European Airport Greenroofs - a Potential Model

By Linda S. Velazquez, ASLA Associate, LEED AP Publisher & Design Consultant
with contributions by Benjamin Taube, City of Atlanta Environmental Manager
Airports occupy and consume huge areas of land mass, destroying ecosystems and
creating massive urban heat islands of impermeable, hot surfaces. For example, the area
of roofs and pavement at the Atlanta Hartsfield-Jackson International Airport (ATL) is
estimated at over 70,500,000 square feet, or 1,619 acres! When compared to surrounding
undeveloped areas, ATL infrared imagery, provided by NASA, clearly shows up to over
55°F thermal variations between the terminal, concourses, runways, parking decks and
lots, cargo and other airport support buildings. The resulting loss of natural greenspace
greatly impacts stormwater management, loss of habitat and biodiversity, creates noise,
air and water pollution, and on a large scale, contributes to global warming.
In addition, we know how the numerous ecological advantages of extensive greenroofs
could help mitigate each and every one of these environmental problems. Yet airports, as
a unique development type, also offer their own particular set of construction design
prerequisites and issues that are not applicable to a typical urban environment – in
particular, security and safety concerns.
Specifically, stormwater infrastructure engineering must immediately provide fast and
efficient drainage to all paved surfaces. And the recreated natural areas of runways and
surrounding fields are designed to avoid attraction of birds, which many times get drawn
into jet engines creating a potentially hazardous and life threatening situation.
Even given greenroofs’ ability to reduce stormwater infrastructure concerns, to date
airport authorities outside of Europe have been hesitant to consider vegetated roofs
mainly for fear of attracting birds. However, many airports in Europe have successfully
constructed greenroofs atop parking garages, hangers, and even terminal buildings,
without increasing their yearly number of “bird strikes.” Bird and wildlife hazard
statistics and accompanying industry support will be identified. This paper will attempt
to examine the impacts of using a greenroof within airports as well as address some of
the potential barriers to greenroofs, in particular the real danger of attracting birds.
To make the case for the implementation of airport greenroofs worldwide, greenroofed
buildings will be reviewed at the following international airports, offering insight as to
local motivating factors or market drivers; the resulting ecological, aesthetic and
economic benefits; and their specific design considerations including appropriate
system and plant types, and other elements necessary for a safe yet green environment:
Schiphol International Airport, Amsterdam, the Netherlands (AMS);
Frankfurt International Airport, Frankfurt, Germany (FRA);
Kloten International Airport, Zürich, Switzerland (ZRH)
Bird and wildlife management techniques and design considerations will be discussed,
along with “Lessons Learned” from our successful European airport greenroof
counterparts. Finally, using the Atlanta Hartsfield-Jackson International Airport - “the
World’s Busiest Airport” – as an example, we will present a design scenario of how
Atlanta’s largest urban heat island could be significantly mitigated by incorporating
greenroofs. We aim to help further airport greenroof interest by encouraging continued
research into these international examples of sustainable design and development.
Air transportation is an international growth industry and forecasts indicate that air traffic
volumes will continue to grow, even after the massive decline in 2001 following the 9/11 terrorist
attacks, and “Thousands of airports will need to be expanded, or built, to handle the Federal
Aviation Administration's projected 45% increase in flights by 2020.” According to the U.S.
Environmental Protection Agency and the General Accounting Office, this tremendous growth
will undoubtedly contribute to the existing pollution as medical studies reveal pollutants from jets
can cause heart failure or respiratory disease. On a large scale, sealed airport surfaces
contribute to global warming and cause crop damage, acid rain and reduced visibility1.
Airports across the world occupy and consume huge areas of land mass, destroying
ecosystems and creating massive urban heat islands of impermeable, hot surfaces with their
immense amount of concrete and asphalt. By incorporating greenroofs within these vast airport
facilities, it is extremely probable to offset the temperature increases caused by the amount of
impervious surface.
The Current Situation at ATL
Atlanta has the dubious distinction of claiming our airport as “The World’s Busiest Airport.”
Aviation General Manager Benjamin R. De Costa states that as the Metro Atlanta and the
southeast continue to grow both in terms of population and economic development, so does
Atlanta Hartsfield-Jackson International Airport (ATL). Like many high traffic airports worldwide
planning for future traffic demands, ATL must modernize and expand its current airport. The City
of Atlanta and the airlines at Hartsfield-Jackson have authorized the Airport to spend an
impressive $5.4 billion towards a 10-year development program. Currently, the ATL passenger
terminal complex measures 130 acres (52.6 hectares), or 5.7 million square feet2. Take into
consideration that the total area of roofs and pavement at ATL is estimated at over 70,500,000
square feet (65,496,643 m2), or 1,619 acres3.
