu
urrent climate change predictionss suggest thaat the durattion of the
grow
wing season is set to inccrease in thee cooler parrts of the continent.
Figurre 1 ‐ Duratio
on of Growing Seasons in Canada
Source: The Atlas of Canada (atlaas.nrcan.gc.ca))
Tablee 4 below su
ummarizes key informaation from tthe examplees above thaat included
moneetary valuess for agriculltural or horrticultural ooutput.5 To the data tak
ken from the
exam
mples, we haave added th
he duration of the grow
wing season
n for each location and
we have standarrdized all monetary
m
vallues to be in
n 2008 Canaadian dollarrs. To be ablle
nt sizes and in differentt climates, w
we have
to compare dataa on gardenss of differen
calcu
ulated the mean
m
producctivity per unit
u of area p
per month o
of growing season. Thee
data suggest thaat the produ
uctivity of ou
utdoor rooft
ftop gardenss ranges bettween
000 and $20
00,000 per hectare
h
per growing m
month. It app
pears that m
mixed fruit
$20,0
and vegetable
v
gaardens are at
a the low end of the prroductivity range whilee gardens
focussed more on
n flowers, heerbs, and lettuces are aat the higher end.
Table
e 4 ‐ Producttivity of urban agricultu
ure (selected
d examples)
City Area A
(h
ha) wing Grow
seaso
on (mon
nths) Outpu
ut type A
Annual output ($*/year) Produ
uctivity ($/mo
onth•ha) This table
t
brings tog
gether at-grade and rooftop gaarden informati on. We assume that rooftop gaardens have
yields similar to at-grrade gardens un
nder similar con
nditions.
5
2
23
Vancouver, BC 1.000 Vancouver, BC Berkeley, CA Newark, NJ 0.020 0.162 0.007 Santa Cruz, CA 1.012 Assorted highly 8 perishable vegetables 8 Herbs 12 Gourmet lettuces 6 Vegetables Vegetables, 12 flowers, herbs 170,100 to 216,400 24,200 28,300 to 34,000 370,000 to 444,000 ~1,000 194,700 209,400 23,800 ~38,500 38,000 * Converted to 2008 CAD.
We propose the value of the food production benefit be estimated using the
following formula:
b = P⋅ g⋅ a
Where:
•
b = annual value of benefit ($/year)
•
g = duration of the growing season (months)
•
P = productivity ($/m2•month)
•
a = green roof area (m2)
Low scenario (mixed fruits and vegetables) b =($2/m2 ⋅ month)⋅ g⋅ a
High scenario (lettuces, herbs, & flowers) b =($20/m2 ⋅month)⋅ g⋅a
3.4 Sound Attenuation Vegetated surfaces provide important sound insulation properties, especially in
urban environments where hard surfaces such as pavement and buildings tend to
reflect noise. Plants and trees tend to absorb high-frequency sounds, which are the
most bothersome to human-ear, and are often employed for their noise reduction
potential in urban settings. Although the vegetated surface of other green
infrastructure elements can provide noise reduction benefits, most of the available
data pertains to green roofs (Navrud, 2002). Green roofs can provide important
noise reduction opportunities for buildings, especially for those under flight paths
or elevated transit systems.6 Hedonic pricing and contingent valuation
6 Less directly, by decreasing heat exchange between the building and the environment and by mitigating the
heat island effect, green roofs can reduce the use of air conditioning, a source of noise.
24
methodologies have both been employed to assess the social costs of noise and
estimate values for noise reduction measures such as green roof implementation.
In a study commissioned by the European Union, Navrud (2002) attempted to
establish interim values for noise reduction from different transportation modes
(air, road, rail) by performing an extensive literature review of noise valuation
studies. The economic values attributed to road and air noise level reductions
ranged substantially from study to study, depending on the valuation method
employed (e.g., hedonic pricing or contingent valuation). Based on stated
preferences techniques, the author found that the average willingness-to-pay for
reduction in road traffic noises ranged from €2 to €32 (3 to 45 $CAN) per
household per dB per year.7 Too few stated preferences studies for aircraft noise
had been conducted to narrow the large range of willingness-to-pay in the
literature.
When using the hedonic pricing technique, the cost of noise is measured by the
Noise Sensitivity Depreciation Index (NSDI), which represents the average
percentage decrease in total property value per 1-decibel increase in noise level
above a baseline level. Typically, the cost of aircraft and road noise pollution is
calculated above a 55 dB baseline. This implies that noise levels below this
benchmark do not cause any depreciation of property value. Bateman et al. (2000)
have compiled lists of NSDIs for road traffic and air traffic noise based on the
findings of studies from the US and abroad. Road traffic NSDIs range between 0.08%
and 2.22% of property value per decibel and air traffic NSDIs range between 0.29%
to 2.3% of property value per decibel. Statistical analysis of these results showed an
average NSDI of 0.64% for road traffic pollution and 0.33% for air traffic pollution.
Navrud (2002) reports that NSDIs will be higher where households are relatively
wealthy or where levels of sound pollution are relatively higher.
Noise valuation estimates generated by hedonic pricing and contingent valuation
techniques can help to quantify the noise reduction benefits of green roofs. To date,
few research studies have estimated the noise reduction potential of green roofs.
However, Connelly & Hodgson (2008) examined the sound transmission loss of two
green roofs, one with a 75 mm substrate and the other with a 150 mm substrate.
The authors report a transmission attenuation of 5 dB to 13 dB over the low- to midfrequency range (50Hz to 2000 Hz). In the higher frequency, range transmission
attenuation ranged between 2 dB to 8 dB.
Sound attenuation provided by a green roof will depend on the properties of the
chosen substrate and on the substrate’s thickness. In the absence of data on the
noise attenuation properties of different substrates with different thicknesses, we
7 Contingent valuation studies measure the willingness to pay per person, whereas Exposure Response
Functions (ERF) express the cost per household. To convert the results of a valuation study to an approximate
ERF, the results can be multiplied by the mean household size. In Europe, mean household size is 2.16 (Navrud,
2002); in the US, it is 2.6 (US Census Bureau, 2006); and in Canada it is 2.5 (Statistics Canada, 2007).
25
propose a low (5 dB attenuation) and a high scenario (13 dB attenuation) based on
Connelly & Hodgson’s (2008) findings on the sound attenuation of 75 mm and 150
mm green roof substrates. The aforementioned findings are those for low- and midrange frequencies; we assume that most ambient noise in an urban setting falls into
this category. We assume that a green roof would primarily reduce noises from
overhead sources, such air traffic and elevated roadways and trains; it would have
little or no effect on street level traffic noise. Thus, the benefit would only accrue to
properties affected by overhead noise. Based on the findings of Bateman et al
(2000), for properties near airports or under airport flight paths, we propose using
an NSDI of 0.33%; for properties near elevated roadways or railways that are above
roof level, we propose using an NSDI of 0.64%.
We also assume that a green roof would only affect noise levels only on the top floor
of the building. We therefore assume that only the portion of the property value
represented by the top floor increases in value. For the purpose of estimation, we
assume that each floor is worth an equal portion of the total property value. Hence,
the value of the top floor is the total property value divided by the number of
storeys.
We propose the value of the sound attenuation benefit be estimated using the
following formula:
v
b = NSDI ⋅ n⋅
h
Where:
•
b = value of benefit ($/year)
•
NSDI = noise sensitivity depreciation index (/dB)
•
n = green roof sound attenuation (dB)
•
h = building height (storeys)
•
v= property value ($)
Low attenuation scenario for air traffic v
b = (0.0033/dB)⋅(5dB)⋅ ⋅
h
v
= 0.0165⋅
h
26
High attenuation scenario for air traffic b = (0.0033/dB)⋅(13dB)⋅
= 0.0429⋅
v
h
v
h
Low attenuation scenario for elevated road and rail b = (0.0064/dB)⋅(5dB)⋅
= 0.032⋅
v
h
v
h
High attenuation scenario for elevated road and rail b = (0.0064/dB)⋅(13dB)⋅
= 0.0832⋅
v
h
v
h
3.5 Stormwater Retention Vegetated surfaces have the capacity to absorb and retain stormwater, reducing the
amount of runoff. When located at-grade, vegetated surfaces absorb stormwater and
allow some of it to infiltrate into the ground or slowly release it after storm events.
Vegetated surfaces on rooftops can also retain considerable amounts of stormwater
and reduce peak flows into the stormwater system during storm events.
Less peak runoff means that new, conventional stormwater retention and
conveyance systems can have a smaller capacity or existing systems can support
more development before being upgraded, which translates to lower capital
expenditures for developers or municipalities, depending on who pays for new
stormwater infrastructure in the given context. Municipalities also stand to derive
ongoing benefits in terms of reduced operating costs related to storm management
infrastructure – less infrastructure means lower operating costs. Reducing the peak
volume of runoff and increasing on-site re-absorption of stormwater helps to
prevent water pollution. As runoff washes over various surfaces, especially
impermeable surfaces such as road and parking, it picks up particles and various
pollutants, which without mitigating measures end up draining into and polluting
local waterways. Thus, by reducing the volume of runoff, green roofs can at least
partially obviate pollution control measures. By reducing the amount of stormwater
conveyed off-site, which causes additional swelling of local bodies of water during
27
storm events, green roofs can also at least partly obviate the need for erosion
mitigation measures.
In a recent lifecycle cost-benefit analysis of green roofs, Carter and Keeler (2008)
looked at the financial dimensions of several benefits, including stormwater
management. They estimated the costs and benefits per square meter of an
extensive green roof, with a 7.62 cm (3 inch) layer of growing media, assuming a 40year reroofing cycle. The test site for which the estimates are calculated is the
Tanyard Branch watershed, which covers much of the central area of Athens,
Georgia. The test site has 53.8 % impervious land cover, with rooftops accounting
for 15.9% of the total land cover. Data on the water retention capacity of the green
roof was obtained from a test plot located on a rooftop on the University of Georgia
campus. The 7.62 cm vegetated layer assumed in the test scenario can hold 4.27 cm
of rainfall (or 42.7L of water per m2 of roof). Published retention and one-time cost
data for stormwater best management practices (BMPs) (EPA, 1999) is used to
determine the cost for an equivalent amount of rainwater retention at-grade given
the available land cover in the watershed. A combination of bioretention areas,
porous pavement, and sand filters would cost US$212.15/m3 of runoff treated,
assuming an equal distribution of these three BMPs. The avoided cost is therefore
US$9.06/m2 of green roof.
Cunningham (2001, Chapter 5) explores a theoretical scenario in which extensive
green roofing is implemented on a site containing mostly large, low-rise commercial
and industrial buildings in the City of Winnipeg. The purpose of the exercise is to
explore potential avoided costs for conventional stormwater infrastructure. The test
site has an area of 43.06 acres (17.4 ha), while flat roofs cover 10.76 acres (4.4 ha).
The study site was subdivided into three zones, each having a distinct pattern of
land use. The total runoff in the site was calculated to be 60.77 cubic feet per second
(cfs) (1.721 m3/s) for a 5-year storm; 80.25 cfs (2.272 m3/s) for a 20-year storm;
and 91.17 cfs (2.582 m3/s) for a 50-year storm. Under the test scenario, roofs in the
test site were extensively greened and assumed to have a run-off coefficient of 0.40,
as compared to a coefficient of 0.95 for flat gravel roofs. The runoff from the roofs
themselves was reduced by 58%. Site wide, this yielded a 17% reduction in the total
volume of runoff.8
Based on estimated reductions in stormwater runoff volume, reductions in the
diameter of drainage pipes required to convey runoff were calculated. In one of the
three land use zones, it was estimated that pipes could be reduced from 48 inches to
42 inches under the green roof scenario; from 42 inches to 36 in the second of three
zones; and would remain the same in the third of three zones. The author obtained
per meter cost estimates to install different diameters of drainage piping in a
development site and used these to estimate the cost of servicing the test site under
Roofs account for only a fraction of the total area of the site – i.e., 4.4 ha of 17.4 ha. The reduction in runoff
occurred only on the roofs; the volume of runoff remains the same elsewhere. Hence, site wide, the overall
reduction is much smaller than it is on the roofs themselves.
8
28
existing conditions and the green roof scenario. On this basis, it was estimated that
the latter would yield one-time material cost savings of 10% for stormwater
drainage infrastructure.
