Attic Insulation Guide — Hawkesbury & Renfrew County, Ontario

Why Attic Insulation Is Critical in Eastern Ontario

The attic is the single most important area to insulate in any home, and this is especially true in Hawkesbury and the surrounding Renfrew County area. Heat rises, and in a typical uninsulated or under-insulated attic, up to 25% of a home's heat loss occurs through the roof. In Hawkesbury's climate — with winter temperatures regularly dropping below -25°C — proper attic insulation directly affects heating costs, comfort, and the structural integrity of the roof system.

Homes across Renfrew County and Prescott-Russell were built over many decades, each era with different insulation standards. Many pre-1970 homes in Hawkesbury have attics with minimal or no insulation. Even homes built in the 1980s and 1990s may only have R-20 to R-30 in the attic, far below current recommendations for Climate Zone 6. Upgrading attic insulation to R-60 is one of the most cost-effective energy improvements a property owner can make in eastern Ontario.

Attic Insulation Types

Blown-In Cellulose

Blown-in cellulose is one of the most popular attic insulation choices in Renfrew County. Made from recycled paper products treated with fire retardants, cellulose is blown into the attic using a hose, filling irregular spaces and covering obstructions like electrical wires, plumbing vents, and ductwork. Cellulose has an R-value of approximately R-3.5 to R-3.8 per inch.

Cellulose settles slightly after installation, so contractors typically overfill by about 5–10% to achieve the target R-value. It has good sound-dampening properties and is treated to resist mould and pests. In eastern Ontario's humid conditions, cellulose performs well when properly installed with adequate attic ventilation.

Blown-In Fibreglass

Blown-in fibreglass is another common attic insulation option. It is lighter than cellulose and does not settle as much, making R-value calculations more predictable. Fibreglass has an R-value of approximately R-2.2 to R-2.5 per inch, meaning more depth is needed to achieve R-60 compared to cellulose. A typical R-60 installation requires approximately 22–26 inches of blown-in fibreglass.

Fibreglass is non-combustible and does not absorb moisture like cellulose. However, it does not fill gaps as effectively as cellulose, so air sealing before installation is even more critical when using blown-in fibreglass in Hawkesbury homes.

Fibreglass Batts

Fibreglass batt insulation is commonly used for new construction attics where roof framing is exposed and accessible. Batts are pre-cut rolls that fit between joists. They are less common for attic retrofits because existing attics have obstructions that make proper batt installation difficult. Batts have an R-value of approximately R-3.0 to R-3.3 per inch.

Proper installation of batts requires careful cutting around obstructions and ensuring no gaps or compression. In Renfrew County, batt insulation in attics is more common for new builds than retrofits, where blown-in insulation is generally preferred.

R-Value Targets for Climate Zone 6

Hawkesbury and all of Renfrew County fall within Ontario Climate Zone 6, the coldest zone in southern Ontario under SB-12. This classification requires higher attic insulation levels than most of the province. The Ontario Building Code minimum for attic insulation in Zone 6 is R-50, but energy efficiency professionals widely recommend R-60 for optimal performance.

R-60 corresponds to approximately 18–22 inches of blown-in cellulose or 22–26 inches of blown-in fibreglass. Achieving this level in an existing attic may require raising the attic floor level or adding joist extensions (sistering) if the current joist depth is insufficient to hold the insulation. This is a common consideration in older Hawkesbury homes where attic joists may only be 6–8 inches deep.

For new construction, the Ontario Building Code requires compliance with SB-12, which mandates R-60 for ceiling assemblies in Climate Zone 6. This is a significant increase from the R-40 that was common in older building codes.

Ventilation Baffles

Proper attic ventilation is essential for any insulation installation in Hawkesbury's climate. Ventilation baffles (also called rafter vents) are plastic or foam channels installed between rafters to maintain an airflow pathway from the soffit vents to the ridge vent or gable vents. Without baffles, blown-in insulation can block soffit vents, trapping moisture in the attic.

In eastern Ontario, where winter humidity from the Ottawa River valley contributes to higher indoor moisture levels, proper attic ventilation prevents condensation on the underside of the roof deck. This condensation can lead to mould growth, rot, and ice dams. Baffles are a small cost item (typically $2–$5 each) but are critical for long-term attic performance.

Air Sealing Before Insulating

In Climate Zone 6, air sealing the attic before adding insulation is arguably more important than the insulation itself. Air leaks bypass the insulation entirely, allowing warm, moist air from the house to enter the attic. In Hawkesbury's cold winters, this causes several problems:

• Ice dams from snow melting on warm roof areas and refreezing at the eaves
• Frost accumulation on attic surfaces that melts and causes moisture damage
• Significant heat loss that reduces the effectiveness of even R-60 insulation
• Increased risk of mould and rot in attic framing

Common air sealing points in Hawkesbury homes include: attic hatches, plumbing vent stacks, electrical wire penetrations, chimney chases, recessed lighting fixtures, and top plates of interior walls. Each of these should be sealed with caulk or spray foam before insulation is installed. Our air sealing and vapour barrier guide covers this process in detail.

Existing Construction vs. New Construction

Attic insulation approaches differ significantly between existing homes and new construction in Renfrew County. In existing homes, blown-in insulation is the standard choice because it can be installed without removing the attic floor. The insulation is blown through a hose from outside, covering existing insulation and filling all cavities. A careful contractor will assess the existing insulation condition, identify any moisture problems, and perform air sealing before adding new material.

In new construction, attics are typically insulated with blown-in fibreglass or batts after the ceiling drywall is installed. The full air sealing of the ceiling plane is completed before insulation, and baffles are installed during framing. New construction also allows for proper installation of attic access hatches with insulation and weatherstripping.

Cost Estimates for Attic Insulation

For a typical 1,000 square foot attic in Hawkesbury, the cost to upgrade to R-60 using blown-in cellulose typically ranges from $2,500 to $5,500 including air sealing, baffle installation, and labour. The wide range reflects differences in access difficulty, existing insulation removal, and current material prices.

For a more detailed breakdown of all insulation costs in Renfrew County, see our complete cost guide.

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