Quick answer: Spray foam insulates and air seals in one step, which makes it a strong choice for rim joists, cathedral ceilings, flat roofs, basement walls, crawl spaces and knee walls. Closed-cell foam gives about R-6 to R-7 per inch; open-cell gives about R-3.5 to R-3.7. For a regular open attic, blown-in insulation usually reaches R-50 for less money. Spray foam can count toward Ontario rebates, including the cathedral and flat roof attic tiers (up to $750) and bundle-path basement, wall and crawl space rebates. Amounts can change.
Updated November 2026
On this page
- 6 places spray foam makes the most sense
- How to decide if spray foam is right for you
- Spray foam and Ontario rebates
- Spray foam facts and figures
- Open-cell vs closed-cell spray foam
- Our spray foam process
- Spray foam checklist
- example project
- Framework: is spray foam worth it here?
- Frequently asked questions
- Get a free attic assessment
Pro Home Insulation installs spray foam where it solves a problem other materials cannot. We will also tell you when it is not the right tool. In most open attics, it is not.
6 places spray foam makes the most sense
- Rim joists and headers. The band of wood where your basement wall meets the floor above is one of the leakiest spots in many homes. Foam seals and insulates it in one pass.
- Cathedral ceilings. With little space between drywall and roof deck, closed-cell foam packs the most R-value into the depth you have.
- Flat and low-slope roofs. These roofs leave no room for deep loose fill, so higher R-value per inch matters.
- Basement walls. Closed-cell foam on the foundation wall adds insulation and acts as an air and vapour barrier.
- Crawl spaces. Foam on crawl space walls or the ceiling above handles damp, awkward spaces well.
- Knee walls and bonus rooms. Rooms over garages and the short walls in finished attics are often drafty, and foam seals the gaps.
How to decide if spray foam is right for you
- Check the space. If you have an open attic with room for 14 inches or more of loose fill, blown-in insulation is usually the better value.
- Look for air leaks. If the main problem is drafts at rim joists, knee walls or a room over the garage, foam is often the most direct fix.
- Measure the depth available. In a cathedral ceiling or flat roof, depth limits what you can reach. Closed-cell foam gets the most out of a shallow cavity.
- Think about moisture. Below grade, closed-cell foam is generally preferred because it resists water and slows vapour.
Our cellulose vs fiberglass vs spray foam guide goes deeper on each material.
Spray foam and Ontario rebates
Spray foam can qualify wherever the program’s R-value targets are met. Here is where it most often fits.
Standalone attic path (no energy assessment):
| Roof type and starting level | Upgrade to at least | Maximum rebate |
|---|---|---|
| Cathedral or flat roof, R-25 or less | R-28 | up to $750 |
| Cathedral or flat roof, R-12 or less | R-20 | up to $650 |
Bundle path (energy assessment plus 2 or more upgrades):
| Upgrade | Requirement | Rebate |
|---|---|---|
| Basement wall | Add more than R-22 to 100% of area | up to $1,500 |
| Basement wall | Add R-10 to R-22 | up to $900 |
| Crawl space wall | Add R-10 to R-22 to 100% of exterior wall | up to $600 |
| Crawl space ceiling | Add more than R-24 to 100% of ceiling | up to $1,200 |
| Exposed floor | Add at least R-20 | up to $300 |
| Air sealing | Meet air-change target | up to $250 |
On the bundle path you also get $600 back on the home energy assessment. Work done before the first assessment does not count, so book the assessment first. Learn more about the Home Renovation Savings Program and all current rebates.
Quick depth math (about): to reach R-28 with closed-cell foam at R-6 to R-7 per inch takes roughly 4 to 4.7 inches (28 ÷ 7 = 4; 28 ÷ 6 ≈ 4.7). With open-cell at about R-3.5 per inch, it takes about 8 inches (28 ÷ 3.5).
Spray foam facts and figures
- Air leakage accounts for about 20–30% of heat lost from an older home (Natural Resources Canada).
- A basement can account for about 20% of a home’s heat loss (Natural Resources Canada).
- Walls can account for about 20% of a home’s heat loss (Natural Resources Canada).
- One small air leak can let in 100 times more moisture than diffusion through the same area (Natural Resources Canada).
- Closed-cell foam is about R-6 to R-7 per inch; open-cell is about R-3.5 to R-3.7 per inch (general industry figures).