Cunningham also compared the cost of building conventional stormwater retention
infrastructure – i.e., subgrade retention basins and stormwater retention ponds –
with the cost of retaining stormwater with extensive green roofing. The cost of
retaining water with green roofing is estimated to be $14.41 per cubic foot
($508.88/m3). The cost is $30.00 per cubic foot ($1,059.44/m3) for an underground
retention basin and $0.57 per cubic foot ($20.13/m3) for a retention pond, not
including the cost of land and maintenance costs. Thus, Cunningham concludes that,
in terms of water retention, green roofing is about half as expensive as underground
retention basins. According to his calculation, stormwater retention by means of
extensive green roofing is about 25-fold more expensive than using a conventional
stormwater retention pond.9
Clark et al (2008) valuate stormwater benefits of green roofs in terms of stormwater
fee reductions accrued to property owners.10 In Ann Arbor, MI, which Clark et al use
as a case study, the stormwater fee is US$0.28 /m2 per year for impervious surfaces.
As the City of Ann Arbor considers a green roof to be a pervious surface, the annual
benefit accrued to commercial property owners is US$0.28 for every square meter
of green roof they add. The average stormwater fee charged by 11 municipalities in
the US is US$0.17/m2 per year for impervious surfaces and US$0.08/m2 per year for
green roofs. Thus, on average, property owners save US$0.09 annually in
stormwater fees for every square meter of green roof they add.
The City of Waterloo (2005), in a report on the feasibility of green roofs, valuated a
number of related costs and benefits. In its calculations, the City assumed that
stormwater management, whether by means of conventional infrastructure or a
green roof, helps control both the quantity and the quality of runoff. In terms of
quantity, stormwater management infrastructure reduces the volume of runoff by
retaining and storing a certain amount of stormwater. Assuming that conventional
stormwater storage infrastructure costs C$42/m3 and that an extensive green roof
holds 37L/m2, it was estimated that the stormwater retention benefit provided by
green roofs is worth C$1.56/m2.
In terms of quality of the runoff, the City of Waterloo estimated that, at a cost of
C$42/m3 of stormwater, conventional stormwater infrastructure for pollution
This does not factor in land costs, which could be significant. For greenfield development in the periphery of a
city, land costs can be so low that retention ponds can indeed be quite inexpensive. However, in already
urbanized areas, land costs would most likely render retention ponds prohibitively expensive, making green
roofs a viable alternative.
9
Some municipalities in North America assess stormwater fees, independent from fees or taxes for water and
wastewater services. In some cases, the municipality provides stormwater fee discounts to property owners
who implement recognized forms of on-site stormwater management, including green roofs.
10
29
control costs C$0.55/m2 (C$5,460/ha) of serviced land. Assuming that green roofs
reduce pollutant loading in stormwater by 90%, the one-time value of the runoff
quality benefit is C$0.49/m2 (C$4,914/ha). However, the authors point out that the
values for the retention and pollutant reduction benefits are not additive because
stormwater management infrastructure provides both benefits simultaneously.
Therefore, only the benefit with the higher value is considered.
The erosion reduction benefit, in contrast, is considered separately in the study.
Based on calculations made by the City of Mississauga, the City of Waterloo
estimated that conventional stormwater management infrastructure related to
erosion control requires a one-time expenditure of C$0.51/m2 (C$5,055/ha) of
developed land. Thus, assuming that extensive green roofs provide an equivalent
service, the one-time value of the erosion control benefit is C$0.51/m2 of green roof,
in addition to the other one-time stormwater benefits.
Banting et al (2005) use the pollutant reduction and erosion reduction benefits
calculated by the City of Waterloo to estimate the one-time value of stormwater
benefits accrued to the City of Toronto if all of its flat rooftops (4,984 ha) were
extensively greened. For the value of stormwater retention, they use their own
estimates, which range from C$0.95/m2 to C$26.42/m2. The estimates are based on
the cost of providing equivalent stormwater retention using the cheapest up to the
most expensive BMPs. They use the same values for pollutant reduction
(C$0.55/m2) and the same erosion mitigation (C$0.51/m2) values as the City of
Waterloo. However, they discount pollution mitigation provided by green roofs by
50% rather than by 10%, as the City of Waterloo did and they consider the pollution
benefit to be independent of the other benefits and therefore additive. The total
value of the benefit, which is a sum of the retention, pollution mitigation and erosion
control benefits, is in the range of C$1.73/m2 and C$27.20/m2. If all 4,984 ha of flat
rooftops in Toronto were extensively greened, a one-time benefit worth
C$41,800,000 and C$118,000,000 in avoided infrastructure costs would accrue to
the City.
To calculate the combined one-time value of the stormwater benefits provided by
green roofs, we follow the methodology established by the City of Waterloo. Thus,
we take the combined value of the benefit to be the higher value of either the
stormwater retention service or the pollution mitigation service, plus the value of
the erosion mitigation service provided by green roofs. From the literature
reviewed above, we have figures for the cost of three types of stormwater retention
infrastructure, including: a surface storm water retention pond, valuated at
$20.13/m3 of stormwater; mixed at-grade BMPs, valuated at $212.15/m3 of
stormwater; and an underground retention basin, valuated at $1,059.44/m3 of
stormwater. For the surface retention pond, the figure cited here presumably
applies to a greenfield development on the periphery of Winnipeg where land is
likely to be relatively inexpensive. In tighter land markets, the cost of a surface
retention pond could be considerably higher; for development in dense urban
locations, the cost could be prohibitive. We will therefore consider the
30
aforementioned cost as the lowest possible cost for stormwater retention; this
figure will be used to calculate the lower bound of the value of this green roof
benefit. Based on the data taken from the City of Waterloo study, which assumed
that a green roof retains 37L/m2, we calculate that pollution mitigation is worth
C$13.28/m3 while erosion control is worth C$13.66/m3. Given that the lowest value
for stormwater retention services cited in the literature reviewed here is
C$20.13/m3 for a retention pond, as calculated by Cunningham (2001), it appears
that the retention service will always be more valuable than the pollution removal
service. As a result, we can ignore the value pollution removal benefit in our
calculation of the total value stormwater benefits provided by green roofs.
The values per unit of area of the green roof of the stormwater services that we are
considering depend critically on the water retention capacity of the green roof. For
estimation purposes, we will assume an average retention capacity of 42.7L/m2roof,
as used by Carter and Keeler (2008), which we take to be a typical figure for an
extensive green roof.
We propose the value of the storm water retention benefit be estimated using the
following equation:
b =(R + E)⋅ C ⋅ a
Where:
•
b = value of benefit ($)
•
R = stormwater retention cost ($/m3water)
•
E = erosion mitigation cost ($/m3water)
•
C= average green roof retention capacity (m3water/m2roof)
•
a = green roof area (m2roof)
Low‐cost stormwater retention infrastructure scenario For the purpose of estimating the lower bound of the stormwater retention benefit,
we employ Cunningham’s (2001) calculation for the cost of a retention pond, the
least expensive type of retention system, barring land costs.
b =[($20.13/m3water )+ ($13.66/ m3water )]⋅(42.7m3water /m2roof )⋅ a
=[$33.79/m3water ]⋅(0.0427m3water / m2roof )⋅ a
= $1.44/ m2roof ⋅ a
31
High‐cost stormwater retention infrastructure scenario For the purpose of estimating the upper bound of the stormwater retention benefit,
we employ Cunningham’s (2001) calculation for the cost of an underground
retention basin, the most expensive retention solution of among those explored
above.
b =[($1,059.44/ m3water )+ ($13.66/ m3water )]⋅(42.7m3water / m2roof )⋅ a
=[$1,073.10/ m3water ]⋅(0.0427m3water / m2roof )⋅ a
= $45.82/ m2roof ⋅ a
3.6 Air Quality Improvement Vegetation in urban areas affects air contaminant levels and therefore has an impact
on air quality. Green plants absorb gaseous pollutants through their leaf stomates
(pores). The gases then react with water to form acids and other chemicals.
Vegetations can also capture some of the particulate matter in the air. By mitigating
the heat island effect, urban vegetation can further help reduce smog given that
higher temperatures favour smog formation. Smog is formed when nitrogen oxides
react with volatile organic compounds that are released due to the combustion of
fossil fuels; high temperatures accelerate this process. Thus, urban vegetation offers
three distinct benefits in terms air quality: reduction of gaseous pollutant, reduction
of solid particulate pollutants, and inhibition of smog formation.
Air pollution’s impacts on human health entail significant albeit indirect costs.
According to the Ontario Medical Association (OMA) (2000), air pollution related
health problems have the following economic consequences: (1) cost to the health
care system; (2) cost due to lost productivity in the workplace; (3) economic value
of pain and suffering due to pollution induced illnesses; and (4) economic damages
associated with premature death. As the OMA points out, the first two are out-of
pocket expenses for taxpayers. The air pollution mitigating benefits of green roofs
and other green infrastructure therefore accrue to society at large in the form of
avoided health care costs.
In the 1990s, the New York State Utilities Commission estimated the health care
costs attributable to several atmospheric pollutants, including nitrogen dioxide
(NO2), sulfur dioxide (SO2), carbon monoxide (CO), particulate matter of 10
micrometers or less (PM10), and ozone (O3) (Kowal, 2008) (see Table 5). These
estimates were incorporated into the Urban Forests Effects (UFORE) computer
model to calculate the value of the pollution removal benefit provide by trees and
other vegetation in urban areas. The UFORE model was developed to calculate the
pollution removal capacity of urban vegetation, and its monetary value. Pollution
removal calculations, or downwardpollutantflux, consider several factors. The key
factors are pollutant deposition velocity, which is related to wind, and the
concentration of pollutants at the given location. Other factors include the length of
32
the in-leaf season, levels of precipitation, temperature and other meteorological
variables (Nowak and Crane, 1998).
Table 5 ‐ Costs of selected atmospheric pollutants Pollutant Nitrogen Oxide (NOX) Sulfur Dioxide (SO2) Carbon Monoxide (CO) Particulate Matter <10 μm (PM10) Ozone (O3) Cost (US$/ton) 6,750 1,650 950 4,500 6,750 Source: Kowal, 2008
Currie and Bass (2008) used UFORE to explore the pollution mitigating capacity of
green roofs and green walls. Field data was collected from 72 circular plots, each
400m2 and having a different distribution of vegetation, in the Midtown area of
Toronto. The data was fed into the UFORE model to estimate the 03, S02, N02, C0 and
PM10 removal capacity of the current vegetation in the study area, to be used as a
baseline scenario, and that of six hypothetical vegetation scenarios. The hypothetical
scenarios either added new vegetative elements to the study area, such as green
walls (i.e., juniper hedges), extensive and intensive green roofs, or subtracted
existing vegetative elements, such as trees and shrubs. The difference between the
baseline scenario and each hypothetical scenario was taken to be the pollution
mitigating capacity of the individual vegetative element that was added or removed
in the given scenario.
The key findings of the study were that, while trees clearly have a greater pollution
mitigating capacity, shrubs and grasses, which can be readily planted on flat
rooftops, can nonetheless have a very substantial effect on air pollution and a
significant monetary value. Covering all flat rooftops, equivalent to about 20% of all
roof surfaces in the study area, with a grassy vegetated surface would augment the
pollution mitigation provided by existing trees and shrubs by as much as 10% and
be worth US$17,481 a year in terms of avoided healthcare costs. Based on the
results of Currie and Bass’s study, Banting et al. (2005) calculated the annual
monetary value of extensive green roofs in Toronto to be about US$0.0394/m2
(C$0.0541/m2 in 2008) of extensively vegetated roof area. If all flat rooftops across
the City of Toronto (4984 ha) were extensively greened, the annual cost savings
attributable to reduction in air pollution would amount to US$1,970,000
(C$2,700,000 in 2008).