NASA has been conducting a land use analysis study of Atlanta through its Project ATLANTA
(ATlanta Land use ANalysis: Temperature and Air quality) since 1996. Studies show that the
temperature in downtown Atlanta is often 10° F warmer than the surrounding outlying areas and
the added heat also contributes to Atlanta’s air quality problem as the 10-degree rise in
temperature doubles the amount of ozone that is produced4. According to NASA Senior
Research Scientist Dr. Dale A. Quattrochi, Atlanta's urban heat island is also creating its own
weather5. Situated just 10 miles south of downtown Atlanta, the massive amount of impervious
cover at Atlanta Hartsfield-Jackson International Airport adds to the huge heat island and
contributes to the area’s rising temperatures.
May 1997 color satellite photo of the
greater Atlanta area. The Chattahoochee
River and green areas are clearly
noticeable among the developed areas.
Thermal infrared photo of the greater
Atlanta area including the airport, seen in
red, on the lower right side.
The study has also measured and modeled the rapid growth of the Atlanta, Georgia
metropolitan areas since the early 1970’s and analyzed the impact on the region’s climate and
air quality. The NASA chart below shows the effects of urbanization and how land use affects
the magnitude of the heat.
When compared to surrounding undeveloped areas, the ATL infrared imagery shown below
clearly shows up to over 55°F of thermal variation between the terminal, concourses, runways,
parking decks and lots, cargo and other airport support buildings. The absence of natural
greenspace here greatly impacts stormwater management, loss of habitat and biodiversity,
creates noise, air and water pollution, and on a large scale, contributes to global warming.
May 1997 infrared imagery of ATL terminal, concourses, runways, parking and cargo areas.
Notice how the highest temperatures, shown in red, are the roof surfaces.
NASA research recommends planting or preserving more trees and greenspace and using lightcolored building materials that reflect solar energy to improve Atlanta's air6. And we know how
the numerous ecological advantages of extensive greenroofs could help mitigate other
environmental problems such as reducing noise volumes and providing habitat for small
Yet airports, as a unique development type, also offer their own particular set of construction
design prerequisites and issues that are not applicable to a typical urban environment – in
particular, security and safety concerns. One issue is the stormwater infrastructure engineering
which must immediately provide fast and efficient drainage to all paved surfaces.
Atlanta airport stormwater facts indicate that two main drainage basins handle most of the
detention/drainage within the airport infrastructure and prior to the 5th runway; the stormwater
detention on the SE side of the airport is supported by about 75% of all runoff from the airport.
South of the 5th runway a large detention structure is being installed and under the concourses,
ramps, and south cargo are holding systems to catch the first flush for pollutant removal7.
According to a recent edition of Grading and Excavating magazine, the newer airport facility
features four separate glycol retention/detention systems, each using 180 ft. of 48-in.- and 15in.-diameter pipe buried 25 ft. deep. The pipe serves as a containment system for stormwater
and deicing-solution runoff from the deicing pads. Beneath each deicing area is a
retention/detention system to capture deicing fluid and/or stormwater runoff. Hartsfield's system
is four 100- x 100-ft. holes containing three rows of Advanced Drainage System (ADS)
polyethylene (PE) pipe buried 22-25 ft. deep. The pipe serves as a fluid-holding pen, slowing
dispersal to the allowable outflow rate8.
This airport example is representative of aviation facilities worldwide and identifies some of the
developmental impacts on the land, illustrating the complex, strategic engineering necessary for
the quick and safe removal of airport stormwater volumes. Thousands of lives are at stake daily
on these impermeable airport surfaces of runways, taxiways, and shoulder areas. Yet
impermeable airport roof surfaces also cover a large percentage of total paved surfaces and
greenroofs offer an attractive opportunity to help alleviate the two greatest environmental
concerns of stormwater and heat islands while possibly providing other ecological advantages.
Wildlife and Airport Specific Design Considerations
An airport environment creates its own flight safety design challenges, necessitating specialized
spatial planning measures to consider both aviation and nature. Most public-use airports have
large tracts of open, unimproved land that are desirable for added margins of safety and noise
mitigation, but they often attract hazardous wildlife. The recreated natural areas of runways and
surrounding fields are designed to avoid attraction of birds, which many times get drawn into jet
engines creating a potentially hazardous and life threatening situation. Correct siting separation
criteria of aircraft movement areas, approach or departure airspace regulations, and controlling
land uses are measures used to discourage wildlife from interfering at airports.
Recognizing existing wildlife attractants, as well as mitigating the creation of new wildlife
attractants on or near the airport will help to reduce the risk of wildlife strikes, says the Federal
Aviation Administration (FAA)9. The wildlife species and the size of the populations attracted to
the airport environment are highly variable and may depend on several factors, including landuse practices on or near the airport. It is important to identify those land use practices in the
airport area that attract hazardous wildlife as large flocks near or above airfields are not simply
Bird Management Measures
Birds use airfields as a biotope for habitat, nesting and finding food and different species will
dictate different habitat preferences. In the medium and in the long term bird strikes on airfields
may only be minimized by identifying the ecological conditions that attract birds to an airfield
and then using habitat deterrence methods to make the airfield less attractive for species
relevant to flight safety10.
