Insulation Basics
Insulation basics for Canadian homes
Insulation slows the movement of heat between the inside of a home and the outdoors. In a Canadian winter that means keeping warmth in; during a humid summer it works in the other direction. The amount of resistance a material provides is described by its thermal resistance value — expressed in Canada as RSI, the metric counterpart to the imperial R-value still printed on many product labels.
Start where heat moves the most
Warm air rises, so an under-insulated attic is usually the first place worth attention. Because attic spaces are often open and accessible, adding insulation there tends to be the least disruptive improvement compared with opening finished walls.
- Attic: the most common gap in older housing and frequently the easiest to top up.
- Rim joist: the framing band above the foundation, a recurring cold spot felt on the main floor.
- Basement and foundation walls: often under-insulated in homes built before current code levels.
Choosing a material for the space
No single product fits every cavity. The decision usually comes down to how deep the space is, whether moisture is a concern, and whether the surface is open or finished.
Open attics
Blown cellulose and mineral-wool or fibreglass batts both work well in accessible attics. Blown products fill irregular spaces around joists, while batts are straightforward where framing is regular and unobstructed.
Foundations and rim joists
Rigid foam board, cut to fit and sealed at the edges, resists ground moisture better than fibrous batts in these locations.
Finished walls
Existing walls are hardest to reach. Dense-pack insulation installed from the exterior during re-siding is one approach that avoids tearing out interior finishes.
Insulation and air sealing work together
Insulation slows heat conduction, but it does not stop air leaking through gaps. The two improvements complement each other: sealing the building first, then insulating, generally produces a steadier result. The companion guide on sealing drafts covers the air-leakage side, and seasonal heating explains how to run the system once the envelope is tighter.
Before you buy
- Check the RSI marked on the packaging against the recommended level for your climate zone.
- Confirm the product suits the location — moisture-prone areas need different materials than dry attics.
- For larger projects, a registered energy advisor can measure existing levels and prioritise the work.