What Is Spray Foam Insulation?
Spray polyurethane foam (SPF) is a two-component insulation material that is applied as a liquid and expands rapidly to form a solid foam. It provides both thermal insulation and air sealing in a single application, which makes it particularly valuable in Renfrew County's cold climate. Unlike traditional batt or blown-in insulation, spray foam fills every gap and cavity completely, eliminating air leakage through the insulation layer itself.
There are two main types of spray foam used in residential applications: open-cell and closed-cell. Each has distinct characteristics, R-values, and best-use scenarios. Understanding the difference is essential for Renfrew County homeowners considering spray foam for their home.
Closed-Cell Spray Foam
Closed-cell spray foam is the denser and more rigid of the two types. Its cells are fully encapsulated, creating a material that is impermeable to both air and moisture. Closed-cell foam offers an R-value of R-6 to R-7 per inch, making it the highest-performing insulation material commonly used in Renfrew County homes.
Key characteristics of closed-cell spray foam:
- R-Value: R-6 to R-7 per inch
- Vapour barrier: At 2 inches thickness, it qualifies as a vapour barrier under the Ontario Building Code
- Structural strength: Adds significant rigidity to wall assemblies
- Water resistant: Closed cells do not absorb water
- Cost: $3.00 – $5.00 per board foot
In Renfrew County, closed-cell spray foam is commonly used in rim joist areas, crawlspaces, unvented roof assemblies, and basement walls. Its vapour barrier property is particularly valuable in Renfrew County's Zone 6 climate, where moisture control is critical.
Open-Cell Spray Foam
Open-cell spray foam is softer and less dense than closed-cell. Its cells are not fully encapsulated, allowing the material to expand more — up to 100 times its liquid volume — but also making it permeable to moisture vapour. Open-cell foam offers R-3.5 to R-4 per inch.
Key characteristics of open-cell spray foam:
- R-Value: R-3.5 to R-4 per inch
- Vapour barrier: No — requires separate vapour barrier in Zone 6
- Sound dampening: Excellent acoustic properties
- Cost: $1.50 – $2.50 per board foot
- Flexibility: Expands more, fills cavities completely
Open-cell spray foam is often used in interior wall cavities for sound control, in attics where a separate vapour barrier is already planned, and in applications where budget is a primary concern. However, because it requires a separate vapour barrier in Renfrew County's Zone 6, total installed cost may approach that of closed-cell when vapour barrier costs are included.
Where Spray Foam Is Used in Renfrew County Homes
Rim Joists
The rim joist area — where the floor framing meets the foundation wall — is one of the most significant air leakage points in any home. In Renfrew County, rim joists in older homes are often entirely uninsulated, allowing cold air to enter directly at the basement perimeter. Closed-cell spray foam is the preferred solution because it provides both insulation and an air seal in this hard-to-access area. Typical cost for rim joist spray foam in Renfrew County ranges from $300 to $800 depending on the linear footage.
Crawlspaces
Many Renfrew County homes, particularly seasonal cottages and older rural properties, have crawlspaces that are notoriously difficult to insulate effectively. Spray foam applied to crawlspace walls (rather than between floor joists) creates a conditioned crawlspace that protects plumbing and reduces heat loss from the floor above. Closed-cell foam is recommended for crawlspaces in Renfrew County due to the potential for ground moisture.
Attic Hatches and Access Doors
Standard pull-down attic stairs and hatch covers are massive thermal holes in a home's insulation envelope. Building an insulated box around the hatch and spraying closed-cell foam on the hatch cover itself is one of the most effective insulation upgrades for a Renfrew County home. A well-insulated attic hatch project typically costs $200 to $600.
Unvented Roof Assemblies (Cathedral Ceilings)
Cathedral ceilings and flat roofs do not have attic space for traditional insulation. In Renfrew County, closed-cell spray foam is the standard solution for unvented roof assemblies. The foam is applied directly to the underside of the roof deck, creating a conditioned attic space and eliminating the need for ventilation. This approach requires careful calculation of the R-value needed to prevent condensation on the roof deck in Renfrew County's cold climate.
Spray Foam Comparison
| Property | Closed-Cell | Open-Cell |
|---|---|---|
| R-Value per inch | R-6 to R-7 | R-3.5 to R-4 |
| Vapour barrier | Yes (2+ inches) | No |
| Cost per board foot | $3.00 – $5.00 | $1.50 – $2.50 |
| Expansion ratio | 30:1 | 100:1 |
| Water absorption | < 2% | ~ 10% |
| Best use in Renfrew County | Rim joists, crawlspaces, unvented roofs | Interior walls, noise control, budget attics |
Vapour Control with Spray Foam
Vapour control is a critical consideration for any insulation in Renfrew County's Zone 6 climate. The Ontario Building Code requires a vapour barrier on the warm side of insulation. Closed-cell spray foam, when applied at a minimum thickness of 2 inches, satisfies this requirement because the material itself is a vapour retarder.
Open-cell spray foam, however, is vapour-permeable and requires a separate vapour barrier — typically 6-mil polyethylene sheet — on the interior side. This adds cost and complexity. Some spray foam contractors recommend using closed-cell foam in any application where vapour control is a concern, which in Renfrew County's cold climate means virtually all exterior envelope applications.
An important consideration: if you are adding open-cell spray foam to an existing attic or wall cavity that already has a polyethylene vapour barrier, the combination can create a moisture trap. The vapour barrier on the warm side may prevent moisture from migrating into the foam, but if any moisture does enter, the open-cell foam will absorb it rather than allowing it to dry to the interior. This is why proper design and experienced applicators are essential for spray foam projects in Renfrew County.
Insurance Considerations
Some Renfrew County homeowners have reported that their insurance companies ask about spray foam insulation, particularly closed-cell foam applied to roof decks. While spray foam is a proven and code-compliant insulation method, a small number of insurers have expressed concerns about roof deck replacement costs if spray foam complicates access to sheathing. Always inform your home insurance provider before undertaking a major spray foam project, and check whether your policy requires disclosure of insulation upgrades.