For example, U.S. Biologist Patrick Smith says grasses cut too low will attract flocks of birds or
geese. Grasses that grow too high will bring rodents, which in turn attract raptors11. Birds prevail
as do other living creatures by surviving through adaptation and specialization, and eventually
learn to live among humans and our built environments. For additional information on habitat
modification or other procedures for controlling hazardous wildlife at airports, see FAA's Wildlife
Hazardous Management at Airports12 and the Transport Canada Control Procedures Manual
Habitat Modification13.
Common Methods of Chasing Birds Away
This management can be as diverse as habitat manipulation to the use of predators to repelling
wildlife to lethal control of wildlife. Gunshots, blaring horns, crackers fired off with gas canisters,
hand-held laser devices, noisemakers, natural predators such as sheepdogs, border collies and
even falcons have all been employed in addition to bird warning systems like the “Bird
Avoidance Model (BAM), the U.S. Air Force's primary bird strike risk assessment tool. BAM is
an historical archive of bird information, taking data from more than 10,000 locations over the
past 30 years, for over 50 different bird species14.
Even given greenroofs’ ability to reduce stormwater infrastructure and other concerns, to date
airport authorities outside of Europe have been hesitant to consider vegetated roofs mainly for
fear of attracting birds. However, many airports in Europe have successfully constructed
greenroofs atop parking garages, hangers, and even terminal buildings, without increasing their
yearly number of “bird strikes.” So why shouldn’t we consider incorporating greenroofs on
airport area structures?
Some Bird Strike Statistics:
Over 195 people have been killed world-wide as a result of bird strikes since 1988.
Every year, over 1 billion dollars is wasted and lives are endangered worldwide when
birds and other wildlife collide with aircraft.
Wildlife strikes cost U.S. civil aviation over $500 million/year, 1990-200315.
Birds make up 97% of the reported strikes, mammals about 3% and reptiles less than
Over 4,300 bird strikes were reported by the U.S. Air Force in 2003.
Over 5,900 bird strikes were reported for U.S. civil aircraft in 2003.
An estimated 80% of bird strikes to U.S. civil aircraft go unreported17.
In Germany, an average of 1,500 bird strikes is reported annually for civil and military
Waterfowl (32%), gulls (28%), and raptors (17%) represented 77% of the reported bird
strikes causing damage to U.S. civil aircraft, 1990-2003.
A 12-lb Canada goose struck by a 150-mph aircraft at lift-off generates the force of a
1,000-lb weight dropped from a height of 10 feet.
At least 15,000 gulls were counted nesting on roofs in U.S. cities on the Great Lakes
during a survey in 1994.
About 90% of all bird strikes in the U.S. are by species federally protected under the
Migratory Bird Treaty Act19.
Bird strikes are a rather common event, but they rarely do much damage to an airplane, and
most strikes happen without anyone on board knowing about it. The most infamous encounter
happened in 1960 when an Eastern Airlines jet struck a flock of starlings and crashed into
Boston Harbor, killing 62 people20.
Bird Strike Industry Support
A large international industry support exists to facilitate the exchange of information, promote
the collection and analysis of accurate wildlife strike data, the development of new technologies
for reducing wildlife hazards, and professionalism in wildlife management programs on airports.
For example, Bird Strike Committee USA is a volunteer organization directed by a 9- to 12person steering committee consisting of 2-3 members each from the Federal Aviation
Administration (FAA), U.S. Department of Agriculture (USDA), Department of Defense, and
aviation industry21. Richard Dolbeer is the USDA/Wildlife Services National Coordinator, Airport
Safety and Assistance and his office manages the national database that records wildlife strikes
with aircraft each year and finds ways to keep the nation's air traffic safe from wildlife. The FAA
has an Airport Wildlife Hazard Mitigation website22. The German Bird Strike Committee (DAVVL
e.V.) is very comprehensive and publishes the scientific journal Bird and Aviation (ISSN 07214521), a technical periodical appearing usually twice annually since 1981, offering a wealth of
information on the subject in German and English23. And yearly regional and international
conferences meet to discuss trends.
Given all the concerns of flight safety and the bird population, conservation biologists still
estimate that by 2100 about 10% of all bird species probably will be extinct, killed off by habitat
loss, hunting and climate change24. With all this daunting information isn’t it still possible to
design airport buildings and areas with both human and wildlife safety and preservation in
mind? The answer is yes, of course.
European Airport Greenroofs
The notion of airport greenroofs may be new to many of us here in North America, but when I
started asking the Germans in particular about airport greenroofs, I was told that there are
thousands of square meters of greenroofs on airport buildings. Within Germany alone are
various greenroofs at Stuttgart, the new airport in Münich, in Bremen and the airport in
Düsseldorf. France has greenroofs at Charles de Gaulle in Paris, Paris’ Orly International
Airport and Bordeaux Airport. I have also seen an airport terminal greenroof in Milan, Italy and
more probably exist.
After security issues, noise abatement, air quality, and preservation of greenspace are the top
environmental concerns of area residents and airport management. Many greenroofing
companies have established themselves in Europe offering many system types and materials,
and manufacturers and providers. The following airport greenroof studies are based on
European aviation authorities and company representatives responding to our information
request, and are not intended to be exhaustive in scope.
