Should I use spray foam or batt insulation in my Ottawa addition walls?

The insulation in your addition walls affects heating bills, comfort and long-term durability, especially with a heating season as long as Ottawa's. Spray foam and batts can both be used to meet the energy requirements, but they perform differently in practice, and the right choice depends on the wall design and your budget.

Start with what the wall must achieve. For additions, Ontario's energy rules allow a compliance package or the addition table, which for Ottawa's climate zone calls for above-grade walls of R-19 plus R-5 continuous insulation. Your designer will confirm the route and how the cavity insulation and any continuous layer combine.

Closed-cell spray foam has a high R-value per inch, so it packs a lot of insulation into a cavity. It also acts as an air barrier, and at enough thickness it serves as a vapour retarder, which can simplify the warm side of the wall. It is the most expensive option. It should be installed by trained applicators following the manufacturer's procedures, and the space needs to be ventilated and cleared for a period after spraying, so ask about re-entry time.

Open-cell spray foam costs less than closed-cell and seals air well, but it has a lower R-value per inch and lets vapour through, so you'll usually still need a vapour control layer on the warm side. It fills irregular cavities and gaps around boxes well, which helps where a new addition ties into an older house with uneven framing.

Fibreglass batts are the most affordable option. Their weakness is air leakage: batts don't seal gaps around wiring, plumbing penetrations or framing, and poorly fitted batts lose a lot of their effectiveness. If your contractor uses batts, insist on careful fitting and thorough air sealing at plates and penetrations, plus a sealed air and vapour barrier. Adding continuous exterior insulation makes a batt wall perform much better.

Mineral wool batts cost a little more than fibreglass. They fit snugly, resist moisture and mould, keep their shape and add fire resistance. They're a good middle ground for many additions, especially paired with exterior insulation.

Whichever you choose, quality of installation matters as much as the product. Ask each contractor to list the insulation type, thickness and resulting R-value, the air sealing they include, and the vapour control approach, so you can compare quotes on the same basis. Your permit drawings need to show the assembly meets the energy requirements, and the City's Building Code Services can confirm what the submission needs. You can browse addition contractors in the Ottawa Construction Network directory and compare itemized quotes.

---

Looking for experienced contractors? The Ottawa Construction Network connects homeowners with qualified professionals:

• Justyn Rook Contracting
• JC Carpentry
• Vanguard Environmental
• Ottawa Caulking
• L.L. Renovation