Closed Cell vs Open Cell Spray Foam in Ontario

Both closed-cell and open-cell spray foam are excellent insulation materials, but they serve different purposes. For Ontario homeowners, choosing the right type depends on where you are insulating, your moisture exposure, your R-value requirements under the Ontario Building Code, and your budget. This guide provides a thorough comparison tailored specifically to Ontario's Climate Zone 6 conditions.

Understanding the Fundamental Difference

The core distinction between closed-cell and open-cell spray foam lies in their cellular structure. Closed-cell foam has cells that are completely sealed and filled with a blowing agent gas that provides high thermal resistance. The result is a dense, rigid material with high R-value per inch and excellent moisture resistance. Open-cell foam has cells that are not completely closed, creating a softer, more flexible material that allows some moisture vapour to pass through. It uses water as its blowing agent and expands dramatically during installation.

Side-by-Side Comparison

Ontario Building Code Requirements by Application

The OBC specifies minimum R-value requirements that determine which foam type and thickness you need. Here is how each foam type meets the code for common applications in Climate Zone 6 (Toronto and most of southern Ontario):

Basement Walls (OBC Minimum R-20)

Closed-cell at 3 inches achieves R-20 on its own, with the added benefit of acting as a vapour retarder. This is the industry-standard approach for Toronto basements because it addresses both insulation and moisture management in a single application. Alternatively, 2 inches of closed-cell (R-13) can be combined with R-8 batt insulation to achieve code compliance at slightly lower cost.

Open-cell at 5.5 inches achieves approximately R-21, meeting code requirements. However, open-cell requires a separate vapour retarder (usually latex vapour-retarder paint or 6-mil polyethylene) when used on below-grade walls. For basements with any history of moisture intrusion, closed-cell is strongly recommended.

Above-Grade Walls (OBC Minimum R-24 effective)

In 2x6 framing, closed-cell at 3 inches (R-20) combined with exterior continuous insulation is the premium approach. For interior-only applications, open-cell filling the full 5.5-inch cavity (R-21) is cost-effective but may need exterior insulation to reach the effective R-24 target.

Attic / Roof Assemblies (OBC Minimum R-50 for ceiling)

For unvented roof assemblies (spray foam under the roof deck), the OBC requires air-impermeable insulation. Open-cell at 10 to 12 inches provides R-38 to R-46, typically needing supplemental insulation to reach R-50. Closed-cell at 4 inches (R-26) under the roof deck with additional batt insulation is another approach, though the cost is significantly higher.

Rim Joists (No specific OBC minimum, but R-20 recommended)

Rim joists are one of the most important areas to insulate and seal. Closed-cell at 2 to 3 inches is the standard recommendation because rim joists are exposed to exterior temperatures and prone to condensation. Closed-cell provides insulation, air sealing, and vapour retardance in a single application at this critical junction.

Cost Analysis for Ontario Homeowners

To achieve equivalent thermal performance, the cost difference between closed-cell and open-cell is smaller than per-square-foot prices suggest. For example, to achieve R-20 in a basement:

• Closed-cell (3"): $3.50 to $5.50 per sq ft, but no additional vapour barrier or supplemental insulation needed.
• Open-cell (5.5"): $2.00 to $3.50 per sq ft, plus $0.50 to $1.00 per sq ft for vapour retarder application.

When you factor in the vapour retarder requirement, the effective cost gap narrows to approximately 20 to 30 percent. For below-grade and moisture-prone applications, the insurance value of closed-cell's moisture resistance often justifies the remaining premium.

Moisture Performance in Ontario's Climate

Ontario's climate creates challenging moisture dynamics. In winter, warm interior air carries moisture toward cold exterior surfaces. In summer, humid outdoor air can drive moisture inward through the building envelope. The dew point regularly falls within the wall cavity during the heating season.

Closed-cell foam prevents moisture from reaching cold surfaces and eliminates condensation within the wall cavity. At 2 inches or more, it acts as a Class II vapour retarder, controlling moisture flow without a separate poly sheet. This is particularly important in Toronto basements where concrete walls wick ground moisture and create high humidity conditions.

Open-cell foam is vapour-permeable, meaning moisture can pass through it. In heating-dominant climates like Ontario's, this can be an advantage when paired with a proper vapour retarder on the warm side, as it allows the wall assembly to dry toward the interior if needed. However, without proper vapour control, open-cell foam in basements can lead to moisture accumulation behind the foam.

Our Recommendation for Toronto Homeowners

For most Toronto homes, we recommend a hybrid approach: closed-cell spray foam in the basement, rim joists, and any moisture-prone areas, and open-cell spray foam in attics and above-grade walls where budget optimization makes sense. This strategy maximizes performance where it matters most while keeping total project costs reasonable.