Yang, Yu and Gong (2008) quantified the volume of air pollution mitigation provided
by green roofs in Chicago. They obtained detailed data on 71 out of some 170 green
roofs, totaling 19.8 ha. Aerial photographs of the roofs were analyzed to determine
the distribution of different types of surfaces on the green roofs. It was found that
63% of the green roofs’ aggregated area consisted of short grasses, 14% of large
herbaceous plants, 11% of trees and shrubs, and the remaining 12% of various
structures and hard surfaces. A pollutant deposition model for big-leaf plants
employing atmospheric data collected in Chicago over a one-year period were used
33
to estimate the absorption of four principal air pollutants (SO2, NO2, PM10, and O3)
by each of the three observed types of vegetation (summarized in Table 6). Yang, Yu
and Gong’s (2008) results can be combined with the health cost data cited by Kowal
(2008) to calculate the value of the pollution mitigation provided by each type of
plant (see Table 7).
Table 6 ‐ Annual pollutant removal by different types of green roof vegetation in Chicago (g/m2∙year) Type of vegetation SO2 N02
PM10
O3
Total Short Grass Tall Herbaceous Plants Deciduous Trees 8.59 11.1 13.91 0.65 0.83 1.01 2.33 2.94 3.57 1.12 1.52 2.16 4.49 5.81 7.17 Source: Yang, Yu and Gong, 2008
Table 7 ‐ Value of annual pollutant removal health benefit for different types of green roof vegetation (US$/m2∙year) Type of vegetation
Short Grass
Tall Herbaceous Plants
Deciduous Trees
SO2
0.0010725
0.0013695
0.0016665
N02
0.0157275
0.0198450
0.0240975
PM10
O3
0.00504
0.00684
0.00972
Total
0.0303075
0.0392175
0.0483975
0.0521
0.0673
0.0839
Combining data from Yang, Yu and Gong (2008) and Kowal (2008)
As suggested by the studies cited above, the critical determinants of a green roof’s
capacity to mitigate pollution and yield health benefits include its area and the mix
of plant species that is used, as some species absorb more pollutants than others.
Other factors include the levels of air pollution at the given location and the climate.
In terms of the latter, the pollution mitigation provided by the green roof may be
limited outside the growing season, particularly if it is covered with snow. The
examples above, from Toronto and Chicago, estimate pollution mitigation of green
roofs in locations with relatively short growing seasons (about seven months) and
long, snowy winters. In places with a longer growing season, the annual volume of
pollution absorbed is likely to be higher given the same plant species. We take a
seven-month growing season to be the baseline case.
Using the values for the pollutant removal health benefit that we have calculated
using Yang, Yu and Gong’s (2008) and Kowal’s (2008) findings (Table 7), we
propose the following formula for estimating the annual value of the health benefit
of pollution mitigation provided by green roofs:
g
b=
⋅[H sg ⋅ asg + Htg ⋅ atg + Hd ⋅ ad ]
7⋅ months
Where:
•
b = value of benefit ($/year)
•
g = growing season (months)
34
•
Hsg = health benefit for short grass pollution absorption ($/m2•year)
•
asg = green roof area covered by short grass (m2)
•
Htg = health benefit for tall grass* pollution absorption ($/m2•year)
•
atg = green roof area covered by tall grass* (m2)
•
Hd = health benefit for deciduous plant pollution absorption
($/m2•year)
•
ad = green roof area covered by deciduous plants (m2)
*tall herbaceous plant
Using the annual pollutant removal values cited in Table 7, we obtain:
g
b=
⋅[($0.0521/m2 )⋅ asg + ($0.0673/m2 )⋅ atg + ($0.0839/m2 )⋅ ad ]
7⋅ months
The above equation can only be applied if the distributions of the three categories of
vegetation within the green portion of the roof are known. If the distribution is
unknown, the estimate will lie somewhere between a lower bound defined by a
green surface area composed entirely of short grass (the least absorbent) and an
upper bound defined by a green surface composed entirely of deciduous plants (the
most absorbent).
Low scenario (100% short grass coverage) g
⋅[($0.0521/m2 )⋅(a)+ ($0.0673/m2 )⋅(0)+ ($0.0839/m2 )⋅(0)]
7⋅ months
g
⋅[($0.0521/m2 )⋅ a + 0+ 0]
=
7⋅ months
2
= ($0.0074/m ⋅ months)⋅ g⋅ a
b=
Where:
a = area of the green roof (m2)
35
High scenario (100% deciduous tree coverage) g
⋅[($0.0521/m2 )⋅(0)+ ($0.0673/m2 )⋅(0)+ ($0.0839/m2 )⋅(a)]
7⋅ months
g
⋅[0+ 0+ ($0.0839/m2 )⋅ a]
=
7⋅ months
2
= ($0.0120/m ⋅ months)⋅ g⋅ a
b=
Where:
•
a= area of the green roof (m2)
3.7 Greenhouse Gas Sequestration Carbon dioxide is the most common greenhouse gas and its rising levels in the
atmosphere are believed to contribute to global warming. Reducing emissions of
carbon dioxide and capturing the carbon dioxide that is already in the atmosphere
are increasingly being pursued as strategies to mitigate global warming.
All photosynthesizing plant species have the capacity to capture and store
atmospheric carbon dioxide (CO2). Trees and other plants in urban environments
are no exception. Thus, a further benefit of green roofs and other green
infrastructure is their ability to capture and store – i.e., sequester – carbon dioxide.
Valuating the carbon dioxide sequestration benefit of green infrastructure entails
estimating the marginal social cost of damages that would have been caused due to
temperature increases if not for the sequestration carried out by the vegetation
involved.
Most studies on carbon dioxide sequestration provided by plants have focused on
trees. Nowak and Crane (2002) assess the carbon sequestration capacity of urban
trees across the US. The authors determined that there were approximately 281,000
km2 of urban tree cover across the US, storing 700 million metric tones of carbon
and annually sequestering 22.8 million tons. The carbon storage and annual carbon
uptake provided by urban trees are valued at US$14.3 billion and US$460 million
per year, respectively. Based on these estimates, the average value of carbon storage
by urban trees would be approximately $510/ha for stored carbon and $16/ha for
annual carbon uptake. The authors note that carbon storage and uptake are lower in
urban than non-urban tree stands because the density of the tree cover is generally
much lower. On average, urban trees store 25.1 tonnes/ha of carbon whereas forest
stands store 53.5 tonnes/ha – more than twofold as much. Urban trees sequester on
average 0.3 tonnes/ha per year while natural growth tree stands sequester 1.0
tonnes/ha per year and tree plantations sequester as much as 2.6 tonnes/ha per
year.
36
In a recent report, the David Suzuki Foundation (2008) examines a number of
ecosystem services provided by the Greater Golden Horseshoe Greenbelt in
southern Ontario, including carbon sequestration. Among other benefits, the annual
carbon sequestration values for different biomes within the greenbelt are estimated
(see Table 8). Carbon sequestration per hectare, in terms of both annual uptake and
total storage, 11 is calculated for the different biomes in the Greenbelt using a
software package called CITYgreen (similar to UFORE). To convert these
sequestration capacities to monetary values, the author assumes a cost of
$43/tonne (2005 US dollars) for global damages due to carbon dioxide levels in the
atmosphere. This value is based on the average cost of global damages due to the
level of carbon dioxide in the atmosphere in 2005, as reported by the
Intergovernmental Panel on Climate Change (IPCC) (2007).
Table 8 ‐ Carbon sequestration values per hectare for Greater Golden Horseshoe Greenbelt land types Stored carbon Annual carbon uptake Forest Grassland Agricultural Lands Cropland Idle land Hedgerows Orchards $919 $213 $332 $317 $328 $298 $39.11 $28.46 N/A $28.59 $28.59 $28.59 Source: David Suzuki Foundation, 2008
While the aforementioned studies focus on the sequestration of atmospheric carbon
provided by trees and other vegetative covers, other studies have explored indirect
carbon dioxide emissions reductions provided by green infrastructure. Akbari and
Konopacki (2003) calculated that mitigation of the urban heat island effect provided
by trees and green infrastructure could reduce building carbon emissions by 5-20
percent. A number of authors have noted that green roofs produce energy savings
by reducing heat exchange through the roof, resulting in lower energy use for
heating in the winter and air conditioning in the summer. A recent paper by The
Trust for Public Land (2008 b) on the greenhouse gas benefits of urban parks
suggest other indirect energy saving benefits that could also apply to green roofs.
The authors suggest that urban parks can reduce the amount of energy used to
manage stormwater runoff. This is especially likely to be true in communities that
do not have separate stormwater sewer systems and send stormwater mixed with
regular wastewater through energy consuming sewage treatment plants. It is also
suggested that some GHG emission reductions can result from reduced
transportation use, given that the provision of parks (or accessible rooftop gardens)
can provide more accessible leisure opportunities.
The indirect carbon dioxide emissions reductions, though potentially significant,
would be very difficult to valuate. Most depend on factors that could vary
significantly from place to place and could be difficult to determine without a
substantial research effort. For instance, the extent of emission reductions achieved
Annual carbon uptake is a measure of the average amount of carbon sequestered per year by given plant or by
a vegetated area. Carbon storage is the total amount of carbon sequestered over a longer period – for an
individual plant, over its lifetime.
11
37
by reducing energy use depends crucially on how much of the local energy supply is
fossil fuel based. For this reason, we do not attempt to devise a method for valuating
the indirect benefits of CO2 emissions reductions afforded by green roofs; we
restrict our method to valuating direct carbon sequestration.
Our formula for estimating the value of sequestered carbon is based on the findings
of the David Suzuki Foundation (2008). We chose these findings because they
provide sequestration values for types of vegetation other than forests, namely
grassland and croplands, both of which are more likely to be found on a green roof
than trees. We assume that the annual carbon uptake of these types of vegetation is
the same on a green roof as at grade. As the methodologies reviewed estimate the
sequestration value of trees on a large scale basis (square kilometres or hectares),
and because the values are relatively small, we use hectares rather than meters as
units of area.
We propose the following formula for calculating the value of annual carbon
sequestration provided by a green roof:
b = Sdad + Sgag + S f a f
Where:
•
b = value of benefit ($/year)
•
Sd = value of carbon sequestration by deciduous plants ($/ha•year)
•
ad = area of green roof covered by deciduous plants (ha)
•
Sg = value of carbon sequestration by grasses ($/ha•year)
•
ag = area of green roof covered by grasses (ha)
•
Sf = value of carbon sequestration by productive agriculture
($/ha•year)
•
af = area of green roof covered by productive crops (ha)
Note:
ag = asg + atg
•
asg = area of green roof covered by short grasses (ha)
•
atg = area of green roof covered by tall grasses (ha)
38
Using the David Suzuki foundations sequestration data, and assuming that
productive agriculture on green roofs resembles hedge rows or orchards, we obtain:
b =($39.11/ ha)ad +($28.46/ ha)ag +($28.59/ ha)a f
Low scenario (100% grass coverage) b = ($39.11/ ha)(0)+ ($28.46/ ha)(a)+ ($28.59/ ha)(0)
= 0+ ($28.46/ ha)⋅ a + 0
= ($28.46/ ha)⋅ a
Where:
•
a = area of the green roof (ha)
High scenario (100% deciduous coverage) b = ($39.11/ ha)(a)+ ($28.46/ ha)(0)+ ($28.59/ ha)(0)
= ($39.11/ ha)⋅ a + 0+ 0
= ($39.11/ ha)⋅ a
Where:
•
a= area of the green roof (ha)
39
4 Case Studies The last section provided valuation methodologies that could be used to quantify
several of the “soft” benefits associated with green roofs. In the following section,
we apply these methodologies to five case studies in order to estimate the actual
benefits associated with these green roofs under realistic conditions. The
information for these scenarios is drawn from sources such as Steven Peck's book
AwardWinningGreenRoofDesigns(2008), project web sites, and interviews with
architects and developers.
The case studies were chosen in order to represent a variety of building types and
locations. Together, they provide opportunities for the use of all the calculation
methods presented in Section 3 of this report. Not all of the benefits apply to each
case study; only those benefits that apply to each case study and for which data was
available are included in the write-ups.
For each case study, we present key features of the project and associated green
roof, a summary of the development context and process, and the benefit
calculations themselves. We conclude each case study with some observations about
the calculations, which are designed to help the reader interpret the results.
The case studies use a consistent notation to signify variables that go into the
calculation of benefits. Table 18 summarizes the variables needed as inputs into the
equations and the notation used in the case studies.
