Heat moves in all directions, so walls and floors must be insulated where they separate a heated space from an unheated space. This is commonly found with bonus rooms, which is where a living space is created above an attached garage.

Attached unheated garage

The walls, ceiling and door adjoining the house must be insulated and air sealed to reduce heat loss and prevent garage fumes from entering the house. Refer to Blown-in insulation, and Renovating the interior, for instructions on wall insulation if the garage is above ground, or Chapter 6, "Basement insulation," if it is below ground level.

If the garage ceiling is open and the joists are visible, proceed as outlined for open foundations (see Open foundations). It is best to remove an existing garage ceiling finish to air seal and insulate it properly.

Where a finished ceiling exists in the garage, a contractor may be able to blow dense-pack insulation into the space between it and the floor above. All holes cut in the ceiling should be carefully re-sealed to prevent any garage fumes from leaking into the rooms above, and all house ducts must be sealed with an approved sealant.

Many contractors recommend the use of professionally installed spray foam against the bottom of the floor above if there is no ceiling finish as this space is notoriously difficult to air seal. This can create a vapour barrier, an air barrier and a good initial insulating layer. Fill any remaining space with additional insulation. Any exposed spray foam will have to be covered with either drywall or approved fire-rated overspray.

If there is a ceiling finish that you do not want to remove, you can nail rigid board insulation and drywall to it as long as the surface is fairly even. Before adding the rigid board insulation, seal all potential leakage paths to prevent air from bypassing the insulation. This is especially important along any junction of the ceiling and walls where you may have to seal the cavity and spaces within the surrounding walls that typically leak into the ceiling. Seal this area with spray foam or with sections of impermeable rigid board insulation caulked between the joists (see Figure 7-11).

SAFETY WARNING:

Never run heating supply and return ducts from the house into a garage because this is dangerous and violates all codes. See "Operating your house."