Schiphol International Airport, Amsterdam, the Netherlands (AMS)
In 2002, the Schiphol International Airport management began defining their sustainable
development policy and six themes were identified. Of particular interest are “Safety” and
"Nature and Landscaping at Amsterdam Airport Schiphol" where they are planning to create
more awareness in the next few years for the flora and fauna located on the airport grounds as
well as for nature and landscaping activities. Schiphol ownership strives to ensure that the
airport landscape blends into the natural surroundings in the best way possible. For example,
they designed a system of canals and dense hedging to enclose the area around the new
runway. The policy prerequisite to avoid bird strikes includes deterring birds from coming to the
airport grounds by growing a longer species of grass and employing a team of specially trained
dogs to chase the birds away. Approximate number of bird strikes at AMS in 2003: 122 (KLM
figures not complete); 2002: 188; 2001: 122; 2000: 233; 1999: 20025.
The majority of roofs greened at Schiphol International Airport buildings have used Xero Flor
and ZinCo products. From our research and respondents we have estimated the
total airport area greenroofed at Schiphol International Airport and its surrounding Schipholrijk
neighborhood to be approximately 73,730 m2 or 793,623 square feet (sf). The Schiphol airport
itself contains three buildings with extensive greenroofs of 8500 m2 (91,493 sf), 3500 m2
(37,674 sf), and1330 m2 (14,316 sf). Schiphol also has two intensive greenroofs totalling 400
m2 (4,306 sf) bringing the airport total to 13,730 m2 or 147,789 sf. The Schipholrijk
neighbourhood has six buildings with intensive greenroofs measuring approximately 10,000 m2
(107,639 sf) each for a total of 60,000 m2 or 645,835 sf26.
Schiphol Plaza extensive greenroof - Constructed in 1994, the Schiphol Plaza Xero Flor
greenroof is situated over the main terminal and measures approximately 8,500 m2 (91,493 sf),
serving as a parking garage and train railway station. Designed by Benthem Crouwel NACO,
Mostert De Winter, Dutch licensees of the firm Strodhoff & Behrens Begruennungs GmbH of
Gross Ippener, Germany, installed the largest extensive greenroof at Schiphol using the Xero
Flor moss-sedum combination pre-vegetated mats Type XF 300c. The sedums and drought
resistant mosses are set in a mineral-based Xero Terr® substrate formula with a system
maximum saturated weight of 35 kg/m2 (7.168 lbs/sf); the substrate depth is just 40 mm
Schiphol Plaza; System: Xero Flor; Source:
Mostert De Winter website28.
Varying colors at Schiphol Plaza; Photo: Haven
Schiphol Real Estate and Sky-Master extensive greenroofs - Aart Veerman, President of the
International Green Roof Association and Commercial Director of Van der Tol b.v., estimated
the total area on the grounds of Schiphol-Airport greenroofed by Xeroflor with sedum mats to
include three roofs at 13,330 m2, to equal 143,483 sf. The other two large extensive roofs are
situated on the head office of "Schiphol Real Estate" and the “Sky-Master” building.
Mr. Veerman’s company, Van der Tol b.v., holds the maintenance contract on both. He states
that the maintenance of the sedums is really simple - the only extra measure is the filling of the
open space between the sedum mats to account for normal yearly shrinkage. Regarding bird
populations Aart says “So far as I can remember the facility-manager of Schiphol never spoke of
a bird problem in relation to the sedum-roofs.”
Schiphol Real Estate Building; System: Xero Flor; Source: Aart Veerman
Schiphol Vertrekhal Noord intensive greenroofs - Inside the departure and arrival buildings
are two small 400 m2 intensive patio roof gardens at Vertrekhal Noord that were built in 2001,
but they are not easy to visit because of strict security regulations. These are ZinCo greenroofs
utilizing Floradrain FD 25 green roof systems.
Schipholrijk intensive greenroofs - The roof gardens in the neighborhood of Schiphol-airport
located in Schipholrijk measure approximately 10,000 m2 each. Office park area residents
include Microsoft and Mitsubishi. Three of six greenroofs are made with ZinCo system solutions.
Due to the intensive nature of these greenroofs, the ZinCo Elastodrain EL200 system was used
for the driveways, because of the car traffic on the roof. Mixed systems were used on the
remaining roofs using different trademarked drainage and filter material. For example, one roof
garden not pictured here is made with the BACEL-system, a Dutch trademark based on
Styrofoam drainage30.
Large intensive greenroof projects in Schipholrijk; System: ZinCo; Left: Mitsubishi Office Park;
Source: Aart Veerman
Kloten International Airport, Zürich, Switzerland (ZRH)
Zurich-Kloten International Airport in Zürich (ZRH) is the largest airport in Switzerland and
strives to symbolize a modern, comfortable and green airport. ZRH is home to a nature
conservation area that covers an area of approximately 74 hectares and is only a few meters
away from the edge of the runways. ZRH operations and management focus strongly on
communication in the area of environmental protection, and publish an annual environmental
ZRH has two recent large greenroof projects which demanded a high level of effort,
coordination, and communication from all participants because of its sensitive location and
accompanying security measures. No data was found for bird strike counts at ZRH.