Open-cell vs closed-cell spray foam
| Open-cell | Closed-cell | |
|---|---|---|
| R-value per inch (about) | R-3.5 to R-3.7 | R-6 to R-7 |
| Texture | Soft, spongy | Rigid, dense |
| Air sealing | Yes | Yes |
| Vapour control | Lets vapour pass | Slows vapour |
| Water resistance | Absorbs water | Resists water |
| Good for | Interior walls, some above-grade cavities | Basements, rim joists, crawl spaces, cathedral and flat roofs |
| Relative cost | Lower per inch | Higher per inch |
Spray foam vs blown-in for an open attic: blown-in cellulose or fiberglass is usually the more cost-effective way to reach R-50 or R-60 when there is room for depth. Air sealing the attic floor first gets you much of the airtightness benefit. See our attic insulation and attic air sealing services.
Our spray foam process
- Assessment. We look at the area, measure cavity depth, check for moisture, and confirm which rebate path, if any, fits.
- Plan the R-value. You get a written quote with foam type, thickness and target R-value.
- Prep. We cover nearby surfaces, set up ventilation, and ask that people and pets stay out of the work area.
- Spray in passes. Foam is applied in layers to reach the target thickness.
- Check thickness. We measure across the area to confirm the R-value.
- Ventilate and clean up. The area is ventilated during curing, and you are told when it is fine to re-enter.
- Document. You get photos and details for your rebate file.
Spray foam checklist
- Confirm spray foam is the right fit vs blown-in or dense-pack
- Choose open-cell or closed-cell for each area
- Get the thickness and target R-value in writing
- Book your home energy assessment before work if using the bundle path
- Ask how long to stay out of the area during curing
- Clear storage away from rim joists and basement walls
- Keep photos and invoices for your rebate application
example project
example — not a specific customer.
A 1950s storey-and-a-half in Hamilton has a cathedral section over the upstairs bedroom with about R-12, plus leaky rim joists and an uninsulated basement.
- Cathedral section (standalone attic path): closed-cell foam to at least R-28 qualifies for the “R-25 or less, upgrade to R-28” tier, up to $750. Stopping at R-20 would fall in the up-to-$650 tier.
- Assumed after-tax insulation cost (for illustration, not a quote): $1,600. 50% is $1,600 × 0.5 = $800, so the rebate is capped at up to $750.
- Alternative: if the homeowner also wanted basement walls done, the bundle path could make more sense. Adding more than R-22 to 100% of the basement wall area is up to $1,500, plus $600 for the assessment. The attic rebate cannot be claimed on both paths, so the energy advisor would help choose.
Framework: is spray foam worth it here?
| Question | Points toward spray foam | Points toward another option |
|---|---|---|
| Is there room for 14+ inches of loose fill? | No | Yes: blown-in |
| Is the main problem air leaks at the edges? | Yes | No |
| Is the area below grade or damp? | Yes: closed-cell | — |
| Is it an enclosed wall cavity in an older home? | Sometimes | Often dense-pack cellulose |
| Are you doing 2 or more upgrades? | Consider bundle path | Standalone attic path |
For enclosed walls, compare with our dense-pack wall and ceiling insulation service.
Frequently asked questions
Is spray foam better than blown-in insulation?
Not always. Spray foam packs more R-value per inch and air seals as it goes, so it is strong in tight spaces. For an open attic with plenty of depth, blown-in insulation usually reaches R-50 or R-60 for less money.
What is the difference between open-cell and closed-cell foam?
Closed-cell foam is rigid, gives about R-6 to R-7 per inch, and resists water. Open-cell foam is soft, gives about R-3.5 to R-3.7 per inch, and lets vapour pass. Closed-cell is usually the choice for basements, rim joists and roofs.
Does spray foam qualify for Ontario rebates?
Yes, if the work reaches the program’s R-value targets. Cathedral and flat roof attics can qualify on the standalone attic path, and basement, crawl space and exposed floor upgrades can qualify on the bundle path. Check current rebates, because amounts can change.
Should I spray foam my rim joists?
Rim joists are a common source of drafts and cold floors in GTA basements. Closed-cell foam seals and insulates them in one step, and it pairs well with basement wall insulation.
Do I need to leave my home during spray foam installation?
You should stay out of the work area while foam is being sprayed and while it cures and the area is ventilated. We will tell you when it is fine to go back in, and the timing depends on the product and the space.
Can spray foam go in a cathedral ceiling?
Yes. Closed-cell foam is often used in cathedral ceilings because it reaches higher R-values in shallow cavities. To meet the R-28 rebate target, you need roughly 4 to 4.7 inches of closed-cell foam.
Get a free attic assessment
Pro Home Insulation brings more than 10 years of experience to spray foam and attic work across Toronto, Hamilton, Burlington and Markham. We will tell you plainly where foam pays off and where it does not. Call (647) 250-0606 or Book online.