40
Table 9 ‐ List of benefits, input variables, notations, and units benefit
input variable notation unit
property value (recreational garden)
property value
v dollars
property value (productive garden)
neighbouring property value
vn dollars
neighbouring property distance
dn meters
property value (property with view)
property with view value
vv dollars
property with view height
hv meters
green roof height
h stories
growing season
g months
food production area
af square meters
actual value of food production
vf dollars
property value
v dollars
building height
h stories
stormwater retention
vegetative roof area
a square meters
air quality
growing season
g months
vegetative roof area (total)
a square meters
short grass area
asg square meters
tall grass area
atg square meters
deciduous plant area
ad square meters
vegetative roof area (total)
a square meters
food production area
af square meters
grass area (short + tall)
asg + atg square meters
deciduous area
ad square meters
food production
sound attenuation
GHG sequestration
41
4.1 Case Stud
dy 1 – 901 Cherry Avvenue, San
n Bruno, CA
A 4.1.1 Key Featu
ures location type of building numb
ber of storeyys type of green roo
of roof cconstruction
n comp
pletion date developer desiggner vegettative area depth
h of growingg medium type of vegetatio
on accesssibility 901 Cherrry Avenue, SSan Bruno, CA
office buillding
3 semi‐exte
ensive
new consttruction
1997
GAP Inc.
William M
McDonough ++ Partners
6,400 m2 (69,000 sq ftt)
15.2 cm (6
6”)
native graasses and wi ldflowers
inaccessib
ble
4.1.2 Summaryy of Project The 901
9 Cherry Avenue buiilding housees offices off the clothin
ng maker GA
AP Inc. The
build
ding was com
mmissioned
d by GAP ab
bove all to bee a high quaality work eenvironmen
nt
with a number of
o amenitiess, including a café and a fitness cen
ntre. The bu
uilding also
inclu
udes a numb
ber of sustaiinable desiggn features, of which th
he centerpieece is an
undu
ulating 6,400 m2 (69,00
00 sq ft) sem
mi-extensivee green rooff. The roof ffeatures a 15
5
cm (6
6”) growing
g medium pllanted with grasses and
d wildfloweers native to
o the San
4
42
Francisco Bay Area. Much liike wild graassland, the roof vegetaation is high
hly selfsustaaining, requiring minim
mal maintenance (Peck,, 2008).
A nottable featurre of the 901
1 Cherry building is thaat it is locateed under th
he flight path
h
of airr traffic land
ding at the San
S Franciscco Internatiional airporrt and, as su
uch, is
exposed to considerable ov
verhead noisse. The greeen roof helps provide an acoustic
barriier that atteenuates soun
nd transmisssion from aaircraft takiing off from and landing
at thee airport.
4
43
4.1.3 Benefits Calculations benefit property value ‐ recreational rooftop garden ‐ productive rooftop garden ‐ view onto a green roof marketing applicable sound attenuation food production stormwater retention air quality GHG sequestration comment not accessible no food produced no taller building nearby data unavailable building lies under the runway flight path for the San Francisco International Airport no food produced 4.1.4 Variables See Table 9 for a definition of the variables.
v
h
a
g
=
=
=
=
US$55,545,399
3 stories
6,400 m2
12 months
4.1.5 Calculations 4.1.5.1 soundattenuation
Low attenuation scenario for air traffic Since the current property value includes the sound attenuation benefit, we let:
vx = property value excluding the sound attenuation benefit ($)
44
v = vx + b
and
vx
h
therefore
b = 0.0165⋅
vx
)
h
0.0165
v = v x ⋅(1+
)
h
v
vx =
0.0165
1+
h
($55,545,399)
=
0.0165
1+
(3)
v = v x + (0.0165⋅
= $55,241,570
b = v − vx
= ($55,545,399)−($55,241,570)
= $303,829
45
High attenuation scenario for air traffic v = vx + b
and
vx
h
therefore
b = 0.0429⋅
vx
)
h
0.0429
v = v x ⋅(1+
)
h
v
vx =
0.0429
1+
h
($55,545,399)
=
0.0429
1+
(3)
v = v x + (0.0429⋅
= $54,762,298
b = v − vx
= ($55,545,399)−($54,762,298)
= $783,101
4.1.5.2 stormwaterretention
Low‐cost stormwater retention infrastructure scenario b = $1.44/ m2 ⋅ a
= $1.44/ m2 ⋅(6,400m2 )
= $9,216
High‐cost stormwater retention infrastructure scenario b = $45.82/ m2 ⋅ a
= $45.82/ m2 ⋅(6,400m2 )
= $293,248
46
4.1.5.3 airquality
Low scenario (100% short grass coverage) b = ($0.0074/m2 ⋅ months)⋅ g ⋅ a
= ($0.0074/m2 ⋅ months)⋅(12months)⋅(6,400m2 )
= $568
Note: only the low scenario is calculated as it is known that the green roof is covered
only with short grasses
4.1.5.4 GHGsequestration
Low scenario (100% grass coverage) b =($28.46/ ha)⋅ a
=($28.46/ ha)⋅(0.64ha)
= $18.21
Note: only the low scenario is calculated as it is known that the green roof is covered
only with short grasses
4.1.6 Benefits Summary benefit sound attenuation stormwater retention air quality GHG sequestration type one time one time annual annual value $303,829 – $783,101
$9,216 – $293,248
$568/year
$18/year
4.1.7 Observations ƒ The value of the sound attenuation benefit is estimated to be between
$303,829 and $783,101. The value of the benefit is likely to be in the upper
range given that the thickness of the green roof substrate is 15.2 cm. This
corresponds almost exactly to thickness of the thicker, 150 mm substrate
tested by Connelly and Hodgson (2008), which was determined to attenuate
sound by 13 dB and which is the basis for calculating the upper bound of the
value of this benefit.
ƒ
The value of the stormwater benefit is estimated to be between $9,216 and
$293,248. Given that there is relatively little precipitation in the San
Francisco Area, and given that the building is in a relatively low-density
suburban setting, conventional stormwater infrastructure would not be
47
particularly expensive in this case. Thus, the value of the stormwater benefit
is likely to be in between the bottom and middle of this range.
ƒ
The pollution mitigation and GHG sequestration benefits were estimated to
be worth $568 and $18 per year respectively. As this green roof has 100%
grass cover, only the lower bound calculation methods were used to estimate
the values of these benefits. If other types of plants were present, such as
deciduous bushes or trees, pollution mitigation and GHG sequestration
would most likely be higher.
48
4.2 Case Stud
dy 2 – Fairm
mont Waterfront Ho
otel, Vanco
ouver, BC 4.2.1 Key Featu
ures location type of building numb
ber of storeyys type of green roo
of roof cconstruction
n comp
pletion date developer desiggner vegettative area depth
h of growingg medium type of vegetatio
on accesssibility 900 Canad
da Place Waay, Vancouveer, BC hotel 23 intensive
new consttruction ivy garden
n 1991, replaaced by herb
b garden in 1994 Canadian Pacific Hoteels (now Fairrmont Hotelss) Musson C
Cattell Mackeey Partnersh
hip 2
195.1 m (2,100 sq ft)) 46 cm (18
8”) primarily herbs, somee flowers, fru
uits and vegetables accessible
e to hotel staaff and guessts 4.2.2 Summaryy of Project F
Waterfront
W
Hotel
H
is a luxxury hotel oon the down
ntown Vanco
ouver
The Fairmont
wateerfront, adjaacent to the Canada Place cruise sh
hip terminall and the Waaterfront
train
n station and
d transit terrminal. Wheen the hotel was built in
n 1991, a grreen roof
with ivy and peaa gravel path
hs was initially installeed on the larrge third flo
oor terrace
on th
he building’ss south sidee; the hotel has
h a total oof 23 storeyys. The hotell designers’
4
49
inten
ntion was to
o provide pleasant view
ws for occup
pants of the rooms on th
he south
side of the high-rise tower above
a
the teerrace; room
ms on the no
orth side already had
view
ws into the harbour and the mountaains in the d
distance. Th
he City of Vaancouver
supp
ported the crreation of th
he green terrrace, recoggnizing that it would alsso afford
pleassant views for
f the neigh
hbouring bu
uildings (CM
MHC, 2003)..
The southern
s
po
ortion of thee terrace waas converted
d to an herb
b garden in 1994 at a
cost of
o C$25,000
0. The herb garden wass implementted on the ssouth terracce because
sun exposure
e
waas not sufficcient elsewh
here. The gaarden is maintained year round
and harvested
h
between latee march and
d late fall byy the hotel’s restaurant staff. The
gardeen is divided into 11 pllant beds in which overr 60 speciess were grow
wn in the
2008
8 season. Th
he majority of
o the species grown arre herbs but the garden
n also
produces leafy green
g
vegetaables such as
a chard, aru
ugula, bok cchoy, and Ch
hinese
green
ns, as well as
a a few smaall fruits succh as strawb
berries, plum
ms, and graapes. Severaal
speciies of decorative and ed
dible plantss are grown as well (Jam
mieson, 200
08). The
produce is used primarily in
n the hotel restaurant
r
b
but consum
mers also incclude hotel
staff and patrons. The gardeen also prov
vides habitaat for a largee number of small
birdss.
Calculationss 4.2.3 Benefits C
bene
efit prope
erty value ‐ recrreational roo
oftop garden
n appliccable ‐ prod
ductive roofftop garden ‐ view
w onto a green roof comment not recreational ble to tenantts/owners off not accessib
surroundingg properties,, applies only tto the host p
property ttested on Prricewaterhouse Cooperss Place at 2500 Howe, facin
ng directly into the garden 5
50
marketing sound attenuation food production stormwater retention air quality GHG sequestration data unavailable no significant source of overhead noise 4.2.4 Variables See Table 9 for a definition of the variables.
v = C$116,078,000 vv = C$119,688,000* h = 3 stories hv = 20 stories* a = 195.1 m2 g = 8 months * PricewaterhouseCoopers Place at 250 Howe Street, directly across from the herb
garden (source: City of Vancouver)
4.2.5 Calculations 4.2.5.1 propertyvalue
Host property with productive rooftop garden Since the current property value includes the benefit, we let:
vx = property value excluding the benefit ($)
51
v = vx + b
and
b = 0.07⋅ v x
therefore
v = v x + (0.07⋅ v x )
v = 1.07⋅ v x
v
1.07
($116,078,000)
=
1.07
= $108,484,112
vx =
b = 0.07($108,484,112)
= $7,593,888
View onto a green roof: Whole building gain in property value Since the current property value includes the benefit, we let:
vnx = property value of the neighbouring excluding the benefit ($)
52
v v = vnx + b
and
a
b = 0.045⋅
hv − h
⋅ vnx
hv
therefore
t
v v = vnx + (0.045
5⋅
= vnx + (0.045
5⋅
hv − h
⋅ vnx )
hv
(20)−(3)
⋅ vnx )
(20)
v v = 1.03825⋅ vnx
n
vv
1.03825
($433,856))
=
1.03825
593
= $115,278,5
vnx =
b = v v − vnx
000)−($115
5,278,594)
= ($119,688,0
6
= $4,409,406
4.2.5..2 foodpro
oduction
Low sscenario High scenario 53
4.2.5..3 stormwaterretention
Low‐ccost stormw
water retentio
on infrastruccture scenarrio High‐‐cost stormw
water retentiion infrastru
ucture scenaario 4.2.5..4 airquallity
Low sscenario (10
00% short gra
ass coveragee) High scenario (10
00% deciduo
ous tree coveerage) questration
4.2.5..5 GHGseq
Low sscenario (10
00% grass coverage) High scenario (10
00% deciduo
ous coveragee) 54
4.2.6 Benefits Summary benefit property value (host) property value (neighbour) food production stormwater retention air quality GHG sequestration type one time one time annual one time annual annual value $7,593,888
$4,409,406
$3,121 ‐ $31,210
$281 ‐ $8,939
$11.54 ‐ $18.73
$0.56 ‐ $0.76
4.2.7 Observations ƒ The property value benefit of $7,593,888 that accrues to the hotel seems
realistic. The PricewaterhouseCoopers Place across the street from the herb
garden was calculated to receive a boost in property value on the order of
$4,409,406, also seemingly realistic.
ƒ
The production food production value was estimated to be between $3,121
and $31,210. Given that the garden produces herbs, lettuces, and flowers
primarily, all of which have a high market value, the total value of production
is likely to be at the upper end of this range.
