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

1. An introduction to solar water heating

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 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

Just how heavy is that solar system on my roof?

Could this be an actual concern????

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

Example Structural Mounting Drawing

3. Roof conditions and solar systems3. Roof conditions and solar systems

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

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)

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

4. Solar Span Tables4. Solar Span Tables

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.

Structural Drawing (example)

SAMPLE

Structural Drawing (example)

SAMPLE

Sample Load Calculations

SAMPLE

Engineer’s Letter of Conformance to OBC

SAMPLE

SAMPLE

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

Solar Neighbourhoods Standard Drawings Letter of Conformance

5. How to verify roof conditions of truss roofs

5. How to verify roof conditions of truss roofs

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

Structural Engineer’s Report

SAMPLE

Structural Engineer’s Report

SAMPLE

6. Verification of Roof Conditions6. Verification of Roof Conditions

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 – Specs looking for

Roof Report – who does? Under the OBC the homeowner is

exempt from requirement to be a qualified designer

Last Step

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

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

7. Supporting solar – Is it a concern?

7. Supporting solar – Is it a concern?

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

8. Discussion8. Discussion

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

416-393-6371rmcmonagle@tafund.org

www.SolarPermits.ca

Solar Neighbourhoods Information Line

416-393-6370 www.solarneighbourhoods.ca

Toronto Buildingwww.toronto.ca/building