Ground-mount and flat-roof solar

Most Canadian solar goes on pitched roofs, but it is not the only option. Flat roofs and open yards can both host good systems. Each comes with its own racking, permits and costs.

Flat-roof solar

Flat roofs are common on modern homes, additions, garages and some older urban houses. Panels can't lie flat, because they would collect snow, dirt and water and produce less. Instead they sit on racking that tilts them up.

Ballasted racking

Ballasted systems hold the panels down with weight, usually concrete blocks, instead of bolting through the roof.

• Few or no roof penetrations, which lowers leak risk
• Adds a lot of weight, so the roof structure must be checked by an engineer
• Usually uses low tilt angles to reduce wind load
• Needs a roof membrane in good condition, with protective pads under the racking

Attached racking

Attached systems are fastened to the roof structure with sealed mounts.

• Lighter than ballasted systems
• Allows steeper tilt angles and better wind resistance
• Every penetration must be properly flashed and sealed, ideally by or with a roofer familiar with your membrane

Some systems combine the two, using a little ballast and a few attachments.

Tilt on flat roofs

Flat-roof arrays usually use tilts of roughly 5 to 15 degrees. Steeper tilts capture more sun per panel, but rows must be spaced further apart to avoid shading each other in winter, so fewer panels fit. Low tilts let you fit more panels in the same space, with slightly less output per panel. An installer will balance the two for your roof.

Natural Resources Canada's solar maps show how output changes with tilt in your area, including horizontal, latitude tilt and vertical.

Ground-mount solar

Ground mounts put panels on a frame in your yard, usually anchored with posts or screws into the ground.

Advantages

• You can choose the ideal direction and tilt, often close to due south at a steeper angle than your roof
• No roof penetrations, and the roof can be replaced without touching the panels
• Easier to clear snow and inspect
• Can be placed away from shade
• Bifacial panels can pick up reflected light from snow on the ground

Drawbacks

• Takes up yard space
• Usually costs more per watt, because of the frame, foundations and trenching to run cables to the house
• Panels at ground level may need fencing or protection in some settings
• Zoning rules can limit placement and height

Green Building Canada lists ground-mounted solar as an option that may call for a zoning review in Toronto. Expect ground mounts to cost more than a simple roof system, and get quotes for both if you are deciding.

Snow

Snow affects both types.

• Flat-roof arrays at low tilt shed snow slowly. Snow can also drift between rows. Plan for lower winter output.
• Ground mounts can be set at steeper angles, which helps snow slide off, and leave enough clearance underneath so snow doesn't pile up against the bottom edge.

Winter production is a small share of the yearly total in most of Canada. In our Toronto sample system, November to January produce about 7% of annual output. See solar panels and snow.

Permits

Permit rules vary by municipality. Toronto's rules are a useful example:

• Rooftop systems larger than 5 square metres need a building permit, with structural calculations from an Ontario-registered engineer.
• Free-standing ground-mounted systems don't need a building permit in Toronto, but zoning bylaws still apply, and the city suggests a zoning review first.

Every system, roof or ground, also needs an electrical permit and inspection, plus utility approval to connect. See permits and connecting to the grid. Check your own municipality's rules, since rural townships and other cities differ.

Cost compared with a pitched roof

These are general patterns, not fixed rules. Compare quotes using price per watt. See how to compare solar quotes.

When each makes sense

• Flat roof in good condition with a sound structure: a flat-roof system can work well.
• Flat roof near the end of its life: replace the membrane first. See replacing your roof before solar.
• Shaded or poorly oriented roof, with open sunny yard space: a ground mount may produce more and pay back faster despite the higher cost.
• Rural property: ground mounts are common and often simple to permit.

Next step

Check your roof to estimate production, then use the system size tool to see what size fits your space.

Common questions

Can you put solar panels on a flat roof?

Yes. Panels go on tilted racking that is either held down with ballast or attached to the roof. An engineer should confirm the roof can carry the weight and snow load.

Do I need a permit for a ground-mounted solar system?

It depends on your municipality. Toronto doesn't require a building permit for free-standing ground mounts, but zoning still applies, and every system needs an electrical permit and inspection.

Is ground-mount solar more expensive than rooftop?

Usually, because of the frame, foundations and trenching. Better orientation and no shade can make up some of the difference in production.

What tilt is best for flat-roof solar in Canada?

Flat-roof arrays commonly use about 5 to 15 degrees. Steeper tilts produce more per panel but need wider row spacing, so your installer will balance output against panel count.

Sources

• City of Toronto: Building permit guide for solar collectors
• Natural Resources Canada: Photovoltaic potential and solar resource maps of Canada
• Green Building Canada: Solar panel cost in Canada