ƒ
The stormwater management benefit is estimated to range between $281
and $8,939. Given that the building is located in an extremely dense urban
environment with very high land values, low cost stormwater management
solutions (which are land intensive) are not an option. For this reason, the
value of the benefit is likely to be at the upper end of the range in this case.
ƒ
The value of the air quality benefit is estimated to be between $11.54 and
$18.73. Given the prevalence of leafy plants, the value is likely to tend
towards the upper range.
ƒ
The GHG sequestration benefit is estimated to be worth between $0.56 and
$0.76. Given that garden includes mostly small plants and few bushes and
trees, the value of the benefit is likely to tend towards the lower end of the
range.
55
4.3 Case Stud
dy 3 – 401 Richmond
d, Toronto,, ON 4.3.1 Key Featu
ures location type of building numb
ber of storeyys type of green roo
of roof cconstruction
n comp
pletion date developer desiggner vegettative area depth
h of growingg medium type of vegetatio
on accesssibility 401 Richm
mond Streett West, Toro
onto, ON commerciial 4 semi‐inten
nsive retrofit intensive portion buil t in 1998; extensive portion addded 2005 Urbanspace Property Group intensive portion by M
Margaret Zeidler and Mo
onika Kuhn;
extensive portion by XXero Flor 603.9 m2 (6,500 sq ft)) intensive;
241.5 m2 (2,600 sq ft)) extensive;
65.0 m2 (7
700 sq ft) greeenhouse intensive portion madde up of con
ntainers of vaarious depth
h;
extensive portion is 5 cm (2”) deeep intensive portion has flowers, vin
nes, and bush
hes; extensive portion is coovered in seedum accessible
e to the geneeral public 5
56
4.3.2 Summaryy of Project The 401
4 Richmo
ond buildingg was origin
nally constru
ucted in 189
99 and housed a factorry
producing lithog
graphed tinw
ware. The building
b
wass expanded between 19
903 and
1923
3, taking on it current ‘letter A’ floo
or plan (see aerial photto below). T
The buildingg
changed hands several
s
timees in the posstwar era an
nd was slateed for demo
olition when
n
Toronto impresaarios, the Zeeidler Familly, purchaseed the build
ding. The bu
uilding
undeerwent majo
or refurbish
hment over next
n
few yeears. The building’s 18,5
580 m2
(200,000 sq ft) floor
f
area no
ow houses over
o
140 arrtists and en
ntrepreneurrs, includingg
fine artists,
a
desig
gners, millin
ners, architects, filmmaakers, gallerries, musicians, arts
organ
nizations, and magazin
nes (Urbansp
pace Properrty Group, 2
2008).
The roof garden waas informallly initiated
he third floo
or roof on
in 1995 on top of th
the soutth side (back) of the property. Thee
rooftop was alreadyy a popularr gathering
space foor the buildiing’s tenantts. The
property
ty manager, a plant aficcionado,
spearheeaded the deevelopmentt of the
garden. In 1998, a 6
603.9 m2 (6
6,500 sq ft)
nstructed on
n a portion
cedar deeck was con
of the rooof and coveered with numerous
planterss with floweers, bushes, and vines.
The species
s
werre selected primarily
p
for their decoorative value (Urbanspace
Property Group,, 2007a). A 65.0
6
m2 (70
00 sq ft) gre enhouse, w
which servess as a winterr
nts, was add
ded in 2000
0. Later, in 2
2005, a furth
her 241.5 m2
nurseery for some of the plan
(2,60
00 sq ft) of the
t roof werre covered with
w a lightw
weight exteensive green
n roof
systeem, consistin
ng of a 2-incch growing medium plaanted with sedum (Urb
banspace
Property Group,, 2007b).
4 Richmo
ond roof garrden has atttracted a con
nsiderable aamount of aattention
The 401
from
m the media in Toronto, providing publicity
p
forr Urbanspacce Propertyy Group, the
comp
pany that ow
wns and maanages the building,
b
and
d indirectlyy for the building’s
tenan
nts. In 2008
8, the City off Toronto aw
warded Urb
banspace Prroperty Grou
up a Green
Toronto Award for the 401 Richmond roof garden
n.
a Urbanspaace, residentts living in tthe 14-storeey District
According to an employee at
Loftss building, directly
d
acro
oss Richmon
nd Street, saay that they enjoy the vview onto
the 401
4 Richmon
nd roof gard
den. A group of residen
nts at District Lofts wass reportedlyy
inspiired to creatte their own
n rooftop gaarden and coontacted Urrbanspace tto obtain
inforrmation for this purposse. The initiaative has yeet to be realiized.
5
57
4.3.3 Benefits C
Calculationss bene
efit prope
erty value appliccable comment ‐ view
w onto a green roof ttested on a loft condom
minium unit at 388 Richm
mond St. Weest ‐ recrreational roo
oftop garden
n ‐ prod
ductive roofftop garden markketing sound
d attenuatio
on food production storm
mwater reten
ntion air qu
uality GHG sequestratio
on primarily reccreational; ccurrently no ffood producction no source off significant overhead noise currently no
o food produ
uction 4.3.4
4 Variabless See Table
T
9 for a definition of the variaables.
v
vv
a
g
pradio
rradio
tradio
ptv
rtv
ttv
=
=
=
=
=
=
=
=
=
=
C$13,923,000
C$296,500**
845.4 m2 (=
= 603.9 m2 + 241.5 m2)
7 months
0 note:therrehasbeenn
noknownraadiocoverag
geof401Riichmond
$250/spot fromTable 3
0
umption
$2,000 assu
$2,778/spo
ot fromTablee 3
2.3 spots seeecalculatio
onbelow
5
58
pprint = $100 assumption
rprint = 190.4 inches seecalculationbelow
l = $392/inch fromTable 3
* Sale price of a condominium loft unit at 388 Richmond West with a view onto the
401 Richmond roof garden (source: REMAX)
4.3.5 Calculations 4.3.5.1 propertyvalue
View onto a green roof: Single unit gain in property value Since the current property value includes the property view benefit, we let:
vnx = property value of the unit with a view excluding the benefit ($)
v v = vnx + b
and
b = 0.09⋅ vnx
therefore
v v = v vnr + (0.09⋅ vnx )
v v = 1.09⋅ vnx
vv
1.09
($296,500)
=
1.09
= $272,018
vnx =
b = v v − vnx
= ($296,500)−($272,018)
= $24,482
Host property with recreational rooftop garden Since the current property value includes the property value benefit, we let:
vx = property value excluding the benefit ($)
59
v = vx + b
and
b = 0.11⋅ v x
therefore
v = v x + (0.11⋅ v x )
v = 1.11⋅ v x
v
vx =
1.11
(13,923,000)
=
1.11
= 12,543,243
b = 0.11(12,771,513)
= 1,379,756
4.3.5.2 marketing
Table 10 – Media Coverage of the 401 Richmond Green Roof in Toronto TELEVISION Station Vision TV Program Recreating Eden Conv. Discount factor factor (D) Spots 1/min
0.1 2.3
Total 2.3
Type of mention factual
Dimension 23 min
Type of mention Dimension Conv. Discount factor factor (D) PRINT Source The Globe and Mail The Globe and Mail The Globe and Mail The Globe and Mail The Globe and Title "A garden rooted on the rooftop" "Zeidler combines building and activism" "The places that mattered to Jane Jacobs" "Growing an Eden up near heaven" "Growing an Eden up article 17” picture Column Inches 2 1 34” 9” X 6” 0.5 1 27.0” picture 6” X 4” 0.5 1 12.0” article 21.5” 2 1 43.0” picture
8.5” X 5”
0.5
1 21.3”
60
Mail Toronto Star Toronto Star Toronto Star Toronto Star Toronto Star Toronto Star Toronto Star near heaven" "It's easier being green"
"Rooftop relief" "Rooftop relief" "Feeling the need for green" "Office oasis" "Office oasis" "Gardens in the sky yield earthly delights" "Look up, look way up"
"Best Free Hangout"
Green Toronto Award Nominations Eye Weekly Now Magazine Green Living Magazine Green Living "A roof that's a view" Magazine Our Arts Feature Neighbourhood The Liberty "Green groceries" Gleaner Your Source “Rooftop gardens” Magazine Source: Urbanspace Property Group
sentence
article
picture
1 sentence
1”
7.5” X 4.5”
‐
2
0.5
1 1 1 1.0”
2.0”
16.9”
2 1 3.0” 2
0.5
1 1 2.0”
11.9”
article 1.5” article
picture
1”
9” X 5.5”
article 3.5” 2 1 7.0” article
article
1.5”
2.5”
2
2
0.25 0.25 0.8”
1.3”
article 2” 2 0.1 0.4” article 17” 2 0.1 3.4” picture 5.5” X 3.5” 0.5 0.1 1.0” article 3.5” 2 0.1 0.7” article 8.5” 2 0.1 1.7” Total 190.4”
b =[pradio + rradio ⋅tradio ]+[ptv + rtv ⋅ttv ]+[ppaper + rpaper ⋅ l]
=[(0)+ ($250)(0)]radio +[($2,000)+ ($2,778)(2.3)]tv +[($100)+ ($392)(190.4)]paper
= 0+ $8,389.40+ $74,736.80
= $83,126
4.3.5.3 stormwaterretention
Low‐cost stormwater retention infrastructure scenario b = $1.44/m2 ⋅ a
= $1.44/m2 ⋅(845.4m2 )
= $1,217
High‐cost stormwater retention infrastructure scenario b = $45.82/ m2 ⋅ a
= $45.82/ m2 ⋅(845.4m2 )
= $38,736
61
4.3.5.4 airquality
Low scenario (100% short grass coverage) b = ($0.0074 / m2 ⋅ months) ⋅ g ⋅ a
= ($0.0074 / m2 ⋅ months) ⋅(7months) ⋅(845.4m2 )
= $43.79
High scenario (100% deciduous tree coverage) b = ($0.0120/m2 ⋅ months)⋅ g ⋅ a
= ($0.0120/m2 ⋅ months)⋅(7months)⋅(845.4m2 )
= $71.01
4.3.5.5 GHGsequestration
Low scenario (100% grass coverage) b =($28.46/ ha)⋅ a
=($28.46/ ha)⋅(0.08454ha)
= $2.41
High scenario (100% deciduous coverage) b =($39.11/ ha)⋅ a
=($39.11/ ha)⋅(0.08454ha)
= $3.31
4.3.6 Benefits Summary benefit property value (host building) property value (neighbouring condo unit) marketing stormwater retention air quality GHG sequestration type value $1,379,756
one time one time $24,482
one time one time annual annual $83,126
$1,217 ‐ $38,736
$43.79 ‐ $71.01
$2.41 ‐ $3.31
62
4.3.7 Observations ƒ The property value benefit of $1,379,756 that accrues to the owner of 401
Richmond seems realistic. The sale price of a condominium unit in the
District Lofts building across the street was estimated to include a benefit of
$24,482 attributed to its view onto the 401 Richmond rooftop garden.
ƒ
Since the construction of the rooftop garden, the 401 Richmond property has
enjoyed an estimated $83,126 in free publicity. The estimate appears to be
realistic.
ƒ
The stormwater management benefit is estimated to range between $1,217
and $38,736. Given that the building is located in an extremely dense urban
environment with very high land values, low cost stormwater management
solutions (which are land intensive) are not an option. For this reason, the
value of the benefit is likely to be at the upper end of the range in this case.
ƒ
The air quality benefit is estimated to be worth between $43.79 and $71.01.
Given the prevalence of bushes and vines and the relatively small area of the
extensive portion of the roof, the value is likely to tend towards the upper
range.
ƒ
The GHG sequestration benefit is estimated to be worth between $2.41 and
$3.31. Given that the garden includes a mix of bushy plants, some small trees
and various small plants (i.e., sedum on the extensive portion), the value of
the benefit is likely to tend towards the middle of the range.
