Spray Foam Insulation Guide — Smiths Falls & Renfrew County

Open-Cell vs. Closed-Cell Spray Foam

Spray polyurethane foam (SPF) insulation comes in two main types, and choosing the right one for your Smiths Falls home depends on where it will be applied and what you need it to do.

Open-Cell Spray Foam

Open-cell spray foam is a low-density foam (typically 0.5 lb/ft³) that expands to fill cavities and provides R-3.6 to R-4.0 per inch of thickness. It is semi-rigid and acts as an air barrier but not as a vapour barrier under Ontario's Building Code. Open-cell foam is best suited for interior wall cavities and attic applications where a separate vapour barrier will be installed. It is more cost-effective than closed-cell at $2.50 to $5.00 per board foot.

An important consideration for Smiths Falls homeowners: open-cell foam absorbs and holds moisture if it comes into contact with liquid water. It should not be used in basements with flood risk or in direct ground contact. However, it excels at sound dampening — a useful property in multi-unit homes and townhouses common in Smiths Falls.

Closed-Cell Spray Foam

Closed-cell spray foam is a high-density foam (typically 2.0 lb/ft³) that provides R-6.0 to R-7.0 per inch — nearly double the R-value per inch of open-cell. It is rigid when cured and acts as both an air barrier and a vapour barrier, which means it can replace the need for a separate polyethylene vapour barrier in most applications. Closed-cell foam costs $4.00 to $8.00 per board foot, making it significantly more expensive than open-cell.

Closed-cell foam is ideal for rim joists in Smiths Falls homes — those exposed bands at the basement ceiling where the floor system meets the foundation. These are among the leakiest areas in a house and a major source of heat loss. A single 2-inch layer of closed-cell foam on rim joists effectively seals and insulates this area. Closed-cell is also the right choice for crawlspace walls, cathedral ceilings (where cavity depth is limited), and attic hatches.

Where Spray Foam Excels in Smiths Falls Homes

The older building stock common in Smiths Falls — century homes along Beckwith Street, heritage homes near the Rideau Canal, and post-war bungalows — presents specific challenges that spray foam can address effectively.

Rim Joist Insulation

Rim joists (the band joist between the foundation wall and the first floor) are a major source of heat loss in almost every Smiths Falls home. These areas are often uninsulated or poorly insulated and leak air directly to the exterior. Closed-cell spray foam applied to a depth of 2–3 inches seals and insulates rim joists in one step. Cost for a typical 1,500 sq ft home: $600 to $1,200 for rim joist spray foam.

Crawlspace Walls

Smiths Falls homes with crawlspaces — common in houses with stone foundations along the Rideau Canal corridor — benefit enormously from closed-cell spray foam on crawlspace walls. The foam seals the space against moisture and provides the air sealing that is essential in the humid Rideau Valley climate. A typical crawlspace job ranges from $3,000 to $7,000 depending on size and access.

Cathedral Ceilings

Cathedral and vaulted ceilings leave limited cavity depth for insulation. In a 2x8 rafter (7.25-inch cavity), open-cell foam provides less than R-28 — well below the R-40 required by code. Using closed-cell foam at R-6.5 per inch, a 7.25-inch cavity reaches approximately R-47, meeting code with room to spare.

Attic Hatches and Access Doors

The attic hatch is one of the most commonly overlooked insulation points. A poorly insulated attic hatch can undo much of the benefit of an R-60 attic. Spray foam applied to the back of an attic hatch, combined with weatherstripping, creates an effective thermal and air seal.

Vapour Control Properties of Spray Foam

Under Ontario's Building Code, a vapour barrier is required on the warm-in-winter side of insulation in Climate Zone 6. For open-cell spray foam, a separate polyethylene vapour barrier must still be installed, typically on the interior face of the foam. For closed-cell spray foam applied to a minimum thickness of 2 inches (approximately R-12+), the foam itself serves as the vapour barrier, and no additional polyethylene layer is needed.

This distinction matters in Smiths Falls older homes where wall cavities may be irregular, making it difficult to install polyethylene sheets neatly. Closed-cell spray foam in these situations provides both insulation and vapour control in a single application that conforms to irregular surfaces.

Fire Safety Considerations

Spray foam insulation must be covered with a thermal barrier when installed in occupied spaces under the Ontario Building Code. Typically this means a ½-inch layer of drywall over the foam. In attics and crawlspaces that are not habitable spaces, an ignition barrier may be required instead. Always verify fire code requirements with your local building department before installing spray foam.

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