Solar for Barns and Farm Shops: What Roof Do You Actually Need?

Every farm has a big south-facing roof, and every installer would rather use it than dig footings. But the roof that looks perfect from the laneway can fail in four ways once someone gets a tape measure and an engineer on it. This guide gives you the numbers to run that check yourself before the quotes arrive.

It is written for Canada, where snow is the load that matters and the National Farm Building Code lets older barns be built lighter than houses. Use the five tests below before you sign a rooftop install contract.

Start with the panels. Most modules sold in Canada in 2026 are rated 400 to 480 watts and measure roughly 18 to 25 square feet. A Canadian-built Silfab 440 W module, for example, is 67.8 by 44.6 inches — about 21 square feet. That works out to 19 to 21 watts per square foot of panel.

You never cover the whole roof. Rows need gaps, ridges and eaves need setbacks, vents and stacks get in the way, and many authorities want a clear pathway for firefighters. After those losses, a realistic layout lands at 12 to 16 watts per square foot of roof plane. Formula: roof plane needed = system size in watts ÷ 12 to 16 W per ft².

The panels will be up there for 25 years or more. The roof has to outlast them, or you pay to take the array down and put it back up.

• Standing-seam steel — best case. Clamps grip the raised seam with set screws. No holes, no sealant, and the roof warranty stays intact.
• Exposed-fastener steel (the corrugated / ribbed sheet on most Canadian pole barns) — brackets screw through the high rib into the purlin. Good brackets come with factory-applied butyl sealant and are reliable when installed well, but each screw is a penetration. Check the roof warranty before you commit.
• Asphalt shingles on a shop or older barn — need flashed mounts and a roof with 20+ years left. A 15-year-old shingle roof should be replaced first.
• Wood shakes or rusted, oil-canned steel — no. Reroof or go to the ground.

Age matters more than material. Ask for the roof's install date, look at the fasteners for rust bleed, and check the underside of the deck for staining. A roof that is dry and tight at 12 years old is a candidate. One that has been patched twice is not.

This is the test people skip, and the one that matters most in Canada.

A flush-mounted array adds about 3 to 4 pounds per square foot: 2.2 to 2.7 for the panels and the rest for rails and clamps. Natural Resources Canada's "PV Ready" guideline uses 0.17 kPa, or 3.5 psf, as the design number. On its own that is small. The problem is what it does to snow.

The array itself is a light load. Ground snow loads across Canada are ten to thirty times heavier, and panels can change how much of that snow stays on the roof. Three things the engineer will look at:

1. What the trusses were designed for. The National Farm Building Code of Canada 1995 lets farm buildings of "low human occupancy" (no more than one person per 40 m²) be built to relaxed structural requirements. Many pole-barn trusses are designed to an agricultural loading in the range of 25 psf snow — lighter than a house. The code's structural rules have not been updated since 1995, so an older barn may have less reserve than you assume.
2. Whether the roof stays slippery. Ontario's rooftop solar guidance for rural buildings says the engineer must decide if the roof is windswept and if it will be slippery after the modules go on. Bare steel sheds snow. Panels at a low angle can hold it, which raises the design snow load on that part of the roof and can pile drifts against the array's edges.
3. Point loads versus spread loads. Rails attach at set spacings, so the weight of the panels and any snow on them reaches the trusses at specific points, not evenly. The engineer models whether each truss connection can take it. Reinforcement, when needed, is usually added purlins, truss bracing or a few sistered members — a small line on a six-figure project.

Most Canadian barns are 3/12 or 4/12. A 4/12 roof is 18.4 degrees. On annual output alone that is fine: flush-mounted panels on a 4/12 roof lose only a few percent a year compared with the ideal tilt. The issue is winter.

Panels below about 15 degrees do not shed snow well, and any array below 40 degrees will carry snow for a while after a storm. On the Prairies and in central Canada that can mean weeks of near-zero output in January.

How much that costs depends on your export rules. In a province with 1:1 net metering (Ontario, Nova Scotia, New Brunswick, PEI, Newfoundland, Quebec), summer credits carry you through winter and the loss is small. In Saskatchewan or Manitoba, where exports earn a low fixed rate, winter self-consumption is worth more and a low roof hurts. A ground mount set at 35 to 45 degrees sheds snow fast and produces 10 to 25% more per panel than a low roof.

