Structural Requirements for Installing a
Residential Solar Water Heater on a Roof
The Toronto Experience
Rob McMonagle, SolarCity Program Manager, Toronto Atmospheric Fund
March 26, 2010
Future Events
All webinars run from 1-2:30 p.m. EST
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Webinar 1 – Developing a Building Permit Process for Solar
Water Heating - Wednesday, March 24
Webinar 2 - Structural Requirements for Installing a
Residential Solar Water Heater on a Roof - Friday, March 26
Webinar 3 - Inspecting Residential Solar Water Heating
Systems - Wednesday, March 31
Webinar 4 - Permitting of Residential Solar Water Heating
Systems - Wednesday, April 14
NOTE: All presentation will be posted on www.solarpermits.ca a few
days after the webinar
Solar Permits Overview
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Developed by the Toronto Atmospheric Fund (TAF) to share
knowledge gained through the largest single-city solar hot
water project in Canada (Solar Neighbourhoods).
TAF is the City of Toronto’s climate agency. TAF supports the
development and implementation of leading-edge ideas with
the potential for large emission reductions.
TAF is working to support greater deployment of renewable
energy in Toronto as a way of helping the City reach its
emission reduction targets.
Solar Permits is made possible by an investment by the
Government of Ontario and the Government of Canada.
Webinar Agenda
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1. Introduction to Solar Water
Heating
– Solar Hot Water – A Brief
History
– Understanding the Technology
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2. Solar on the Roof and the
Ontario Building Code
3. Roof Conditions & Solar
Systems
4. Solar Span Tables
5. How to Verify Roof
Conditions for Truss Roofs
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6. Verification of Roof
Conditions for Rafters
5. Verifying That the Roof can
Support Solar
6. Supporting Solar - Is it a
Concern?
– Toronto’s experience
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7. Open Discussion
1. An introduction to
solar water heating
Solar Technologies

There are four distinct technologies that collect
energy from sunlight
– Passive Solar – collects heat and light through natural
(passive) processes
– Photovoltaic or PV – produces electricity directly as a
result of the material’s properties
– Solar Air – produces hot air for space heating
– Solar Water – produces hot water for pools, industry and
residential applications
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We’re focusing on solar domestic hot water (SDHW)
Overview
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For an overview of solar hot water in
Canada and internationally, please see
webinar #1.
2. Solar on the roof and
the Ontario Building
Code
Just how heavy is that solar
system on my roof?
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Could this be an actual concern????
Solar as A Designated Structure
in the Ontario Building Code
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1.3.1.1 Designated Structures
– The following structures are designated for the purposes of clause (d) of
the definition of buildings in subsection 1(1) of the Act:
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(f) A solar collector that is mounted on a building and has a face value equal
or greater than 5m2.
However - where solar modules are supported by and are connected
to a building they are covered by the Building Code (regardless of
size) – thus there is a need to carry out a review for conformance.
Requirement to review
– Can the roof withstand the extra load? (both dead and uplift (wind))
– Will the solar collectors stay attached to roof?
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International best practices
– Its not a problem (Europe) – but roofs are built to higher standards
– Ignore it OR require an engineers report for each installation (US &
Canada)
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Can we do better?
Design and Structure of
Rooftop Solar Projects
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Two Issues:
– 1. Can roof hold the structure?
– 2. Structural mounting of the system
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How is it going to be installed on the roof?
– Can be dealt with through a P.Eng stamped
structural drawing of the system mounting
(supplied by manufacturer)
– If the design is used for multiple projects, it does
not need to be a stamped drawing for a single
project
Example Structural Mounting
Drawing
3. Roof conditions and
solar systems
Solar on the Roof – Roof
Conditions
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Two roof types
– Flat roof
– Sloped roof
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Two roof structure types
– Rafter
– Truss (prevalent in homes built after 1990s)
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Two system types
– Tank on roof (seasonal)
– Tank in the utility room (year-round)
Solar on Sloped Roofs
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Solar Neighbourhoods in an older downtown
neighbourhood
– Older buildings tend to have structurally stronger roofs
Solar on Flat Roofs
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Solar Neighbourhoods in an older downtown neighbourhood
–
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About 30% of installations done on flat roofs
Higher concern of water leakage
Increased wind loading
Variety of roof covering
Seasonal Systems with
tank on Roof
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Limited experience in Solar Neighbourhoods as no
sales of this product were made
– However the developed product span table for one
seasonal system is comparable to span tables for systems
with just the collector on the roof
– Seasonal systems are about ½ the size of year-round
systems
This is Not Just a Solar Hot
Water Issue
This Would Have Serious Uplifting
Load Issues
(perhaps its designed as a house that can fly?)
