How do I insulate the floor of a room built above an Ottawa garage?

The floor of a room built above a garage separates heated living space from a space that can be close to outdoor temperature in an Ottawa winter. Get it wrong and you end up with cold floors, high heating bills and possible moisture problems inside the floor cavity. Getting it right comes down to four things: insulation, continuous insulation to reduce thermal bridging, vapour control and air sealing. Your designer will specify the exact assembly and the insulation level the Building Code requires for it, so use the points below to understand what they draw and to ask good questions.

Insulation. The joist cavities are filled with insulation, and many designers add a continuous layer of rigid insulation as well. The continuous layer matters because wood joists conduct heat, and a layer that runs across them reduces that loss. Mineral wool is often chosen for this location because it handles moisture well and resists fire; fibreglass costs less. Ask your contractor to price both and explain what they recommend.

The garage ceiling. The ceiling below the room is also part of the separation between garage and living space, which has its own Code requirements to keep out car exhaust and slow the spread of fire. Your designer will specify the drywall and how joints and penetrations are sealed.

Vapour control. In a cold climate, the warm side of the insulation, here the upper side toward the heated room, needs vapour control so warm, moist indoor air doesn't reach cold surfaces and condense. The assembly should be designed so it can still dry if some moisture gets in. Avoid trapping the cavity between two vapour-tight layers; ask your designer to confirm how the assembly is meant to dry.

Air sealing. This often matters as much as the insulation level. Every penetration through the floor, such as wiring, pipes and ducts, should be sealed, and the rim joist where the floor framing meets the outside walls is a well-known leakage point. Spray foam or careful membrane and sealant work are common ways to deal with it.

Heating also plays a role. A room over a garage loses heat from more sides than an ordinary bedroom, so ask your HVAC contractor for a heat-loss calculation to size the heating, and consider whether a floor-level heat source makes sense.

Ask contractors to itemize the floor insulation, ceiling, vapour control and air sealing so you can compare quotes. You can browse addition contractors in the Ottawa Construction Network directory at justynrookcontracting.com and compare quotes.

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Looking for experienced contractors? The Ottawa Construction Network connects homeowners with qualified professionals:

• 613Bins
• RenoMotion Inc.
• ALTIOR CONSTRUCTION
• Pure Flow Water Solutions inc.
• Demontigny Carpentry