63
4.4 Case Stud
dy 4 – Roofftop Victory Gardens, Chicago
o, IL 4.4.1 Key Featu
ures location 6034 Nortth Broadwayy, Chicago, IL type of building supermarrket; former auto mechaanic shop numb
ber of storeyys 1 type of green roo
of intensive
roof cconstruction
n retrofit comp
pletion date 2006 developer Urban Habitat Chicag o and True N
Nature Food
ds desiggner Dave Ham
mpton / Echoo Studio 2
vegettative area 163.5 m (1,760 sq ft))* depth
h of growingg medium 1.3 cm to 10.2 cm (0.55” to 4”) type of vegetatio
on various he
erbs and veggetables accesssibility accessible
e to project vvolunteers o
only 2
* Inclludes 74.3 m (800 sq ft)
f planned Phase II exp
pansion.
6
64
4.4.2 Summaryy of Project The Rooftop
R
Victory Garden
n is hosted by
b True
Nature Foods, an
n organic fo
ood cooperaative and
neigh
hbourhood recycling ceentre in the Edgewaterr
district on the north side off Chicago. Th
he garden
takess its name frrom the factt that the saame site wass
used as a ‘victory garden’ during the World
W
Wars.
So-caalled victory
y gardens orr war gardeens were
plantted at privatte residencees in the US
S, the UK,
and Canada
C
duriing the wars to reduce pressure on
n
the public
p
food supply.
s
Urbaan Habitat Chicago (UHC), a local non-profit
n
group promoting sustainab
ble practicess in urban
nitiated the project in 2005.
2
UHC
envirronments, in
was awarded
a
a $5,000
$
gran
nt from the City
C of
Chicaago Green Roof
R
Grants Program to
owards the
realizzation of the project. No other finaancing was p
provided; th
he project w
was
developed throu
ugh volunteer labour an
nd pro-bonoo architectu
ural consultations. After
den was imp
plemented in
n
over a year of reesearch and design, thee first phase of the gard
ber 2006. The
T first harvest occurred the follo wing summ
mer.
Octob
The garden’s
g
peak growing season is between Mayy and August. Species ggrown havee
so farr included: amaranth, basil,
b
buckw
wheat, collarrd greens, eeggplant, greeen beans,
horseeradish, varrious tomato
oes, lavendeer, mushroooms, mustarrd greens, o
onions, bell
and chili
c
pepperrs, potatoes,, sage, snap peas, thyme, wheat, an
nd zucchini.. The speciees
are rotated depeending on th
he season. In addition, burdock, cleome, cloveer, cosmos,
dand
delions, marrigolds, and a variety off grasses ha ve been plaanted to help
p establish
the growing
g
med
dium and atttract benefficial insectss. The produ
uce grown d
during the
2007
7 and 2008 seasons
s
was mostly disstributed am
mong projecct volunteerrs and somee
was sold
s
at the store
s
below
w (UHC, 2008
8).
According to thee UHC, the Rooftop
R
Victtory Garden
ns have beco
ome the “po
oster child”
he City of Ch
hicago's Greeen Roof Graants Prograam. The projject has beeen the
for th
subjeect of news reports in local, nation
nal and even
n some interrnational m
media (UHC,
undaated).
6
65
66
4.4.3 Benefits Calculations benefit property value applicable ‐ view onto a green roof ‐ recreational rooftop garden ‐ productive rooftop garden marketing sound attenuation food production stormwater retention air quality GHG sequestration comment tested on residential property at 1214 W Norwood St. not recreational assumed to accrue to host and to neighbouring properties; tested on residential property at 1214 W Norwood St. insufficient data no source of significant overhead noise 4.4.4 Variables See Table 9 for a definition of the variables.
v = US$107,871
vv = US$433,856*
d = 11 m
h = 1 storeys
hv = 2 storeys*
a = 163.5 m2
g = 7 months
* Four-unit residential property at 1214 W Norwood St., directly behind the True
Nature Foods property (source: Cook County Assessor’s Office, 2009)
4.4.5 Calculations 4.4.5.1 propertyvalue
View onto a green roof: Whole building gain in property value Since the current property value presumably includes the benefit of a view onto a
green roof, we let:
vnx = neighbouring property value excluding the benefit ($)
67
v v = vnx + b
and
b = 0.045⋅
hv − h
⋅ vnx
hv
therefore
v v = vnx + (0.045⋅
= vnx + (0.045⋅
hv − h
⋅ vnx )
hv
(2)−(1)
⋅ vnx )
(2)
v v = 1.0225⋅ vnx
vv
1.0225
($433,856)
=
1.0225
= $424,309
vnx =
b = v v − vnx
= ($433,856)−($424,309)
= $9,546
Host property with productive rooftop garden Since the current property value includes the productive green roof benefit, we let:
vx = property value excluding the benefit ($)
68
v = vx + b
and
b = 0.07⋅ v x
therefore
v = v x + (0.07⋅ v x )
v = 1.07⋅ v x
v
1.07
($107,871)
=
1.07
= $100,814
vx =
b = 0.07($11,602,500)
= $7,057
Property neighbouring with a productive rooftop garden Since the current property value includes the productive green roof benefit, we let:
vnx = neighbouring property value excluding the benefit ($)
v = vnx + b
and
b = F ⋅ vnx
therefore
v = vnx + (F ⋅ vnx )
v = vnx +[(0.05)⋅ vnx ]
v = 1.05⋅ vnx
v
1.05
($433,856)
=
1.05
= $413,196
vnx =
b = 0.05($413,196)
= $20,660
69
4.4.5.2 foodproduction
Low scenario b = ($2/ m2 ⋅ month)⋅ g ⋅ a
=($2/ m2 ⋅ month)⋅(7months)⋅(163.5m2 )
= $2,289
High scenario b = ($20/ m2 ⋅ month)⋅ g ⋅ a
=($20/ m2 ⋅ month)⋅(7months)⋅(163.5m2 )
= $22,890
4.4.5.3 stormwaterretention
Low‐cost stormwater retention infrastructure scenario b = $1.44/m2 ⋅ a
= $1.44/m2 ⋅(163.5m2 )
= $235
High‐cost stormwater retention infrastructure scenario b = $45.82/ m2 ⋅ a
= $45.82/ m2 ⋅(163.5m2 )
= $7,491
4.4.5.4 airquality
Low scenario (100% short grass coverage) b = ($0.0074 / m2 ⋅ months) ⋅ g ⋅ a
= ($0.0074 / m2 ⋅ months) ⋅(7months) ⋅(163.5m2 )
= $8.47
70
High scenario (100% deciduous tree coverage) b = ($0.0120/m2 ⋅ months)⋅ g ⋅ a
= ($0.0120/m2 ⋅ months)⋅(7months)⋅(163.5m2 )
= $13.73
4.4.5.5 GHGsequestration
Low scenario (100% grass coverage) b =($28.46/ ha)⋅ a
=($28.46/ ha)⋅(0.01635ha)
= $0.47
High scenario (100% deciduous coverage) b = ($39.11/ ha)⋅ a
= ($39.11/ ha)⋅(0.01635ha)
= $0.64
4.4.6 Benefits Summary benefit property value (host) property value (neighbour) proximity to productive garden property value (neighbour) view onto green roof marketing food production stormwater retention air quality GHG sequestration type one time value $7,057
one time $20,660
one time $9,546
one time annual one time annual annual $2,289 – $22,890
$235 – $7,491
$8.47 – $13.73
$0.47 – $0.64
4.4.7 Observations ƒ The property value benefit of $7,057 that accrues to the True Nature Foods
store seems realistic. The residential building behind True Nature Foods, at
1214 W Norwood, was assumed to benefit from being close to what is more
or less a community garden, gaining as much as $20,660 from its proximity
to the garden. This assumption implies that the residents of 1214 W
Norwood are able to participate in the gardening activities at True Nature
Foods and they receive part of the garden’s yield. The 1214 W Norwood
building also has a view onto the garden, which affords a considerably
smaller benefit of $9,546. It should be noted that the garden is not designed
71
ƒ
ƒ
ƒ
ƒ
for visuall appeal and
d therefore it is questioonable whetther the view
w benefits
apply in this
t case.
The prod
duction food
d production
n value wass estimated to be betweeen $2,289
and $22,8
890. Given that
t
the garden producces many veegetables, in
ncluding
inexpensive staples but also som
me high valu
ue-added sp
pecies such as herbs
and lettuces, the valu
ue of the beenefit is like ly to be in the middle o
of the range.
The storm
mwater man
nagement benefit
b
is esttimated to rrange betweeen $235
and $7,49
91. Given th
hat the build
ding is locatted in a med
dium-densitty urban
area with
h moderate land valuess, high cost ((below grad
de) stormwaater
managem
ment solutio
ons are unlik
kely to be n ecessary. A
At the same ttime, being
an urban environmeent, some beelow grade sstormwaterr retention
infrastructure is likeely to be neeeded. For th
hese reasonss, the value of the
ng towards the higher
benefit iss likely to bee in the middle of the raange, tendin
end.
worth betweeen $8.47 an
nd $13.73.
The air quality benefit is estimaated to be w
Given thee prevalencee of leafy plants, the vaalue is likelyy to tend tow
wards the
upper ran
nge.
The GHG sequestratiion benefit is estimated
d to be wortth between $0.47 and
$0.64. Giv
ven that garrden includees mostly sm
mall plants,, the value o
of the benefiit
is likely to
t tend towaards the low
wer end of th
he range.
4.5 Case Stud
dy 5 – The Louisa, Po
ortland, OR
R 7
72
4.5.1 Key Features location type of building number of storeys type of green roof roof construction completion date developer designer vegetative area depth of growing medium type of vegetation accessibility 123 Northwest 12th Avenue, Portland, OR residential 18 semi‐intensive new construction 2005 Gerding Elden Development Walker Macy 584.9 m2 (6,296 sq ft) extensive; 749.8 m2 (8,071 sq ft) intensive 10.2 cm (4”) to 61.0 cm (24”) drought tolerant native species (grasses and bushes) accessible to tenants of The Louisa only 4.5.2 Summary of Project The Louisa is a residential high-rise apartment building with 242 apartments and
ground floor retail, situated in the historic Pearl District of downtown Portland. The
property was developed and is owned by Gerding Elden, a development firm
specializing in mixed-use, sustainable urban development. The Louisa is part of the
Brewery Blocks redevelopment project. The project, which covers five city blocks,
takes its name from the defunct brewery that once occupied the site.
The Louisa building is composed of a large podium at the base, which houses the
retails spaces, and a tower set at the back of the podium, which contains the bulk of
the apartments. The green roof is situated on top of the podium and can therefore
be viewed directly from at least half of the apartments in the tower. The green roof
features both extensive and intensive components. The larger (749.8 m2) portion of
the roof is an accessible recreational rooftop garden with intensive vegetation. The
garden is flanked on either side by non-accessible extensive green roofs (292.5 m2
each). These are two storeys higher than the garden as they sit on top of two-storey
townhouse units facing into the garden. Both the intensive and extensive portions
are planted with drought-tolerant native species, which can withstand Portland’s
relatively dry summers with minimal watering (Peck, 2008).
The Louisa was built to meet the US Green Building Council’s strict LEED criteria for
new buildings. Its intensive and extensive green roofs are among its many green
features, which have earned it a rating of LEED-Gold – the second highest
sustainability rating given by the Green Building Council. In the 2007, the Green
Roofs for Healthy Cities annual award for best intensive residential green roof
project was conferred upon the Louisa.