Dock E (Dock Midfield) extensive greenroof - One of the largest greenroof building sites in
Switzerland, the new dispatch building at Kloten International Airport is Dock E, previously
known as Dock Midfield, situated between take-off runways and landing strips. Sporting an
extensive greenroof measuring 4,000 m2 (43,056 sf), Dock Midfield represents a perfect
example how green space can be regained on roofs. Completed in November 2002 after years
of detailed discussions, the planning group decided to install ZinCo greenroof systems.
Admittance to the Dock Midfield project was limited to trained staff using registered vehicles,
and strict regulations had to be followed to obey the demanding security measures of airport
ZRH recently seeded in June 2002.
Installing the 80 mm (3”) depth substrate.
Limited movement dictated careful planning, for example one issue dealt with how to bring up
the substrate and gravel to the 18 – 22 m (59 – 72’) high roof surface while crossing a 14 m
(46’) wide photovoltaic installation at the roof’s perimeters without any damage. In response, a
ZinCo partner’s special vehicle utilized a pneumatic pump and placed the substrate materials
onto the roof’s perimeters at three locations, where it was then spread on to the entire surface
using flexible pipes at a depth of 80 mm (3”).
View of ZRH’s Dock E (Dock Midfield) – Up to 27
aircraft can be handled simultaneously ; Source: ZinCo
The ZinCo Green Roof System vegetation
strip next to the 14 m wide photovoltaic
installation. Along the perimeter between
the fascia and vegetation, a safety strip of
gravel is installed as fire prevention.
Source: ZinCo
The roof construction illustrates the not often used variation of the inverted roof in Europe.
Particular to inverted roofs is the fact that the insulation layer is situated over the waterproofing.
“There are two main subjects that have to be taken into consideration when planning a well
functioning Green Roof System on top of an inverted roof,” says Jürgen Ullrich of ZinCo. “First
of all, the insulation material must maintain its insulating effect even during penetration by water.
That means that inverted roofs require extruded insulation. Secondly, the Green Roof build-up
must be designed so that vapour pressure can be built up.”
A flowering meadow-like roof at ZRH three years after installation; Copyright ZinCo
Separation and slip membrane TGV 21 covers the extruded insulation mats and serves as the
base for the ZinCo recycling substrate. TGV 21 is permeable for vapour but resistant to water,
necessary qualities for the installation of a ZinCo Green Roof System on inverted roofs. The
vegetation consists of Sedum shoots at 20 – 25 pieces /m2 (2-3 pieces /sf) which are drought
and frost resistant Sedum plants. Generally, Sedum vegetation is a low demanding type of
vegetation, yet fertilizing and maintenance, especially weeding once to twice/ years, has to be
done. Credits – client: Unique Flughafen Zürich AG; landscape installation: Behlke GmbH;
design company: ARGE Zayetta; project designer and architecture: David Munz; site
supervision and structural engineering: Urs Strickeisen; greenroof systems: System ZinCo;
technical advice: Jürgen Ullrich, ZinCo AG; construction: Behlke GmbH & Co. KG32.
Multi-story Car Park B (Parkhaus B) extensive greenroof –Completed in 2001, the 8,000 m2
(86,111 sf) multi-story Car Park B at ZRH also demanded specific logistic skills and equipment
in bringing up the substrate to the high 50 m (164’) roof level, and a pneumatic pump was
required to blow substrate and gravel onto the roof's surface.
Multi-story Car Park B (Parkhaus B) before
greenroof installation33.
The extensive ZinCo Green Roof System used
here is in its second vegetation season after
Construction work was performed during daily airport vehicle and airplane traffic. The extensive
ZinCo Green Roof System contains a combination of planted Sedum shoots and hydro-seeding
in a sedum carpet. An anti erosion jute control net "JEG" was installed afterwards to protect the
plants against wind uplift34.
The structured grid of sky lights is softened by
the surrounding ZinCo greenroof vegetation
shown three years after installation.
Multi-story Car Park B is now covered by a
carpet of yellow. In the background an
airplane is just taking off.
Credits for the ZRH Multi-story Car Park B - architect and design firm: Stutz & Bolt, Winterthur;
construction: Behlke GmbH, Lennestadt; greenroof system: ZinCo System "Semiramis"35
Frankfurt International Airport, Frankfurt, Germany (FRA)
Germany and Europe’s largest airport, Frankfurt International (FRA) is ranked no. 7 in the world.
At 20 square kilometers (4,942 acres) in size, FRA is also one of the most compact of the larger
world airports36. As a result, one of Frankfurt International’s key issues is ecological land
conservation as they strive for optimum land use with minimal negative environmental impacts
in the densely populated Rhein-Main region.
