The numbers, explained
Spray Foam R-Value Guide for Ontario Buildings
Closed cell spray foam gives roughly R-6 per inch and open cell gives roughly R-3.6 per inch, so 2 inches of closed cell is about R-12 and a 2x6 wall full of open cell is about R-20. Those are the numbers most people are looking for when they search. The rest of this guide explains where they come from, what Ontario's building code expects and how many inches you need for common targets.
R-value measures how well a material resists heat flowing through it. It's a useful way to compare insulation, but it's only part of the story, because R-value is tested without air moving through the material. In a real house, air leaks carry heat around and through insulation, which is why a lower R-value that also air seals can outperform a higher one that doesn't, especially in older homes with lots of small gaps.
The certified installers at Super Sprayers work with these numbers every day across Guelph and the surrounding region. We always confirm targets against the compliance package, the building permit or the rebate requirements for your specific project, because the right number for a new home, a renovation and a rebate claim can all be different.
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R-Value per Inch: Open vs Closed Cell
| Thickness | Closed cell (about R-6 per in) | Open cell (about R-3.6 per in) |
|---|---|---|
| 1 in | R-6 | R-3.6 |
| 2 in | R-12 | R-7 |
| 3 in | R-18 | R-11 |
| 3.5 in (2x4 cavity) | R-21 | R-13 |
| 5.5 in (2x6 cavity) | R-33 | R-20 |
Values are approximate. Each product publishes its own tested long-term R-value.
What Ontario Code Requires
New houses in Ontario follow Supplementary Standard SB-12. These are typical prescriptive values for most of southern Ontario, including Guelph. Verify against the SB-12 edition referenced by the 2024 Ontario Building Code and your compliance package.
| Building element | Typical prescriptive target |
|---|---|
| Ceiling with attic space | R-60 |
| Ceiling without attic space | R-31 |
| Exposed floor | R-31 |
| Above-grade walls | R-22 or equivalent |
| Basement walls | R-20 continuous or R-12 plus R-10 continuous |
| Heated slab or slab under 600 mm below grade | R-10 |
Performance-path designs can trade values between components. Your energy advisor or designer sets the targets for a new build.
How Many Inches for Each R-Value Target
| Target | Closed cell | Open cell | Blown cellulose |
|---|---|---|---|
| R-20 | About 3.3 in | About 5.6 in | About 5.5 in |
| R-24 | About 4 in | About 6.7 in | About 6.5 in |
| R-31 | About 5.2 in | About 8.6 in | About 8.5 in |
| R-60 | About 10 in | About 16.7 in | About 16 to 17 in |
R-60 in foam is rarely practical, which is why attics usually reach it with blown-in insulation over an air-sealed floor.
Aged R-Value and Why It Matters
Closed cell foam's R-value comes partly from the blowing agent trapped in its cells. Over years, a little of that gas is replaced by air, and the R-value settles to a lower, stable level. That settled number is the long-term thermal resistance, or LTTR, tested under CAN/ULC-S770.
When comparing products, look at the LTTR, not the fresh value. The figures on this page are aged values.
Why Air Sealing Beats Raw R-Value
An R-40 attic with open top plates and leaky pot lights can lose more heat than an R-30 attic that's properly sealed. Warm air carries heat straight past insulation it doesn't have to go through. It also carries moisture that condenses in the attic.
That's why we always air seal first, and why spray foam's air sealing is worth as much as its R-value. See our air sealing page.
Getting an Attic to R-60
For a vented attic, the practical route is to seal the floor with spray foam, then blow in 16 to 17 inches of cellulose or about 20 to 22 inches of fiberglass. For an unvented attic with the foam at the roofline, the design has to keep the sheathing warm, usually with thick closed cell alone or foam plus another insulation. Our attic insulation page covers both.
R-Value Questions
What R-value do 2 inches of closed cell give?
About R-12, depending on the product's tested long-term R-value.
What R-value does an Ontario attic need?
SB-12 calls for about R-60 in an attic for new homes, and rebate programs use their own starting and finished targets.
Related Services and Guides
- Closed Cell Spray Foam The highest R-value per inch, with vapour control built in.
- Attic Insulation Fewer ice dams and upstairs rooms that hold heat.
- Open Cell vs Closed Cell Which foam belongs where, and why.
- Ontario Building Code and Spray Foam Thermal barriers, vapour barriers, permits and standards.
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