Flat roofs and Kootenay snow load: what 73 winters taught us
Every winter since 1953 our crews have watched what Kootenay snow does to flat roofs, not in a lab, but on flat roofs across Trail and the West Kootenays. Here is what all that winter taught us, in plain terms.
A flat roof is built for snow
A sound flat roof is not a gamble against winter. The deck is sized to carry the load, the surface slopes toward the drains, and the membrane keeps the water out while the snow sits there. Plenty of the commercial buildings in downtown Trail wear a flat roof, and they have worn one through every winter we can remember.
The trouble starts when one of those three parts is compromised: a deck that has been soaked and weakened, drains that are plugged, or a membrane past its best. Winter does not create those problems. It finds them.
What winter actually does to a flat roof
The snow itself mostly just sits there. The damage comes from water in its other forms.
- Freeze-thaw at the seams. Meltwater works into any loose edge, freezes at night, and pries. A seam that would hold for years in a dry climate opens fast here.
- Ice at the drains. Drains are the low, cold spot. If they ice over, the melt behind them ponds. Ponding water finds every weak point on the roof.
- Spring melt. The hardest test is not the cold snap. It is the warm week when a winter’s worth of snow turns to water at once and the drains have to move all of it.
The membrane matters less than the details
We install torch-on, TPO and PVC, and each has its winter strengths: two-ply torch-on takes shovel traffic without complaint, and welded TPO and PVC seams hold through freeze-thaw because they are fused, not glued. But the system on the roll matters less than the drains, the flashings and the edges. That is where a flat roof wins or loses a winter.
What you can do before the snow flies
- Get the drains cleared in the fall. Leaves and grit from summer plug them right when you need them most.
- Look things over after the first big dump and after every thaw, from a window or a ladder at the eave. You do not need to walk the roof.
- Take phone photos of anything that changes: a sag, a new stain inside, water sitting where it never sits in summer.
- If snow has to come off, talk to us before anyone goes up. Shovels and ice chippers wreck more membranes than the snow itself.
If water is coming in now
See our emergency roof repair page. It covers what to do while you wait and what we do when we arrive. Move what you can out from under the drip, catch the water, and stay off the roof.
Common questions
Usually not. A sound flat roof in the Kootenays is built to carry a normal winter's snow. The time to act is a heavy, wet, late-season dump on a roof with known trouble. Trail Roofing would rather look first, because clearing snow blind does more membrane damage than most storms.
The snow itself mostly sits there. The damage comes from water: freeze-thaw prying at seams, ice building at the drains, and ponding when spring melt outruns the drainage. In the Kootenays the fall drain check Trail Roofing recommends prevents most of it, and it is the first thing we look at.