Ask a homeowner where their house loses heat and they'll say windows or the attic. Energy audits across Ontario keep pointing somewhere else: the rim joist — the band of wood sitting on top of your foundation where the floor framing meets the outside wall.
Why Rim Joists Leak
The rim joist is a maze of framing intersections, sill plates, and penetrations for wiring, plumbing, and vents — none of it built to be airtight. It sits right at the top of the foundation where wind pressure is constant. In most houses it's insulated (if at all) with a scrap of fibreglass stuffed between joists, which does nothing to stop air movement.
That's why your floors are cold, why the basement feels drafty, and why the furnace runs longer than it should. Cold air enters low at the rim, warm air exits high — the stack effect running through your house all winter.
The One-Visit Fix
Two inches of closed-cell foam sprayed into each rim joist bay seals every crack and gap while insulating to about R-12 with a built-in vapour barrier. Fibreglass can't do this — it filters air rather than stopping it, and it collects condensation against the cold rim. Foam stops the air, stops the moisture, and never sags or degrades.
For most homes in our Essex County service area this is a half-day visit — and it's the highest-impact insulation work you can buy for the space involved. Get a quote and we'll bundle it with basement walls if you're finishing the space.