Snow and wind loads: what your site's climate data means for a fabric building

A fabric building that performs well in Lethbridge can be under-designed in Fort McMurray. The frame, the cover and the anchors all depend on two numbers that change from one town to the next: the snow load and the wind load at your site. This article explains where those numbers come from and why they matter when you compare quotes.

Where the numbers come from

The National Building Code of Canada publishes climatic design data for hundreds of locations. For each one, it lists a ground snow load, a rain load that can sit on top of snow, and a reference wind pressure. Provinces that adopt their own code, such as the BC Building Code or the NBC Alberta Edition, use the same approach.

An engineer starts with the values for your location, then adjusts them for the building itself: its shape, its exposure, its height, and its importance category. A storage building and a building people work in all day are not held to the same standard.

Snow: it’s not just how much falls

Ground snow load is only the starting point. What matters to an arched or gable fabric structure is how snow behaves once it lands.

• Unbalanced loading. Wind strips snow from one side of an arch and piles it on the other. The frame has to carry that lopsided load, not just an even blanket.
• Drifting. Snow builds up against taller neighbouring buildings, against end walls and in valleys between structures. A building placed beside a taller shop can see far more snow than the code value suggests.
• Sliding. Snow sheds off curved covers and piles against the sidewalls and doors. Door placement and clearances need to account for it.

This is why “rated for X psf” in a brochure doesn’t tell you much. The engineering has to reflect where the building sits and what’s around it.

Wind: uplift is the hidden load

Most people picture wind pushing on the side of a building. For fabric structures the bigger concern is often uplift: wind flowing over the curve of the roof creates suction that tries to lift the whole structure. That load goes straight into the anchors and the foundation.

Open doors change the picture again. A large opening on the windward side pressurizes the inside of the building and adds to the uplift. If your operation leaves doors open, tell the engineer, because it affects the design.

What a generic rating misses

A building sold off a price list is usually engineered for a typical set of loads. That can be fine, or it can leave you short on frame spacing, cover strength or anchor capacity for your site. The gaps tend to show up in the first hard winter: a frame that deflects, a cover that ponds or tears, anchors that pull.

Site-specific engineering costs little compared with the building, and building departments increasingly require it. Sealed drawings tied to your location’s climatic data are what get a permit issued.

What to send us

To quote a building that’s engineered for your site, we need:

1. The site address or legal land location, so the engineer can pull the right climatic data.
2. What the building is for, including whether people will work inside it.
3. Nearby structures, especially anything taller within a few building widths.
4. Door sizes and how often they’ll be open.
5. Foundation preferences or constraints, such as a lease site that can’t take concrete.

Photos of the site help. With those details, the quote you get reflects the building you’ll actually need, not a catalogue number.

Final design loads depend on site conditions, the applicable building code and project-specific engineering. This article is general information, not engineering advice for a specific structure.