Typical Weights on Roof
Area
(m2)
Full Load (kg)
Distributed
Load (psf)
Globe (tank on roof)
3.5
270
15.7
CC Solar
5.3
140
5.3
Linuo Paradigma
4.6
107
4.7
Viessmann
5.0
94
3.8
EnerWorks
5.7
105
3.7
Thermodynamics
5.9
95
3.3
Solar Pool Heating Collectors
3.8 each
17
0.9
Photovoltaic Solar Modules
1.2 each
14
2.4
SDHW Collectors
Standard Asphalt Shingles - 190 lbs/100 ft
1.9
Asphalt Shingles - 2 layers of shingles
3.8
Weight of average Canadian male
(codified structural live load for a worker)
83
20.8
Prefab Chimney - 7" dia. per 3' section
21
46
Where to Draw the Line?
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If the solar collectors weigh similar to other products with
long term use on roofs (i.e. 2 layers of shingles) then they are
structurally acceptable due to past equivalent satisfactory
performance. Toronto Building Official
Thus PV modules and solar pool collectors (unglazed) fall
below the weight if mounted flush to roof
– However there still is a concern about roof connections
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Toronto Building has yet to make a definitive ruling about the
need for a structural building permit for PV and pool collectors
– But hopefully soon...
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Some solar hot water collectors are close to weight (3.3 – 5.3
vs. 3.8 for shingles) so there are some opportunities
4. Solar Span Tables
The “Toronto Solution”
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City of Toronto’s Building Department has
developed a simple methodology to determine if
the roof conditions can withstand the structural
loading of the renewable energy projects for rafter
roofs
Truss roofs require a different solution
Step 1: Development of product structural
drawings
– Stamped structural drawings
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Span Table
– Sample load calculation (for review by Toronto Building)
– Letter of conformance by P. eng.
Structural Drawing
(example)
Structural Drawing
(example)
Sample Load
Calculations
Engineer’s
Letter of
Conformance to
OBC
Solar Thermal Structural Load
Span Table
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As part of the
structural drawing
a span table is
developed showing
the types of roof
conditions that the
product can be
installed on
Product Span Tables
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Product Span Tables are dependent on collector
specs (weight) but also mounting methodology
Enerworks
ThermoDynamics
CC Solar
Greensaver
flat plat
flat plate
evacuated tube
tank on roof
collector
rafter spacing
16"
24"
16"
24"
16"
24"
16"
24"
2×4
3.71
3.01
2.59
2.18
1.69
1.74
2.24
2.02
2×6
5.38
4.35
3.64
3.04
2.52
2.56
3.77
3.32
2×8
6.60
5.34
4.42
3.68
3.18
3.17
4.92
4.28
2×10
8.14
6.59
5.43
4.50
4.08
3.98
6.41
5.51
2×12
9.49
7.69
6.32
5.23
4.89
4.69
7.73
6.60
Solar Neighbourhoods Standard
Structural Drawings
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Once the methodology was proven there was sufficient comfort level
at Toronto Building to use a standard drawing for all solar collectors
with similar conditions
Solar Neighbourhoods developed standard sloped roof span tables
for flat plate collectors
–
–
This standard drawing is a publicly available document that can be used for any
solar collector
A possible future step would be to turn this into a “standard construction detail”
(similar to prefab chimneys or wooden decks) through TACBOC or LMBOC
standard - 6 connections
standard - 8 connections
rafter spacing
16"
24"
16"
24"
2×4
2.68
2.28
2.74
2.30
2×6
3.78
3.18
3.89
3.23
2×8
4.61
3.86
4.74
3.92
2×10
5.68
4.74
5.84
4.81
2×12
6.63
5.52
6.80
5.59
Solar
Neighbourhoods
Standard
Drawings Letter
of Conformance
5. How to verify roof
conditions of truss
roofs
Verification of Roof
Capacity for Truss Roofs
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Trusses are an engineered product – not listed in
the OBC
Two methods identified that can verify that the
truss has the additional structural capacity to hold
solar collectors
– Verification from the manufacturer
– Site report from a structural engineer
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There are engineers that specialize in truss inspections
Reported experience from some solar contractors is that the
cost of site inspection by truss engineer costs $600
Structural
Engineer’s
Report
Structural Engineer’s Report
6. Verification of Roof
Conditions
Process for Roof
Verification
Develop Product
Span Table
Truss
Roof Structure
Rafter
Roof Report by
P.Eng
Roof Report by
Contractor
Load Calculation
by P.Eng
Verify vs. Span
Table
Verify vs. Span
Table
OK?
