What R-value insulation do I need for addition walls in Ottawa?

Insulation is one of the most important decisions in an addition, because Ottawa's long, cold winters and warm, humid summers both test the wall assembly. The Ontario Building Code (OBC) sets the minimums, and meeting them is the starting point, not necessarily the best value for a room you'll live in for decades.

For additions, Ontario's energy efficiency rules (SB-12) give two routes: meet a compliance package, or meet the values in the addition table. For Ottawa's climate zone, the addition table calls for above-grade walls of R-19 plus R-5 continuous insulation, and a ceiling with attic space of R-60. Your designer will confirm which route your project uses and how the rest of the assembly, including the foundation and any cathedral ceilings, must be insulated.

The "continuous insulation" part matters. In a framed wall, studs interrupt the cavity insulation and conduct heat, a problem called thermal bridging. A layer of continuous rigid insulation over the sheathing, or another continuous layer, covers the studs and improves the whole wall. A common approach is a 2x6 wall with cavity insulation, mineral wool or fibreglass batts, plus exterior rigid board or semi-rigid mineral wool. Ask your designer what product and thickness meets the requirement and how windows and cladding will be detailed around it.

Spray foam is another option. Closed-cell foam adds insulation and acts as an air barrier, and at sufficient thickness it can also serve as a vapour retarder. It costs more than batts, so ask for both options priced and make sure the quote states the installed thickness and the resulting R-value.

Going beyond the minimum can make sense in a cold climate, especially for a room with several exterior walls. Ask your designer what an upgrade would cost on your specific drawings and how it changes the heat loss calculation, which also determines whether your existing heating can handle the addition.

Detailing matters as much as the numbers. In a heating-dominated climate, the vapour control layer, often polyethylene in a conventional wall, goes on the warm side of the insulation, and the air barrier must be continuous and sealed at seams, penetrations and the junction with the existing house. Poor detailing where new construction meets old is a common source of moisture problems and drafts.

Foundations and floors over unheated space need insulation as well, and your designer will specify it. When you compare quotes, ask each contractor to list the insulation type, thickness and R-value for walls, ceiling and foundation so you are comparing the same assembly. You can browse addition contractors in the Ottawa Construction Network directory and compare itemized quotes.

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

• Homeupgraders
• RenoMotion Inc.
• Diamond renovations
• Home Front Services
• Valcor Construction