Rob McMonagle, SolarCity Program Manager, Toronto Atmospheric Fund
March 26, 2010
Structural Requirements for Installing a Residential Solar
Water Heater on a Roof
Structural Requirements for Installing a Residential Solar
Water Heater on a RoofThe Toronto Experience The Toronto Experience
Future Events
All webinars run from 1-2:30 p.m. EST
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 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
1. Introduction to Solar Water Heating– Solar Hot Water – A Brief
History– Understanding the
Technology 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
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
7. Open Discussion
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 We’re focusing on solar domestic hot water
(SDHW)
Overview
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
2. Solar on the roof and the Ontario Building Code
Solar as A Designated Structure in the Ontario Building Code 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:
(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?
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) Can we do better?
Design and Structure of Rooftop Solar Projects
Two Issues:– 1. Can roof hold the structure?– 2. Structural mounting of the system
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
Solar on the Roof – Roof Conditions
Two roof types– Flat roof– Sloped roof
Two roof structure types– Rafter– Truss (prevalent in homes built after 1990s)
Two system types– Tank on roof (seasonal)– Tank in the utility room (year-round)
Solar on Sloped Roofs
Solar Neighbourhoods in an older downtown neighbourhood– Older buildings tend to have structurally stronger roofs
Solar on Flat Roofs
Solar Neighbourhoods in an older downtown neighbourhood– 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 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
Typical Weights on Roof
Area (m2)
Full Load (kg)
Distributed Load (psf)
SDHW Collectors
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
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? 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
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...
Some solar hot water collectors are close to weight (3.3 – 5.3 vs. 3.8 for shingles) so there are some opportunities
The “Toronto Solution” 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
Span Table
– Sample load calculation (for review by Toronto Building)– Letter of conformance by P. eng.
Solar Thermal Structural Load Span Table
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
Product Span Tables are dependent on collector specs (weight) but also mounting methodology
Enerworks ThermoDynamics CC Solar Greensaver
collector flat plat flat plate evacuated tube tank on roof
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 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
Verification of Roof Capacity for Truss Roofs 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
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
Process for Roof Verification
Develop Product Span
Table
Roof Structure
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
Install
Roof Structure Needs
Upgrading
Install
No Yes
InstallRoof Structure
Needs Upgrading
Install
RafterTruss
Verification of Roof Conditions Inspection requirements will vary
depending on type of roof – rafter or truss
Rafters are easier to verify as they are defined in the Ontario Building Code
Toronto Solution for Rafters – Solar Roof Report
Roof inspection report is done showing the conditions of the roof at site of proposed solar installation
Roof Report – who does? Under the OBC the homeowner is
exempt from requirement to be a qualified designer
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
Solar Neighbourhoods has developed a Bulletin Guide on methodologies to assess roof conditions – i.e. How to measure
roof rafter sizes Will be posted on
website soon
Solar Neighbourhoods Experience
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)– 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 Solar
Projects
Actual Rafter Spans
(Average) (m)
Max. Rafter Span Allowed (Average) (m)
“Extra” Rafter Span
(Difference) (m)
Difference (%)
Flat Roof 27 3.73 4.87 1.14 30.5%Sloped Roof 38 3.69 4.81 1.12 30.2%
Level of Concern
The proof of conformance to the Ontario Building Code should be linked to the level of potential structural concern
System Type Roof Type
Sloped FlatCollectors mounted flush Collectors mounted on a rack
Seasonal (tank of roof)
Medium Major
Year around (drain back or closed loop)
Minor Medium
The Cost of Regulatory Compliance for Roof Mounting
Item Rafter Roof Truss Roof Contractor Time
Mounting Structural Drawings and Span Table
$700 - $2,000Done 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)
$600 1 hr
Total $0 $600 1 hr
Some Possible Next Steps to Reduce Structural Concerns Solar manufacturer’s can reduce weight of there collectors
– Some are close to weight limit already
Document more roof conditions (rafter and truss)– Is there an actual problem? Initial indicators are it is not
Analyze the OBC roof structural requirement– Is there already capacity to allow solar collectors onto roofs built to the OBC?
Solar Ready Roofs– 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
Thank you
Thanks to the Ontario Ministry of Energy and Infrastructure and Natural Resources Canada for their support of this project
City of TorontoContacts
Rob McMonagle SolarCity Program ManagerToronto Atmospheric Fund
www.SolarPermits.ca
Solar Neighbourhoods Information Line
416-393-6370 www.solarneighbourhoods.ca
Toronto Buildingwww.toronto.ca/building