73
74
4.5.3 Benefits Calculations benefit property value ‐ recreational rooftop garden ‐ productive rooftop garden ‐ view onto a green roof marketing applicable sound attenuation food production comment no food produced from upper floors of the Louisa data unavailable no source of significant overhead noise no food produced stormwater retention air quality GHG sequestration 4.5.4 Variables v = US$56,924,000.00
vv = US$56,924,000.00
h = 2
hv = 18
a = 1,334.7 m2 (= 584.9 m2 + 749.8 m2)
g = 9 months
4.5.5 Calculations 4.5.5.1 propertyvalue
View onto a green roof: whole building gain in property value Since the current property value includes the view benefit, we let:
vx = property value excluding the view benefit ($)
75
vv = vx + b
and
b = 0.045⋅
hv − h
⋅ vx
hv
therefore
v v = v x + (0.045⋅
= v x + (0.045⋅
hv − h
⋅ vx )
hv
(18)−(2)
⋅ vx )
(18)
v v = 1.04⋅ v x
vv
1.04
($56,924,000)
=
1.04
= $54,734,615
vx =
b = vv − vx
= ($56,924,000)−($54,734,615)
= $2,189,385
Host property with recreational rooftop garden Since the current property value includes the property value benefit, we let:
vx = property value excluding the benefit ($)
76
v = vx + b
and
b = 0.11⋅ v x
therefore
v = v x + (0.11⋅ v x )
v = 1.11⋅ v x
v
vx =
1.11
(56,924,000)
=
1.11
= 51,282,882
b = 0.11(51,282,882)
= 5,641,117
4.5.5.2 stormwaterretention
Low‐cost stormwater retention infrastructure scenario b = $1.44/ m2 ⋅ a
= $1.44/ m2 ⋅(1,334.7m2 )
= $1,922
High‐cost stormwater retention infrastructure scenario b = $45.82/ m2 ⋅ a
= $45.82/ m2 ⋅(1,334.7m2 )
= $61,156
4.5.5.3 airquality
Low scenario (100% short grass coverage) b = ($0.0074 / m2 ⋅ months) ⋅ g ⋅ a
= ($0.0074 / m2 ⋅ months) ⋅(9months) ⋅(1,334.7m2 )
= $88.89
77
High scenario (100% deciduous tree coverage) b = ($0.0120/m2 ⋅ months)⋅ g ⋅ a
= ($0.0120/m2 ⋅ months)⋅(9months)⋅(1,334.7m2 )
= $144.15
4.5.5.4 GHGsequestration
Low scenario (100% grass coverage) b =($28.46/ ha)⋅ a
=($28.46/ ha)⋅(0.13347ha)
= $3.80
High scenario (100% deciduous coverage) b =($39.11/ ha)⋅ a
=($39.11/ ha)⋅(0.13347ha)
= $5.22
4.5.6 Benefits Summary benefit property value (view) type value one time $2,189,385
$5,641,117
property value (accessible recreational garden) one time stormwater retention air quality GHG sequestration one time annual annual $1,922 ‐ $61,156
$88.89 ‐ $144.15
$3.80 ‐ $5.22
4.5.7 Observations ƒ Two types of property value benefits can accrue to the Louisa property: a
benefit due to having an accessible recreational rooftop garden, worth
$9,487,333; and a benefit resulting from close to half the units in the Louisa
having a view onto the rooftop garden, worth $2,189,385. It is plausible to
argue that these two benefits are additive. If the rooftop were on top of the
building, affording no views from within the building itself, we would still
estimate a property value of benefit of $9,487,333. The two benefits added
together would thus yield a total property value benefit of $11,676,718.
ƒ The stormwater management benefit is estimated to range between $1,922
and $61,156. Given that the building is located in a very dense urban
environment with very high land values, low cost stormwater management
78
ƒ
ƒ
solutions (which are land intensive) are not an option. For this reason, the
value of the benefit is likely to be at the upper end of the range in this case.
The air quality benefit is estimated to be worth between $88.89 and $144.15.
Given that the roof is semi-extensive, with both mixed grassy and leafy
vegetation, the value of the benefit is likely to tend towards the middle of the
range.
The GHG sequestration benefit is estimated to be worth between $3.80 and
$5.22. Given that the roof is semi-extensive, with both mixed grassy and leafy
vegetation, the value of the benefit is likely to lay in the middle of the range.
79
5 Conclusions This report has provided evidence that soft benefits produce economic advantages
for individual property owners, municipalities, and society at large. Despite the fact
that the benefits depend on the local context, we have provided heuristic methods to
estimate the economic value associated with seven soft-benefits. These are methods
that can be used by property owners, developers, architects, municipal officials, and
other stakeholders with information that is often readily-at-hand. The reader should
keep in mind the assumptions that had to be made in order to arrive at these quick
calculation methods. Some of these assumptions, along with the beneficiaries,
benefiting period, and a short statement of the valuation method appear in Table 11.
Table 11 ‐ Summary of Soft Benefit Valuations Section
Benefit Category
3.1
Property Value
Beneficiaries
Assumptions
Type Valuation
Error! Reference source not found. view onto a green roof property owner* and/or neighbours independent of area one‐time
up to 4.5% property value (portion above green roof)
3.1.1 property owner
independent of area
one‐time
recreational garden
up to 11% property value
3.1.3 productive garden
property owner
occupant access, independent of area
one‐time
up to 7% property value
neighbours (adjacent)
public access, independent of area
one‐time
up to 7% property value
neighbours (150 m)
public access, independent of area
one‐time
up to 5% property value
neighbours (300 m)
public access, independent of area
one‐time
up to 2% property value
3.2
Marketing
property owner
comparable to free publicity
one‐time
see Table 3
3.3
Food production
tenants, property owner
excludes labour and material costs
ongoing
$2‐$20/m2 per growing month
3.4
Sound attenuation
property owner
affects top floor only, each floor is worth an equal portion of the total property value, independent of area but assume extensive coverage
one‐time
1.6% to 4.3% property value of top floor
3.5
Stormwater retention
developer, municipality
42.7L/m2 retention capacity
one‐time
$1.44/m2 to 2
$45.82/m
80
3.6
Air quality
municipality, region
ongoing
$521/ha to $839/ha per year
3.7
GHG sequestration
municipality, region, planet
ongoing
$28/ha to $39/ha per year
*If the green roof can be seen from at least part of the host property
The case studies presented in this report show that the proposed valuation
methodologies can be applied in real-life situations without requiring large (or
difficult to obtain) data inputs. In general, the valuations returned by applying the
methodologies seem to be of a reasonable magnitude. The observations presented
at the end of each case study should help the reader interpret the results and judge
how best to apply the methodologies in their own context.
Among the one-time benefits proposed here, the property value benefits are by far
the most significant. Properties with accessible green roofs are subject to a 11%
property value premium, while those with rooftop food gardens gain 7% in property
value. Neighbours of both types of green roofs also stand to benefit significantly
from their presence. Buildings with views onto a green roof could gain up to 4.5% of
property value (depending on how many floors have a view of the greenroof), while
those adjacent to rooftop food gardens could gain from 2% to 7% (depending on
distance from the building with the rooftop garden). It should be noted that the sum
of the all the property value gains accruing to neighbouring properties could be
considerably larger than the value of the benefit accruing to the host property.
Sound attenuation offers one-time benefits on a similar order of magnitude, ranging
from a 1.6% to a 4.3% property value premium on the value of the top floor.
However, this benefit only arises if there is a significant source of overhead noise,
such as air traffic or an elevated train nearby. As for the marketing benefit, also a
one-time benefit, the experience of the 401 Richmond building in Toronto (Case
Study 3, Section 4.3) suggests that it is relatively small – 0.6% of property value in
this case.
The value of the stormwater management benefit varies considerably when viewed
as a fraction of property value. In the 401 Richmond case, for example, it is
estimated to be worth between 0.01% and 0.28% of property value, whereas in the
case of the True Nature Foods Victory Garden, it is estimated to be worth 0.2% to
6.9% of the property value. This benefit is not tied to property value but rather to
the area of the green roof; True Nature Foods has low property value but a relatively
large roof and the stormwater benefit is therefore much larger relative to property
value.
Where ongoing benefits are concerned, the food production benefit is much more
valuable than the air quality and GHG sequestering benefits, according to our
methods of estimation. We propose that the value of the food produced on a rooftop
garden is worth $2 to $20 per square metre per month in the growing season. As
most of the North American population lives in places where the growing season is
81
at least 6 months long, the benefit is therefore worth at the very least $12/m2 of
rooftop growing area per year. In places with a year-round growing season, such as
in the southern coastal states, the benefit could be worth up to $240/m2 per year. In
contrast, the air quality benefit is worth between $0.0521/m2 to $0.0839/m2 per
year and the GHG sequestration benefit is worth $0.0028/m2 to $0.0039/m2 per
year.
The difference between food production and air quality/GHG benefits is well
illustrated by the two case studies that feature rooftop food production (Case
Studies 2 and 4). In Case Study 2, on the Fairmont Waterfront Hotel herb garden,
food production is estimated to be worth $3,121 to $31,210 per year, while air
quality improvement is worth $11.54-$18.73 per year and GHG sequestration is
worth a mere $0.56-$0.76 per year. In Case Study 4, on the True Nature Foods
Rooftop Victory Garden, food production is estimated to be worth $2,289 to $22,890
per year, while air quality improvement is worth $8.47-$13.73 per year and GHG
sequestration is worth a mere $0.47-$0.64 per year.
Given how small the air quality and GHG sequestration benefits are, it is almost
meaningless to include them in an assessment of the benefit values for individual
green roofs. Both of these benefits would be more meaningful if calculated for
numerous green roofs covering a substantial portion of a neighbourhood or city. For
example, as reported above, Bating et al (2005) calculated that if all flat rooftops
across the City of Toronto were extensively greened, the annual cost savings
attributable to reduction in air pollution would amount to US$1,970,000
(C$2,700,000 in 2008).
Readers are reminded that the methodologies offered here are heuristic in nature;
they are rough estimations based on a number of assumptions that are reasonable
in most cases but may not be applicable in specific contexts. Changes in the
assumptions will of course lead to a different evaluation of benefits. Also, the report
provides calculation methods for a range of greenroof conditions. These are meant
to serve as benchmarks only and of course do not cover all potential situations. The
user is asked to use their own best judgment as to whether and how the
assumptions made and range of conditions covered in this report can be usefully
applied or adapted to their own unique situation.
It is also important to keep in mind when using the calculation methodologies
presented in this report that we did not account for any of the costs involved in
producing the benefits. Most importantly, we did not account for the extra costs
involved in creating a green roof compared to a conventional roof. Nor did we
include the higher property taxes that might accrue to buildings whose property
values have been increased due to the presence of a green roof. Finally, we did not
account for direct inputs such as the cost of materials and labour that go into food
production.
82
As already noted, the goal of this report was to allow users to make rough
calculations of benefits without undertaking a major research effort. For the most
part, this has been achieved: the equations require data that is usually readily
available such as property value, building height, roof area, and so on. The sole
exception is the marketing benefit, which requires detailed information on publicity
gained due to the green roof. Our experience with the case studies suggests that
most green roof property owners do not have precise information on media
coverage, if they track it at all. Future research might address this by tracking media
coverage across many green roof projects and generating a more generic formula
for estimating the value of the marketing benefit.
To our knowledge, this is the first attempt in the growing literature on green roofs
to offer a means for calculating the value of a range of soft benefits associated with
the use of the technology. Clearly, however, it is not the last word. Future research
may not only allow us to refine the approaches offered here but to expand the range
of soft benefits covered to include, for example, habitat creation and community
building. If this report has helped put us on this path, then it has served its purpose.
83
Interviewees Michelle Bates-Benetua
Lettuce Link Program Manager
Solid Ground
michelleb@solid-ground.org
206-694-6754
Martine Desbois
Coordinator of Sustainability Initiatives
Dockside Green
mdesbois@docksidegreen.com
250-360-1100 x 227
Neil Jamieson
Executive Sous Chef
Fairmont Waterfront
neil.jamieson@fairmont.com
604-691-1991 x1611
Emily Lake
Director of Urban Agriculture
Urban Habitat Chicago
emilyhlake@gmail.com
Robert Lotz
Advertising Sales Representative
103.9 PROUD-FM
robertlotz@hotmail.com
416-948-7944
Erin MacKeen
Communications Director
Urbanspace
erin@urbanspace.org
416-595-5900 x 25
Rich McDonald
P-Patch Program Manager
Department of Neighborhoods
City of Seattle
84
rich.macdonald@seattle.gov
206-386-0088
Sky Seeley
Sales Coordinator
Dockside Green
sky@docksidegreen.ca
250-380-7278
85
Bibliography Akbari, H. & Konopacki, S. (2003). Streamlinedenergy‐savingscalculationsforheat‐
islandreductionstrategies. Lawrence Berkeley National Laboratory: Berkeley, CA.
LBNL Paper #47307.
Banting, D., Doshi, H., Li, J., Missios, P., Au, A., Currie, B.A., & Verrati, M. (2005).
ReportontheEnvironmentalBenefitsandCostsofGreenRoofTechnologyfortheCity
ofToronto. Report prepared for the City of Toronto and Ontario Centres of
Excellence – Earth and Environmental Technologies (OCE-ETech)
(http://www.toronto.ca/greenroofs/pdf/fullreport103105.pdf).
