In a windy city the wall is not just a thermal barrier. It is a pressure boundary, and that changes which part of it matters.
Wind gets into walls, not just through them
Most people picture heat leaving a wall by conduction - moving slowly through insulation from warm side to cold. That happens, and it is what R-value measures.
What R-value does not describe is air being pushed into the wall cavity from outside and then out again somewhere else. In a sustained wind that is exactly what happens through any unsealed path: gaps at the sill, around window and door frames, at service penetrations, wherever the sheathing joints were never sealed.
Air moving through a cavity carries heat with it and moves straight past the insulation sitting there. This is why a wall with perfectly adequate batt can still feel cold on a windy day, and why adding depth to it disappoints.
Spray foam is used on walls in this climate specifically because it adheres to the cavity surfaces and closes those paths, rather than sitting inside them.
Where to spend first, still
Even here, the walls are rarely the first job. The attic and the rim joist are open, inspectable and cheaper, and they address the stack effect that pulls air through the house in the first place.
Do those, live with the house through a windy spell, and then decide about walls with better information. Plenty of houses stop being uncomfortable at that point.
The exposure question
If your property sits on open ground, near a coulee edge, or without a shelter belt, the wind-driven component of your heat loss is larger than the same house in a sheltered neighbourhood - and the case for sealing walls rather than merely insulating them gets stronger.
Mention your exposure when you enquire. It genuinely changes the recommendation.
Do it while they are open
The single best moment for wall work is during a renovation or a re-side, when the cavity is accessible and visible. Costs are a fraction of any retrofit approach, and the installer can confirm coverage rather than infer it.
If you are planning that work, get the envelope specified before anything closes up.
What to ask before agreeing
- What is already in this cavity?
- Which way does this wall dry, and where does the new material sit relative to any existing vapour barrier?
- Are we sealing the wall, or just filling it?
The third question is the one that matters most in Lethbridge. Filling is not sealing.
See vapour barrier and spray foam and how to fix a draughty house.
What we do
We are a referral service. We do not install. We connect you with vetted installers - certification, insurance and WCB standing checked.
No price without a site visit. Get a quote, and tell us how exposed the property is.
See also wall insulation province-wide.