The rim joist — the wooden band that sits on top of your foundation wall, where the floor joists end — is one of the most poorly insulated spots in most Ottawa homes. It's a thin piece of wood separating your basement from -30°C outside air, and it's usually 'insulated' with a fiberglass batt that does nothing to stop air movement.
Because warm air rises (stack effect), cold air gets pulled in through the rim joist and pushes warm air up and out through the attic. That's why your basement feels drafty and your floors upstairs are cold. It's also a prime entry point for humid summer air, which condenses on the cool rim joist and grows mold.
The fix is closed-cell spray foam applied directly to the rim joist. It insulates (high R-value per inch), air-seals (stops the drafts), and resists moisture (no condensation, no mold). It's a relatively small, high-impact project that most Ottawa homeowners feel the difference from immediately.
A Local Challenge We Understand
Rim joist insulation is one of the most cost-effective upgrades for Ottawa homes. Almost every home built before the 2010s in Orléans, Barrhaven, Kanata, Nepean, and Gloucester has uninsulated or fiberglass-batt rim joists that underperform in Ottawa's climate. Because the rim joist is the leakiest part of the building envelope, insulating and sealing it delivers outsized comfort and energy gains for the cost.
What You Get
The benefits our Ottawa customers see from this service.
How It Works
A clear, step-by-step process — no surprises.
Basement assessment
We inspect the rim joist for existing insulation, moisture, and mold, and confirm spray foam is the right fix.
Prep & mold check
Any moldy fiberglass is removed and the rim joist is dried and prepped; we mask off the area.
Spray foam application
Closed-cell spray foam is applied to the rim joist and sill plate, expanding to seal every gap and penetration.
Trim & verify
Excess foam is trimmed flush, and we verify the perimeter is fully sealed and insulated.
Ottawa rim joist services we provide
Searches Ottawa homeowners use to find this service — and what we deliver.
Frequently Asked Questions
Straight answers to the questions Ottawa homeowners ask us.
How much does rim joist insulation cost in Ottawa?
Rim joist spray foam in Ottawa is typically priced per linear foot and most homes range from $1,500 to $4,000 depending on basement perimeter and accessibility. It's one of the best value insulation upgrades available.
Why is the rim joist so important?
It's the thinnest, leakiest part of your home's envelope — a single wood board between your basement and the outside. Stack effect pulls cold air in through it and pushes warm air out through the attic. Sealing it stops both.
Why closed-cell spray foam and not fiberglass?
Fiberglass insulates but doesn't stop air movement, so cold air blows right through it and condenses on the cold rim joist — growing mold. Closed-cell spray foam insulates AND air-seals AND resists moisture, which is exactly what the rim joist needs.
Will insulating my rim joist help with radon?
Yes. The rim joist and sill plate are a known radon entry point. Sealing them with closed-cell foam reduces radon infiltration. For elevated radon, pair it with a mitigation system.
How long does rim joist insulation take?
Most Ottawa basements are completed in a single day. You can stay in your home during the work.