Which roof types work best for solar panels?

Your roof is the foundation of a solar system, and it is also the part most likely to cause regret if it is overlooked. The good news is that nearly every common Canadian roof can carry panels. The less comfortable news is that each type has its own quirks, and the age of the roof usually matters more than its material. This guide is part of our installation and installers hub and complements the quick checks in our roof suitability checklist.

Asphalt shingle roofs

This is the most common roof in Canada and the one installers know best. Panels sit on rails that are bolted through the shingles into the rafters, with flashing under and around each attachment so water cannot find its way in. Done properly, the roof stays as watertight as before.

What to watch: shingle condition. Brittle or curling shingles are hard to flash neatly, and an old roof will need replacement during the panels’ lifetime. If your shingles have more than a decade or so left, you are usually fine. If not, replace first. Ask the installer how they flash each mount and what the workmanship warranty says about leaks.

Metal roofs

Metal roofs are popular for solar because they are durable and the panels last about as long as the roof. How panels attach depends on the profile.

On standing-seam metal, installers often use clamps that grab the raised seams, so no holes are drilled in the roof surface. That removes the most common leak risk. Corrugated and exposed-fastener metal roofs need mounts that attach through the panel with sealing washers or blocks, so the leak risk is similar to shingle roofs, and the sealing details matter. Some metal coatings and warranties can be affected by attachments, so check with the roofing manufacturer or the roofer before you commit.

Snow tends to slide off smooth metal quickly, and panels on top may shed it even faster. That can be a plus for winter output, but it also means snow can drop suddenly, so consider how it will fall around doors and walkways.

Tile and slate roofs

Clay, concrete and slate tiles are heavier and more fragile. Mounts typically replace or sit beneath individual tiles, using hooks that attach to the rafters. Installers must lift tiles without cracking them, and broken tiles are a real possibility, so confirm that spares are available or that the installer will source matches. Work on these roofs tends to cost more and to need more experienced crews. Ask to see photos of earlier tile installs.

Flat and low-slope roofs

Flat roofs, common on additions, garages and some town houses, are mounted on tilted frames. The two main methods are ballast, where weight holds the frame in place, and mechanical attachment through the membrane. Ballasted systems avoid penetrations but add load, so a structural check is part of the job. Mechanically attached systems need careful sealing into the membrane.

Tilting panels helps with snow shedding and improves winter output. It also means row spacing matters, because each row can shade the next when the sun is low. Drainage and access for roof maintenance should be preserved, and a roofing contractor familiar with the membrane should sign off on penetrations so the roof warranty is not voided.

Roof age and condition

Solar panels commonly carry performance warranties of around 25 years. If a roof needs replacing in five years, panels have to be removed, stored and reinstalled, which is often a substantial cost. Replacing the roof first, or at the same time, is usually cheaper than doing it later. A roofer can estimate remaining life honestly, and an installer who is also a roofer may give a bundled quote, so compare it with separate prices.

Also check the structure. Panels add modest weight per square metre, but older roofs with sagging rafters or past water damage need attention. Many installers will not proceed over a damaged deck.

Penetrations, leaks and warranties

Every attachment is a possible leak path, so the quality of flashing and sealing matters more than the roof type. Ask these questions:

• How is each mount flashed, and with what materials?
• Is there a separate warranty for roof penetrations, and how long does it last?
• Who is responsible if a leak appears, and does the roofing warranty stay intact?
• What happens to the roof if the panels must be removed?

Get the answers in writing. Many roofing problems blamed on solar are really old shingles or poor sealing at one or two attachments.

Orientation, pitch and shade

Roof type interacts with direction and slope. South is best, and east or west slopes work at somewhat reduced output. A steeper pitch helps shed snow, while a shallow roof may collect more of it. Shade from trees and chimneys matters more than compass direction. Heavy hail and wind are also considerations in some regions, which we cover in solar, hail and weather in Canada.

If the roof is poor, a ground mount or carport may be a better idea. Our comparison of roof, ground and carport mounting explains the trade-offs. When you are ready to see how the work unfolds, read solar installation step by step, and keep a copy of the roof and flashing details for your yearly maintenance checklist.