Poultry, dairy and hog barns push out ammonia. Concentrations of 50 to 200 parts per million are normal in barn air, and higher at the exhaust fans. Ammonia plus moisture corrodes the metal contacts inside a module, its frame and its junction box.

The industry test for this is IEC 62716, which exposes modules to concentrated ammonia for 20 days. Ask for the test report, not just a claim. And keep the array and the inverters away from the exhaust side of the building.

1. Is the south or west roof plane at least 6,000 ft² for 100 kW (or 3,000 ft² for 50 kW)? No → ground mount, or a smaller system.
2. Does the roof have 20+ years left, ideally standing-seam or sound steel? No → reroof first, or ground mount.
3. Has a structural engineer confirmed the trusses carry 3-4 psf more plus your snow load? No → reinforce, or ground mount.
4. Is the pitch 4/12 (18°) or steeper, so snow can shed? No → expect a longer snow-covered season; a ground mount at 35-45° sheds better.
5. Is it a livestock barn with ammonia exhaust near the array? Yes → specify IEC 62716 ammonia-rated modules, or mount elsewhere.

If any test fails, price the ground mount. It costs more per watt for three reasons: racking on driven piles or concrete footings, a trench for the cable run to the barn's electrical room, and a fence if the array is accessible to people or livestock.

On fencing

The Canadian Electrical Code does not demand a fence around every ground mount. It requires the wiring to be inaccessible to the public. Ontario's Electrical Safety Authority accepts wiring in a raceway, wire screening as a barrier, open wiring kept at least 2.5 metres above grade, or a fence that meets the Code's fencing rules. On a working farm the practical driver is usually livestock and equipment, not the Code. A pasture array gets a fence. An array behind the shop often does not.

• Building permit for the structure, with an engineer's letter. Ontario spells this out for farm buildings; check your municipality elsewhere.
• Electrical permit under Section 64 of the Canadian Electrical Code. Arrays on buildings need rapid shutdown: circuits more than one metre from the array must drop to 30 volts within 30 seconds when a firefighter hits the switch.
• Utility interconnection before you buy, so the export rate is locked and the transformer can take it.
• Insurance. Tell your insurer before installation and get written confirmation. Some Canadian policies exclude hail or wind damage to panels — make sure yours does not.

A real example of the roof route done right: in March 2025 the North Bay Nugget reported on the Lauffer family in Armour Township, Ontario, who put 38 panels — about 10 kW — on their barn roof and now cover most of their farm power. Small, on an existing roof, and paying off. That is the shape of most successful farm installs.

Every barn is different. Roof pitch, orientation, age, material, whether it's a livestock building — all of it changes whether the roof or a ground mount is the cheaper path. Our farm calculator asks four short questions and returns a personalised system size + payback estimate you can take straight to installer quotes.

• Government of Ontario — Rooftop solar installations on rural buildings; Building permit requirements for farm buildings
• National Research Council Canada — National Farm Building Code of Canada 1995; Daily Commercial News, Engineer reviews proposed farm building regulations in NBC 2020
• Natural Resources Canada — Photovoltaic Ready Guidelines (0.17 kPa dead load)
• NBC 2020 ground snow loads via Roofing Calculator HQ and Flat Roofing Insights
• Silfab Solar — SIL-440-QD specifications; Heliene — module range
• SurgePV — Rooftop solar structural assessment; Roof pitch performance; The Green Watt — Panel weights and roof load math
• Greentech Renewables — Guide to metal roof solar installation
• TNLab — IEC 62716 ammonia corrosion testing; EGE — Ammonia corrosion in farm solar
• Electrical Industry News Week — Guide to CE Code Section 64; Alberta STANDATA — Rule 64-218 rapid shutdown; ESA — Bulletin 64-4-4
• Green Building Canada — Solar panel cost in Canada 2026; NerdWallet, Ground-mounted solar cost; EnergySage — Ground-mounted solar
• HomeGuide — Trenching cost; Barrier Boss — Chain link fence cost Canada; SurgePV — Solar land area
• North Bay Nugget — Solar panels on barn roof pays off for Armour families, March 18, 2025
• ThinkInsure — Solar panels and insurance in Canada