Barrs, R. (2002). SoutheastFalseCreekUrbanAgricultureStrategy. Holland-Barrs
Planning Group in Association with Lees + Associates.
Bateman, I., Day, B., Lake, I., & Lovett, A. (2000). TheEffectofRoadTrafficon
ResidentialPropertyValues:ALiteratureReviewandHedonicPricingStudy.
Edinburgh: Scottish Office, Development Department.
Bay Localize (2008). BayLocalizeWebGallery–TrueNatureFoodsRooftopVictory
Garden. Webpage
(http://www.baylocalize.org/webgallery/thumbnails.php?album=48&page=2).
Brown, K. (2002). UrbanAgricultureandCommunityFoodSecurityintheUnited
States:FarmingfromtheCityCentertotheUrbanFringe. Community Food Security
Coalition.
Canada Mortgage and Housing Corporation (CMHC) (2003). FairmontWaterfront
HotelGreenRoofHerbGardenCaseStudy,Vancouver,BritishColumbia. From the
CMHC Innovative Buildings series (http://www.cmhcschl.gc.ca/en/inpr/bude/himu/inbu/upload/Fairmont-Waterfront-Hotel.pdf).
Canadian Automobile Association (2008). DrivingCosts,2008Edition. Retrieved
from: http://www.caa.ca/documents/DrivingCostsBrochure-2008-eng-web.pdf.
Carter, T. & Keeler, A. (2008). Life-cycle cost–benefit analysis of extensive vegetated
roof systems. JournalofEnvironmentalManagement 87, 350-363.
Champ, P., Boyle, K., & Brown, T. (2003). APrimeronNon‐marketValuation.
Dordrecht, Netherlands: Kluwer Academic Publishers.
City of Victoria (2005). DocksideDevelopment,MasterDevelopmentAgreement.
Retrieved from: http://www.victoria.ca/cityhall/currentprojects_dockside.shtml.
86
City of Waterloo (2005). GreenRoofFeasibilityStudyandCityWideImplementation
Plan. Public document (http://www.city.waterloo.on.ca/Portals/57ad7180-c5e749f5-b282c6475cdb7ee7/LIBRARY_Plans_documents/GRReport2005Complete.pdf).
Clark, C. (2005). Optimization of Green Roofs for Air Pollution Mitigation. In
ProceedingsfromGreeningRooftopsforSustainableCommunitiesConference2005,
WashingtonDC.
Clark, C., Adrieans, P. & Talbot, F.B. (2008). Green Roof Valuation: A probabilistic
economic analysis of environmental benefits. EnvironmentalScienceTechnology
42(6), 2155-2161 (http://pubs.acs.org/cgibin/abstract.cgi/esthag/2008/42/i06/abs/es0706652.html).
Connelly, M. & Hodgson, M. (2008). Sound Transmission Loss of Extensive Green
Roofs - Field Test Results. AcousticsWeekinCanada,October6‐8,2008. Vancouver,
BC: Canadian Acoustical Association.
Costanza, R., d'Arge, R., de Groot, R., Farber, S., Grasso, M., Hannon, B., et al. (1998).
The value of the world’s ecosystem services and natural capital. Ecological
Economics, 25(1), 3-15.
Crompton, J. (2005). The Impact of Parks on Property Values: Empirical Evidence
from the Past two Decades in the United States. ManagingLeisure 10(4), 203-21.
Cunnigham, N. (2001). RethinkingtheUrbanEpidermis:astudyoftheviabilityof
extensivegreenroofsystemsintheManitobacapitalwithanemphasisonregional
casestudiesandstormwatermanagement. Master’s thesis dissertation, Department
of Landscape Architecture, University of Manitoba, Winnipeg, Manitoba.
Curran, D. (2001). EconomicBenefitsofNaturalGreenSpaceProtection. The POLIS
Project on Ecological Governance and Smart Growth BC.
Currie, B.A. (2005). AirPollutionMitigationwithGreenRoofsUsingtheUFOREModel.
Unpublished Master’s Thesis, Ryerson University, Toronto.
Currie, B.A. & Bass, B. (2008). Estimates of air pollution mitigation with green plants
and green roofs using the UFORE model. UrbanEcosystems11, 409-422.
David Suzuki Foundation (2008). Ontario’sWealth,Canada’sFuture:Appreciating
theValueoftheGreenbelt’sEco‐Services. Public document
(http://www.davidsuzuki.org/files/Conservation/DSF-Greenbelt-web.pdf).
De Groot, R. S. (1992). Functions of nature: Evaluation of nature in environmental
planning. In Groningen, Netherlands: Wolters-Noordhoff.
87
Department for Environment, Food and Rural Affairs (DEFRA). (2007). An
IntroductoryGuidetoValuingEcosystemServices.
Economic and Planning Systems, Inc. (2000). QuantifyingourQualityofLife:An
EconomicAnalysisoftheEastBay'sUniqueEnvironment.
Eisenberg, Olivieri, & Associates, Inc. (EOA) (2007). DevelopmentsProtectingWater
Quality:AGuidebookofSiteDesignExamples. Report produced for the Santa Clara
Valley Urban Runoff Pollution Prevention Program (http://www.scvurpppw2k.com/pdfs/0607/SC_Site_Design_Manual_Final_0207.pdf).
Environmental Protection Agency (EPA) (1998). RegulatoryImpactAnalysisforthe
NOx SIPCall,FIP,andSection126Petitions. Report EPA-452/R-98–003A.
Environmental Protection Agency (EPA) (1999). Preliminarydatasummaryofurban
stormwaterbestmanagementpractices. Report EPA 821-R-99-012.
Edwards, K. (2007). DoParksMakeCents?:AnAnalysisoftheEconomicValueof
ParksinSanFrancisco. UC Berkeley, Richard and Rhoda School of Public Policy.
Fankhauser, S. (1994). The social costs of greenhouse gas emissions: an expected
value approach. TheEnergyJournal 15(2), 157–184.
Goodman Williams Group and URS Corporation. (2005). MillenniumPark:Economic
ImpactStudy.
Grover, R. (2006). Are DVRs killing network TV? BusinessWeek, May 11
(http://www.businessweek.com/bwdaily/dnflash/may2006/nf20060511_7450_db
011.htm?campaign_id=rss_daily).
Hendricks, J. (2005). Zeroing on the Decision-Makers: Knowing the Potential Green
Roof Client. GreeningRooftopforSustainableCommunities. Washington, DC.
Hidano, N. (2002). TheEconomicValuationoftheEnvironmentandPublicPolicy.
Cheltenham, UK: Edward Elgar Publishing.
Intergovernmental Panel on Climate Change (IPCC) (2007). Summary for
Policymakers. In ClimateChange2007:Impacts,AdaptationandVulnerability.
ContributionofWorkingGroupIItotheFourthAssessmentReportofthe
IntergovernmentalPanelonClimateChange. M.L Parry, O.F. Canziani, J.P. Palutikof,
P.J. van der Linden and C.E. Hanson, Eds. Cambridge University Press, Cambridge,
UK, 7-22.
Jamieson, N. (2008). RoofTopHerbGarden. Media factsheet prepared by the
Executive Sous Chef of the Fairmont Waterfront Hotel restaurant.
88
King, A., & Lenox, M. (2001). Does It Really Pay to Be Green?: An Empirical Study of
Firm Environmental and Financial Performance. JournalofIndustrialEcology, 5(1),
105-116.
Kowal, C. (2008). Measuring Urban Green. TheNewPlanner, Winter
(http://www.planning.org/thenewplanner/2008/win/measuringurbangreen.htm)
Miller, A. R. (2001). Valuingopenspace:Landeconomicsandneighborhoodparks.
Cambridge, MA, MIT Center for Real Estate (http://hdl.handle.net/1721.1/8754).
Morikawa, H., Takahasi, M., and Kawamura, Y. (1998). More than a 600-fold
variation in nitrogen dioxide assimilation among 217 plant taxa. Plant,Cell&
Environment 21, 180–190.
Navrud, S. (2002). TheState‐Of‐The‐ArtonEconomicValuationofNoise. Final Report
to European Commission DG Environment.
Nowak, D., & Crane, D. (1998). The Urban Forest Effects (UFORE) model: quantifying
urban forest structure and functions. IntegratedToolsProceedings, Idaho, 16-20
(http://www.nrs.fs.fed.us/pubs/gtr/gtr_nc212/gtr_nc212_714.pdf).
Nowak, D., & Crane, D. (2002). Carbon storage and sequestration by urban trees in
the United States. EnvironmentalPollution116, 381-389.
Ontario Medical Association (OMA) (2000). TheIllnessCostsofAirPollutionin
Ontario. Public report (http://www.oma.org/phealth/icap.htm).
Patel, I. (1991). Gardening's Socioeconomic Impacts: Community Gardening in an
Urban Setting. JournalofExtension ,29 (4), 7-9.
Peck, S. (2008). AwardWinningGreenRoofDesigns. Toronto: Green Roofs for
Healthy Cities. Peck, S., & Callaghan, C. (1999). GreenbacksFromGreenRoofs:ForgingaNew
IndustryInCanada. Peck and Associates.
Reed, J., Frazão, E., Itskowitz, R. (2004). HowmuchdoAmericansPayforFruitand
Vegetables?. United Sates Department of Agriculture, Economic Research Service.
September, A., & Peck, S. InnovativeBuildings:FairmontWaterfrontHotel. Canada
Mortgage and Housing Corporation.
South Coast Air Quality Management District (SCAQMD) (2007). AnnualRECLAIM
AuditReportforthe2005ComplianceYear. Public report
(http://www.aqmd.gov/hb/2007/March/070334a.html#_ftn1).
Statistics Canada (2007). Householdsize,byprovinceandterritory(2006Census).
Web page (http://www40.statcan.gc.ca/l01/cst01/famil53b-eng.htm).
89
Trust for Public Land (2008 a). HowMuchValueDoestheCityofPhiladelphiaReceive
fromitsParkandRecreationSystem? Report for the Philadelphia Parks Alliance.
Trust for Public Land (2008 b). QuantifyingtheGreenhouseGasBenefitsofUrban
Parks. August 2008 White Paper prepared by IFC International.
Urban Habitat Chicago (2008). Rooftop‐integratedfoodproductionFAQ. Webpage
(http://www.urbanhabitatchicago.org/blog/rooftopintegrated-food-productionfaq/).
Urban Habitat Chicago (undated). TrueNatureFoods. Webpage
(http://www.urbanhabitatchicago.org/projects/true-nature-foods/).
Urbanspace Property Group (2007a). IntensiveRoofGarden. Poster prepared for
Doors Open Toronto 2007
(http://www.401richmond.net/gardens/401%20Roof%20Garden%20Posters.pdf).
Urbanspace Property Group (2007b). ExtensiveRoofGarden. Poster prepared for
Doors Open Toronto 2007
(http://www.401richmond.net/gardens/401%20Roof%20Garden%20Posters.pdf).
Urbanspace Property Group (2008). 401Richmond:Building. Webpage
(http://www.401richmond.net/building/).
US Census Bureau (2006). 2006AmericanCommunitySurveyDataProfileHighlights.
Web page
(http://factfinder.census.gov/servlet/ACSSAFFFacts?_event=&geo_id=01000US&_g
eoContext=01000US&_street=&_county=&_cityTown=&_state=&_zip=&_lang=en&_s
se=on&ActiveGeoDiv=&_useEV=&pctxt=fph&pgsl=010&_submenuId=factsheet_1&d
s_name=DEC_2000_SAFF&_ci_nbr=null&qr_name=null&reg=&_keyword=&_industry
=).
Voicu, I. & Been, V. (2008). The Effect of Community Gardens on Neighboring
Property Values. RealEstateEconomics36(2), 281-243.
Wachter, S. (2004). TheDeterminantsofNeighborhoodTransformationsin
Philadelphia‐IdentificationandAnalysis:TheNewKensingtonPilotStudy. University
of Pennsylvania, The Wharton School.
Yang, J., Yu, Q., & Gong, P. (2008). Quantifying air pollution removal by green roofs in
Chicago. AtmosphericEnvironment 42, 7266-7273.
90