Spray Foam R-Value Guide for Ontario
Understanding insulation R-values and Ontario Climate Zone 6 requirements for residential and commercial buildings.
What is R-Value?
R-value measures a material's thermal resistance — its ability to resist the flow of heat. The higher the R-value, the better the material insulates. R-value is measured per inch of material thickness, and the total R-value of an assembly is the sum of all insulating layers. In Ontario, R-values are specified using the imperial system (ft²·°F·h/BTU), which is the standard used throughout the Ontario Building Code.
It is important to understand that R-value alone does not tell the full story of insulation performance. Air sealing, moisture resistance, thermal bridging, and installation quality all significantly affect how well insulation performs in real-world conditions. Spray foam insulation, because it provides both insulation and air sealing, typically outperforms its nominal R-value compared to materials that require separate air barrier systems.
R-Value Comparison Table by Material
| Insulation Material | R-Value/Inch | 3.5" (2x4) | 5.5" (2x6) | Air Barrier | Vapour Retarder |
|---|---|---|---|---|---|
| Closed-Cell Spray Foam | R-6.0 – R-7.0 | R-21 – R-24.5 | R-33 – R-38.5 | Yes | Yes (2"+) |
| Open-Cell Spray Foam | R-3.6 – R-3.8 | R-12.6 – R-13.3 | R-19.8 – R-20.9 | Yes (3.5"+) | No |
| Fiberglass Batt | R-3.1 – R-3.4 | R-12 | R-19 – R-20 | No | No |
| Fiberglass Blown-In | R-2.5 – R-3.7 | R-9 – R-13 | R-14 – R-20 | No | No |
| Cellulose (Dense-Pack) | R-3.5 – R-3.8 | R-12.3 – R-13.3 | R-19.3 – R-20.9 | Partial | No |
| Cellulose (Blown-In Attic) | R-3.2 – R-3.5 | R-11.2 – R-12.3 | R-17.6 – R-19.3 | No | No |
| Mineral Wool / Rockwool Batt | R-3.8 – R-4.2 | R-14 – R-15 | R-21 – R-23 | No | No |
| Rigid Foam (XPS) | R-5.0 | R-17.5 | R-27.5 | At seams | Yes |
| Rigid Foam (EPS) | R-3.8 – R-4.4 | R-13.3 – R-15.4 | R-20.9 – R-24.2 | At seams | Varies |
| Rigid Foam (Polyiso) | R-5.6 – R-6.5 | R-19.6 – R-22.8 | R-30.8 – R-35.8 | At seams | Yes (foil-faced) |
Ontario Climate Zone 6 Requirements
Toronto and most of southern Ontario fall within Climate Zone 6 under the Ontario Building Code (OBC) and the National Energy Code for Buildings (NECB). This zone demands high insulation standards due to approximately 3,800 heating degree days (HDD) annually. The OBC Section 9.36 and SB-12 (Supplementary Standard for Energy Efficiency) set the following minimum effective R-values:
| Building Assembly | OBC Minimum (Effective) | Recommended |
|---|---|---|
| Ceiling / Attic | R-50 (flat ceiling) / R-31 (cathedral) | R-60 |
| Above-Grade Walls | R-24 effective (nominal R-27) | R-28+ |
| Basement Walls (below grade) | R-20 (full height) | R-24 |
| Basement Slab (heated) | R-10 (edge and under) | R-10 |
| Floors over Unheated Spaces | R-31 | R-31 |
| Rim Joist / Header | R-20 | R-20 |
How Spray Foam Meets Ontario Requirements
Spray foam insulation is uniquely well-suited to meeting Ontario's demanding insulation requirements. Here is how each type addresses common applications:
Basement Walls (R-20 minimum)
Closed-cell spray foam at 3 inches provides R-20 while simultaneously serving as the vapour retarder and air barrier. This eliminates the need for polyethylene sheeting and reduces the total wall assembly thickness. Open-cell at 5.5 inches also achieves R-21, but requires a separate vapour retarder on the warm side.
Above-Grade Walls (R-24 effective)
A 2x6 wall cavity filled with closed-cell spray foam achieves R-33 to R-38.5, far exceeding the R-24 effective requirement. Even a 2x4 wall with closed-cell achieves R-21 to R-24.5. The elimination of thermal bridging and air leakage means spray foam's effective R-value is very close to its nominal rating — unlike batt insulation, where the effective value can be 15 to 30 percent lower than nominal due to installation gaps and convection.
Attic / Ceiling (R-50 minimum)
For vented attic assemblies, spray foam is applied to the ceiling plane and supplemented with blown-in insulation to reach R-50. For unvented assemblies (spray foam under the roof deck), open-cell at 12 to 14 inches achieves R-43 to R-53. Closed-cell at 4 inches (R-26) under the deck plus batt insulation below is another code-compliant approach.
Real-World Performance vs Nominal R-Value
Laboratory R-values assume perfect installation with no air movement, no moisture, and no thermal bridging. In actual Toronto homes, the effective R-value of batt insulation can be 20 to 40 percent lower than the nominal rating due to:
- Air bypass: Air flowing through and around batt insulation significantly reduces thermal performance. Studies by the National Research Council of Canada show that air leakage can reduce effective R-value by up to 50 percent in poorly sealed assemblies.
- Compression and gaps: Batts compressed around wiring, plumbing, and electrical boxes lose R-value proportionally. A 10 percent compression reduces R-value by approximately 20 percent.
- Moisture absorption: Fiberglass that absorbs even 1 percent moisture by weight can lose 30 percent of its insulating value.
- Convection within the insulation: In cold climates like Ontario's, temperature differentials across thick batt layers drive convection loops within the insulation, reducing effective performance.
Spray foam avoids all of these issues. It bonds to surfaces, fills all gaps, seals air leakage paths, and resists moisture. The effective R-value of spray foam in the field is typically 95 to 100 percent of its rated value.