The maneuvering areas between the taxiways equal approximately 500 hectares and this
nature conservation area has become home for many plants and animals that are endangered
elsewhere. Management techniques include developing part of the area into a heath because
this type of vegetation is the best to minimize the bird strike danger here. The green areas are
not watered and no fertilizer is applied. Rare birds such as the wheatear and whinchat are
observed along numerous endangered toads and frogs with over 300 different plant species
also found on these grounds. In contrast to many other international airports, FRA does not
scare birds but relies on biotope management, which focuses on designing the airport grounds
in such a way that birds are not attracted in the first place. The bird strike count at FRA
averages 3 to 5 per 10,000 aircraft movements and is at the top in terms of international
comparison, equal to the annual strikes at Schiphol International Airport. Furthermore, FRA
operators harvest rainwater from roofs and other surfaces and are committed to nature
conservation by running reforestation programs to make up for land consumed for airport
FRA greenroofs - Plants are used extensively on building facades, within inside courts and on
top of the terminal roofs. Planning and upkeep are usually handled by airport specialists who
run their own airport greenhouse shops. .According to Uwe Harzmann of Optigrün international
AG, Frankfurt International has greenroofs located on Terminal 1 and Terminal 2, on the cargo
building and on Terminal B. The total approximate greenroofed area is 30,000 m2 (323,000 sf)
with Optigrün’s having greened about 11,700 m2 (125,938 sf) of this total. Optigrün estimates
that 2,400 m2 are intensive, and the rest are extensive greenroofs. Optigrün has used the
following substrates depths for these greenroofs: Intensive: (40 – 60 cm 16 – 24”); Extensive 8
– 10 cm (3 – 4”).
Intensive FRA greenroofs by Optigrün international AG38.
The European Experience and Outlook
Not all European countries have experience with airport greenroofs and some officials are
understandably cautious. Referring to airport greenroofs, Dr. John Allan, Head of the Birdstrike
Avoidance Team of the Central Science Laboratory in York, England, believes smaller species
should not present a problem but says “I would be very concerned about the possibility of roof
nesting by gulls, which is becoming an increasing problem here as it is in the U.S.” The question
appears to be whether they would be any more attractive than a bare flat roof39. British
ornithologist and greenroof advocate Dusty Gedge agrees that in parts of the UK there are big
problems with gulls nesting on roofs general. But as director of he believes such
roofs around airports could be beneficial as they would in some way mitigate some of the less
desirable environmental consequences of airports and airlines.40
Yet, Dr. Allan is most interested to hear about existing airport greenroofs elsewhere in Europe,
of which he was not aware. He adds, “We are responsible for checking and approving planning
applications at U.K. civil and military airports in relation to birdstrike issues and, although it has
not happened here yet, the use of greenroofs in Europe suggests that it is a matter of time
before we will need to address this issue in the UK.”41
Greenroofs are simply one sustainable design element incorporated into an overall ecological
airport land use plan. Stormwater retention rates, improved air and water quality, and area
temperature reduction advantages can be expected to have the same effects whether situated
on an airport greenroof or any other landscaped roof, as they are more dependent upon local
climate factors than a type of application. Perhaps since the Europeans have been managing
these natural airport areas with ecological conservation in mind from the start, bird and other
wildlife design considerations and regulations are not separated in terms of natural areas of
taxiways or recreated natural areas on a roof.
Does the European experience indicate birds on greenroofs are causing problems for air traffic
by increasing incidences of bird strikes? Simply, there don’t seem to be any issues pertaining to
increased bird strikes associated with airport greenroofs among any of the manufacturers and
providers contacted within Europe. Not one person identified any specific maintenance
problems or concerns for airport building greenroofs simply because they are located in an
airport – in other words, greenroofs are part of the initial design process and designed according
to the needs of that particular geographic area. Greenroof maintenance is integrated into the
overall airport management plan and is either done by the airport itself or is handled through
landscape contracts with industry professionals.
The respondents argued that birds use greenroofs as much as any other green space in nature,
and usually only small birds settle on greenroofs. Moreover, birds also rest and settle on barren,
naked roofs. Do they cause problems?
A Green Lining
Yes, they do, says Richard A. Dolbeer, PhD, USDA/Wildlife Services National Coordinator,
Airport Safety and Assistance Program, as is illustrated in the photos below. “Based on my
experience evaluating wildlife attractants around airports, I do not believe that properly designed
"green roofs" would attract hazardous birds beyond background levels. In fact, such roofs might
actually reduce the presence of large birds that are hazardous to aviation,” he says. “One
chronic problem that we find around coastal airports in USA and Canada is nesting and roosting
by gulls on flat roofs, especially gravel-covered roofs but sometimes even metal roofs. A survey
we did in 1994 revealed 16,000 gulls nesting on rooftops in cities along the USA portion of the
Great Lakes. This survey missed a lot of roof colonies so the actual numbers were much
higher.” 42.
Traditional flat roofs often do attract hazardous
birds. Left: Ring-billed gulls with chicks
Right: Herring Gulls nest on a rubber
roof. Photos: Richard Dolbeer
He said a similar question about 15 years ago regarding yard-waste compost facilities (would
they attract hazardous birds if located near airports?) resulted in conducting two objective
studies in which bird numbers by species were observed at yard-waste facilities and then
compared to background levels of birds in undeveloped grassy areas of comparable size. They
found fewer birds in the compost areas; thus, yard-waste composting was not incompatible with
aviation safety43.
