How to insulate a garage for cold winters

Should you insulate your garage?

It depends on how you use it. A cold garage for parking needs little, and heating it only to melt snow off the car is rarely worth the energy. A garage that holds a workshop, a home gym or a laundry area benefits from insulation and some heat. In an attached garage the case is stronger even when the garage stays cold, because the shared wall and any room above it lose heat to the cold space, and cold floors above a garage are a common complaint. The upgrade priorities guide shows where garage work sits next to attic and air-sealing jobs.

What comes first in an attached garage?

Safety and air sealing. Fumes from vehicles, fuel and chemicals must not enter the house, and fire must not travel freely between the two spaces. Building codes require an air barrier and a fire separation between the garage and the dwelling, usually with drywall and a tight, self-closing door. Seal gaps around wiring, pipes and the door frame, and keep the separation intact when adding insulation. A carbon monoxide alarm in the house near the garage wall is wise. The leak-hunting methods in air sealing a house apply directly.

Which parts of the garage should be insulated?

• Shared wall. The most important surface, with batts or other insulation, sealed drywall and a vapour control layer set out by local code.
• Ceiling under living space. Insulation here keeps the room above warm and its floor from feeling cold.
• Exterior walls. Worth doing if you will heat the garage or work in it in winter.
• Garage door. Foam kits or an insulated replacement door cut heat loss and noise, and weatherstripping around the edges stops draughts, see door weatherstripping.
• Roof or attic space. Insulate and ventilate in line with attic insulation practice.

The slab is the hardest part and is usually left alone unless you are installing a heated floor.

What materials suit a garage?

Garages see swings in temperature and humidity, and wet vehicles, so choose materials that tolerate damp. Fibreglass or mineral wool batts work in framed walls; cellulose and fibreglass are compared in our material guide. Rigid foam suits masonry walls and door panels, and spray foam seals gaps at the rim and corners. Exposed foam in a garage typically needs a code-approved covering, and the choice of covering depends on how the space is used. R-value targets vary by region, which is covered in R-values by region.

How do you heat and ventilate an insulated garage?

An insulated garage holds heat well, so a small heater may be enough. Fuel-burning heaters need proper venting and clearances, and anything gas-fired must follow code and be installed by a licensed trade. Keep some ventilation to clear fumes and moisture. If the garage later becomes living space, it will need a full envelope and heating plan.

One more use is worth a mention. At Drake Landing, the roofs of the detached garages carried the community's solar collectors, with heat sent through a buried loop to the homes, as described on the solar collection page. The same roof area is a candidate for solar panels today, so confirm structure, orientation and snow load before covering it with anything.

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