Heat loss in Canadian homes
A heated house is constantly losing warmth to the outside. Two mechanisms dominate in a cold climate: heat conducted through solid surfaces, and warm air escaping through gaps while cold air is drawn in to replace it.
Two ways heat leaves
Conduction is heat moving through a material — through drywall, framing, glass, and the insulation between studs. Air leakage, sometimes called infiltration, is the bulk movement of air through unsealed joints, penetrations, and gaps. The two are separate problems with separate fixes: insulation slows conduction, while air sealing addresses leakage.
This distinction matters because insulation alone does not stop drafts. A wall can hold a thick batt and still feel cold near an unsealed electrical box or where the wall meets the floor, because air is moving past the insulation rather than being slowed by it.
RSI and R-value. Resistance to conductive heat flow is expressed as RSI in metric units and R-value in imperial units. A higher number indicates more resistance. The two scales describe the same property, so insulation sold in Canada is often labelled with both.
Common weak points, roughly top to bottom
In a typical detached house, certain locations recur as places where heat escapes. The list below moves from the top of the building envelope downward.
| Location | Primary mechanism | Typical note |
|---|---|---|
| Attic hatch and ceiling plane | Conduction + leakage | Large flat area; warm air rises toward it. |
| Recessed lights, plumbing stacks | Air leakage | Penetrations through the ceiling plane. |
| Exterior walls | Conduction | Largest continuous surface of the envelope. |
| Window and door frames | Conduction + leakage | Glass conducts; the rough opening can leak. |
| Rim joist (where floor meets foundation) | Air leakage | Often under-insulated and hard to reach. |
| Basement walls and slab edge | Conduction | In contact with surrounding ground. |
Why the attic and walls come first
The ceiling plane and exterior walls are large, continuous surfaces. Because they cover so much area, work there generally affects more total heat flow than a fix applied to a small, isolated spot. Warm air also rises, which concentrates pressure differences near the top of the house and makes the attic boundary an early priority in many assessments.
How leakage is observed
Air leakage is not always visible. Two common approaches are used to find it:
- Blower-door testing depressurises the house with a fan so that leaks become easier to feel and locate.
- Thermal imaging can reveal temperature differences on surfaces, which sometimes correspond to missing insulation or moving air.
Both are diagnostic. They describe where a house is losing heat rather than fixing it, and results depend on conditions at the time of the test.
A note on numbers. The share of heat lost through any one surface varies widely between houses depending on age, construction, and condition. Rather than quoting a single figure, it is more reliable to have a specific house assessed.