Richard Dolbeer continues, “Thus, it would be a good idea to have a study conducted to
document the numbers and types of birds seen on green roofs so that you will have objective
data. As I said at the start, I do not think green roofs should attract hazardous birds but the only
way to definitively answer the question is to conduct a study. We already know that traditional
flat roofs often do attract hazardous birds.”44
Successful Design Parameters
Therefore, success appears to be based on various site specific design parameters all directly
relating to the local ecology. Bird species that may form large flocks and feed on airfield
grassland are a concern. Another issue is the possible attraction of pigeons or gulls on roofs
that are used by airport staff during break times when feeding of birds becomes likely. If flat
gravel and barren roofs actually do attract larger birds, it can be argued that greenroofs can be
designed to not attract the larger birds with correct vegetation, and actually deter these more
hazardous types from nesting. Maintenance agreements need to be in place with either airport
personnel or specific greenroof service companies.
One of Germany’s leading landscape architects and foremost expert on greenroofs is noted
researcher and designer Bernd W. Krupka. Mr Krupka advises that construction techniques of
green roof systems must be used against bird populations that are dangerous to aviation, i.e.,
bird species of a larger size than finches. “These construction techniques must provide a higher
growth of the grass and herb vegetation in order to prevent bigger birds from landing on the
roofs, though such areas with higher vegetation must be mowed or cut - the same as any
meadow – in order to prevent shrubs or bushes from growing and to reduce the fire risk. In this
regard it is essential that the airport management provides a job profile which shall also be
applied to the remaining green spaces.” He adds that the subject still needs more research45.
Mr. Krupka contributed the following information: “Bird repelling green roofs can be realized with
extensive and intensive green roof build-ups. For roofs with low load bearing capacities (of
approx. 30 to 40 kg/m²) pre-cultivated vegetation mats made of mosses and herbs (approx. 2040 mm in height) can be used with reinforcement of entangled filaments. Past experience has
shown that birds are deterred by the entangled filaments because of a trap or snare effect.
Higher grass and herb vegetation (approx. 150 to 200 mm in height) is less attractive for birds
as habitats can be created with a substrate depth starting at approximately 150 mm.
For intensive green roofs ground-covering woody plants with low to medium height are
predominantly eligible. There are a number of deciduous and coniferous trees available with no
berries (e.g. Lonicera pileata, Juniperus sabina, Pinus montana). These trees can be
successfully be used for larger green roof areas. However, monocultures should be avoided, as
well as scattered tall trees which are very attractive for birds.
According to past observations, only a few little ground birds like larks or meadow pipits use
extensive green roofs as habitats. On ground-covering woody vegetation types, only greenfinch
or blackbirds have been observed in Germany as breeding birds so far. Gravelled roof areas are
on the other hand in many cases resting places for larger birds: These can be kept off
completely or at least temporary by medium-high vegetation.”46
The Future for ATL and Elsewhere
Interest in smart, energy-efficient buildings has been steadily growing, especially among those
who manage large facilities such as airports because lifetime building operating costs can be
hundreds of times more expensive than the original building itself. Lucie Griggs, director for
Atlanta’s Cool Communities non-profit organization, says NASA's air-quality modeling research
in Atlanta could lead to the creation of financial incentives for doing heat-sensitive construction,
or changes in development laws, which in turn could lead to more possibilities with greenroofs47.
The City of Atlanta is already on track with a greenroof atop Atlanta City Hall with plans for other
government buildings and possible measures to increase greenroof development in the future.
From the successful European experience we can see that certainly greenroofs are viable
alternatives to the average hot, barren airport rooftops, detached from and detracting from our
natural environments. It is easy to understand how Atlanta’s largest urban heat island, Atlanta
Hartsfield-Jackson International Airport, can be significantly mitigated by incorporating
greenroofs, and can serve as a representative scenario of world airport architecture.
Conclusion: A Balancing Act
Using the Airport as a metaphor for the City, it is clear that through utilizing greenroofs as part of
its urban infrastructure of runways, managed greenspaces, etc., we can mitigate many of our
developmental impact ecological problems such as the heat islands, stormwater, habitat
destruction and the like. In a similar vein "underground architect" Malcolm Wells' vision of a new
American landscape includes placing infrastructure underground, and believes even airports
could be located underground. Similarities remain in that humans may reconnect with nature
and each other. In 1994 Wells told The Futurist magazine “The question of how to design an
airport appropriate for the future can be answered as follows: Build huge, high, roofed-over
spaces, allow for floor-to-floor heights of ten feet or more indoors, and pull a blanket of earth
over the whole thing.48
Economic impacts of airport facilities and operations affect many sectors, both private and
public. But we must also balance the needs of current airport land/building management and
expansion plans in environmental impact terms.
