Is spray foam or blown-in insulation better for garage walls in Ottawa and what does each cost?

This question comes up constantly with Ottawa homeowners who want to use their garage year-round or at least keep it above freezing through winter, and the answer depends on how you use the space, how tight the building envelope is, and what you are willing to spend. Both products work in our climate but they solve different problems at very different price points.

Closed-cell spray foam is the premium option and the best-performing insulation you can put in garage walls for Ottawa's climate. It provides R-6 to R-7 per inch, so a standard 2x4 wall cavity filled with spray foam delivers roughly R-21 to R-24.5 in the 3.5-inch cavity. More importantly, closed-cell spray foam is also an air barrier and a vapour barrier in one application, which matters enormously in Ottawa where the temperature differential between inside and outside can exceed fifty degrees in January. That vapour barrier function prevents moisture from migrating through the wall assembly and condensing inside the cavity, which is a real risk in heated garages during Ottawa winters. For a standard two-car detached garage with about 600 to 800 square feet of wall area, closed-cell spray foam costs $3,500 to $6,000 installed in Ottawa. The material is applied by licensed installers using specialized equipment, and the work typically takes one day. You cannot DIY this.

Open-cell spray foam is a middle-ground option at R-3.5 to R-4 per inch, costing $2,000 to $3,500 for the same garage. It provides excellent air sealing but is not a vapour barrier, so you still need a separate poly vapour barrier on the warm side of the wall in Ottawa. Open-cell foam absorbs moisture if exposed to it, which makes the vapour barrier critical. For a heated garage in our climate, open-cell foam with proper vapour barrier is a solid performer that costs significantly less than closed-cell.

Blown-in insulation, whether cellulose or fiberglass, is the budget-friendly option. Cellulose blown into closed wall cavities costs $1.50 to $2.50 per square foot, putting the total for a two-car garage at $900 to $2,000. Blown fiberglass runs slightly less at $1.00 to $2.00 per square foot for $600 to $1,600 total. Both materials provide R-3.2 to R-3.8 per inch in wall cavities, delivering R-11 to R-13 in a 2x4 wall. The key difference from spray foam is that blown-in insulation does not seal air leaks. Every gap around electrical boxes, framing joints, and top and bottom plates allows air movement, which in Ottawa's winters means cold air infiltration and potential condensation inside the wall. You need a separate air barrier and vapour barrier, and the blown-in material needs to be dense-packed properly to prevent settling over time.

Which One Makes Sense for Your Garage

If you are heating your garage to a comfortable working temperature through Ottawa winters and using it as a workshop, home gym, or hobby space, closed-cell spray foam is worth the investment. The combined air-vapour-insulation performance in a single application eliminates the moisture risks that plague heated garages in cold climates. The higher upfront cost is offset by lower heating bills and zero risk of moisture damage inside the walls.

If your goal is simply to keep the garage above freezing to protect your car and stored items without running a heater constantly, blown-in cellulose with a proper vapour barrier is a cost-effective solution that gets you reasonable thermal performance at a fraction of the spray foam price. The R-value difference between R-13 blown-in and R-24 spray foam is significant, but for an unheated or lightly heated garage it may be more insulation than you need to achieve your goal.

One Ottawa-specific factor to consider is the garage ceiling. If you have living space above the garage, the ceiling insulation matters more than the walls, and spray foam on the ceiling is strongly recommended regardless of what you do on the walls. Heat loss upward into cold floor cavities above garages is one of the most common comfort complaints in Ottawa homes with rooms over garages.

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• 613Bins
• RenoMotion Inc.
• ALTIOR CONSTRUCTION
• Garage Door Depot-Ottawa
• ARTEXPRO Tile & Finishes