No
Yes
No
Roof Structure
Needs Upgrading
Install
Roof Structure
Needs Upgrading
Install
Install
Yes
Install
Verification of Roof
Conditions
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Inspection requirements will vary
depending on type of roof
– rafter or truss
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Rafters are easier to verify as they are
defined in the Ontario Building Code
Toronto
Solution for
Rafters – Solar
Roof Report
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Roof inspection
report is done
showing the
conditions of the
roof at site of
proposed solar
installation
Roof Report – Specs
looking for
Roof Report – who does?
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Under the OBC the homeowner is exempt
from requirement to be a qualified designer
Last Step
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Verify that the solar span table is
inside the actual roof conditions
Verify that roof conditions are
greater than product span table
If the roof is composed of 2x8 rafters on 16” (400 mm) spacings then this
solar collector can be installed on a maximum rafter span of 3.18 m with
no structural alterations
However this does not work for truss roofs
How to Assess A Roof for
Conditions
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Solar Neighbourhoods
has developed a Bulletin
Guide on methodologies
to assess roof conditions
– i.e. How to measure roof
rafter sizes
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Will be posted on
website soon
7. Supporting solar –
Is it a concern?
Solar Neighbourhoods
Experience
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Through Solar Neighbours, TAF has evaluated 65 Roof Reports
Only 1 project ran into structural challenges (rafter span greater than required by
the solar span table)
–
–
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Project was able to proceed by moving the collectors onto the flat roof
No contractor reported that a sale was lost due to inadequate roof structural conditions
On average project roofs had a 30% greater rafter span than required by the solar
span table
It appears that for downtown Toronto roofs have adequate structural capacity to
hold solar collectors without any required structural modifications
Number of Actual Rafter Max. Rafter “Extra” Rafter Difference
Solar
Spans
Span Allowed
Span
(%)
Projects (Average) (m) (Average) (m) (Difference) (m)
Flat Roof
Sloped Roof
27
38
3.73
3.69
4.87
4.81
1.14
1.12
30.5%
30.2%
Level of Concern
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The proof of conformance to the Ontario
Building Code should be linked to the level
of potential structural concern
System Type
Seasonal (tank of roof)
Year around (drain
back or closed loop)
Roof Type
Sloped
Flat
Collectors mounted flush
Collectors mounted on a rack
Medium
Major
Minor
Medium
The Cost of Regulatory
Compliance for Roof Mounting
Item
Mounting Structural Drawings and
Span Table
Rafter Roof
Truss Roof
$700 - $2,000
Done by a P.Eng - Only done once
Should be done by manufacturer or standard
construction details developed by regulator
Roof Structure Report
?
1 hr
Structural Roof Report (down by
Structural Engineer)
Total
Contractor
Time
$0
$600
1 hr
$600
1 hr
Some Possible Next Steps to
Reduce Structural Concerns
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Solar manufacturer’s can reduce weight of there collectors
– Some are close to weight limit already
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Document more roof conditions (rafter and truss)
–
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Analyze the OBC roof structural requirement
–
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Is there already capacity to allow solar collectors onto roofs built to the OBC?
Solar Ready Roofs
–
–
–
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Is there an actual problem? Initial indicators are it is not
Change the OBC to make new roofs (rafter and truss) “solar ready.”
Work with new home builders to make homes “solar ready”
Work with truss manufacturers to make “solar ready” trusses
Develop standard construction details for solar collectors
–
Which eliminates cost of companies developing P.eng stamped structural drawings
8. Discussion
Thank you
Thanks to the Ontario Ministry of
Energy and Infrastructure and Natural
Resources Canada for their support of
this project
City of Toronto
Contacts
Rob McMonagle
SolarCity Program Manager
Toronto Atmospheric Fund
416-393-6371
rmcmonagle@tafund.org
www.SolarPermits.ca
Solar Neighbourhoods
Information Line
416-393-6370
www.solarneighbourhoods.ca
Toronto Building
www.toronto.ca/building