Next Steps to a Greener Airport Rooftop Environment
Yet what may appear to be a call for an immediate action or an obvious environmental solution
to the many developmental woes presented by airport construction does need to be tempered
with continued review and research of airport wildlife mitigation design principles at regional
airports worldwide. Our position is to encourage safe, site specific design and maintenance
strategies which include the technology of organic greenroof architecture. Public policy
stakeholders worldwide can benefit from further study of numerous European regional planning
and zoning procedures which include various types of airport greenroofs and systems. We hope
to encourage further dialogue and information sharing between international governments and
bring to light that not only are airport greenroofs possible, they are currently in existence without
mishap. Here then is opportunity to form an international multi-disciplinary team of airport
stakeholders including greenroof design professionals, safety experts, wildlife biologists,
ornithologists, researchers, and government policy makers.
We believe we need to not only embrace this concept, but further study and develop it to best fit
our wide geographic and regulatory needs. Land use practices known to threaten aviation
safety are not acceptable, and agree with Dr. Richard Dolbeer in that we need to have studies
conducted to document the numbers and types of birds seen on existing European airport
greenroofs and representative North American greenroofs across our various climate zones to
accumulate objective data. The FAA will most certainly discourage the development of any
questionable sites, including sustainable greenroofs, if studies show that they support or
encourage potentially hazardous wildlife species. Once local problem bird populations are
clearly identified the judicious selection of the correct vegetation palette should ensure a
comfortable margin safety.
So, in this case, it appears necessary to err on the side of caution before we jump
wholeheartedly into promoting airport greenroofs worldwide. Do we hear any student, policy or
government takers willing to document the European airport greenroof experience, please?
- Linda S. Velazquez and Benjamin Taube
“Are human beings and the natural world destined to be at odds forever? Or can we, so long
estranged from the world that produced us, learn to live as gently, as gracefully, and – with
great good luck – as beautifully here as do all the rest of the world's creatures?” – Malcolm
All rights reserved,, LLC. Permission is granted to Green Roofs for Healthy
Cities to include paper in the proceedings of the Third Annual Greening Rooftops for
Sustainable Communities Conference, Awards and Trade Show, 2005.
Footnotes Page
“Inventor takes airport design to new heights,” by Gary Stoller, USA TODAY 1.12.04
Benjamin Taube and Georgia Tech.
Dr. Jeffrey Luvall, NASA, Personal Communications, 6.01.
Dr. Dale A. Quattrochi, Personal Communications, 6.22.01.
Dr. Jeffrey Luvall, NASA.
Atlanta Department of Aviation.
Grading and Excavating magazine, November/December, 2004.
The natural environmental features of the airfield of Holzdorf and measures for bird-strike
prevention, Bird and Aviation, Vol. 24 (2004), Vol. 1 by K. Hahn-Becker,
November 19, 2001: “FAA Targets Bird-airplane Collisions,” Sacramento Bee, By Matthew
German Bird Strike Committee,
November 19, 2001 – “FAA Targets Bird-airplane Collisions,” Sacramento Bee, By Matthew
Barrows, (
Dan Vergano, USA TODAY,
Sustainable Development at Amsterdam Airport Schiphol 2003 PDF
AART Veerman of the International Green Roof Association and Heidrun Eckert of ZinCo
Landscape Architect Haven Kiers.
AART Veerman of the International Green Roof Association and Heidrun Eckert of ZinCo
2003 Environmental Report, Zurich Airport, April 2004
Jürgen Ullrich, ZinCo Press Report ”Dock Midfield Under a ‘Green Hat’” PDF, October 2004,
prepared for Linda S. Velazquez.
Jürgen Ullrich, ZinCo Press Report “Dock Midfield Under a ‘Green Hat’” PDF, October 2004,
prepared for Linda S. Velazquez.
Uwe Harzmann, Personal Communications, 11.15.04.
Dr. John Allan, Personal Communications, 12.04.
Dusty Gedge, Personal Communications, 12.03.04.
Dr. John Allan, Personal Communications, 12.04.
Dr. Richard Dolbeer, Personal Communications 12.06.04, and Dwyer, C. P., J. L. Belant, and
R. A. Dolbeer. 1996. Distribution and abundance of roof-nesting gulls in the Great Lakes region
of the United States. Ohio Journal of Science 96:9-12.
Dr. Richard Dolbeer, Personal Communications, 12.06.04, and Gabrey, S. W., J. L. Belant, R.
A. Dolbeer, and G. E. Bernhardt. 1994. Bird and rodent numbers at yard-waste compost
facilities in northern Ohio. Wildlife Society Bulletin 22:288-295; Gabrey, S. W. 1997, Bird and
small mammal abundance at four types of waste-management facilities in northern Ohio,
Landscape and Urban Planning. 37:223-233.
Dr. Richard Dolbeer, Personal Communications, 12.06.04.
Bernd W. Krupka, Personal communications, 12.02.04.
Krupka, B.W., Bird and Aviation (ISSN 0721-4521): Flat roofs on airports - advantages by
vegetation. Volume 10, Issue 1 - translated from Bernd W. Krupka by Julia Schumayer of ZinCo
International, 1.12.05.
The Atlanta Journal-Constitution, "NASA studies how to cool area as heat builds up" by Kevin
Duffy of 04/18/04,
48 Natural Life Magazine, # 40.
September/October 1994: The Futurist magazine.