Medicine Hat gets more sunshine than almost anywhere in Canada, and a garage is the building on your property least equipped to deal with it.
The summer half nobody plans for
Most garage insulation conversations are about winter. Here, summer earns equal billing.
A garage typically has a large roof area, a big uninsulated door, and minimal shading. Through a long sunny afternoon that roof deck absorbs heat and radiates it downward into the space. If you are working in there, that is the difference between a usable workshop and somewhere you leave by two o'clock.
It matters more if the garage is attached. A hot garage on a shared wall pushes heat into the house all afternoon, exactly when the house is already working hardest to stay cool.
A continuous sealed layer works in both directions - it slows heat leaving in January and slows it arriving in July. If you are insulating a garage here, count the summer benefit rather than treating it as incidental.
Attached: deal with the shared assemblies
If the garage is attached, the priority is not the garage's exterior walls. It is the surfaces it shares with heated space:
- The common wall between garage and house.
- The garage ceiling, if there is living space above it. That room is almost always the least comfortable in the house, sitting over an unheated space with framing that leaks air on several sides. See bonus room insulation.
There is a safety dimension too. That boundary is a fire separation and the barrier that keeps vehicle exhaust and fuel vapour out of the living space. Sealing it properly is worth doing on those grounds alone, and it happens to be the same work that fixes the comfort problem.
Detached: decide what you want first
A detached garage is a standalone building, so the only question is what you want from it.
Heating it to work in means sealing matters more than depth, because a detached garage is usually built loosely - single-layer sheathing, unsealed penetrations, and a large door that empties the space every time it is used. The achievable goal is a building that warms quickly and holds it between openings.
Leaving it unheated means insulation will do very little. An unheated garage with no heat source sits near outside temperature regardless of what is in the walls. Insulation slows heat movement; it does not create heat. We would rather say that than take the job.
The covering requirement
Foam in a garage needs an appropriate thermal barrier over it, and a garage is exactly where that gets skipped because the space feels like a utility building. Get it specified in the quote. See thermal barrier vs ignition barrier.
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 say whether the garage is attached, and whether you intend to heat it.
See also garage spray foam insulation province-wide.