What insulation suits a New Brunswick attic to stop ice dams?

Blown-in cellulose or fiberglass at R-60 is your best defence against ice dams in a New Brunswick attic — and the fix is almost always more insulation combined with better air sealing, not just adding more material on top of what's there.

Ice dams form when heat escapes through your ceiling, warms the roof deck, melts snow, and that meltwater refreezes at the cold eaves. The root cause is almost never the insulation material itself — it's insufficient depth and, critically, air leaks around pot lights, plumbing stacks, attic hatches, and partition walls that let warm interior air bypass the insulation entirely. Seal those gaps with spray foam or acoustical sealant before adding any insulation, or you're just burying the problem.

Blown-in cellulose is the most popular choice for NB attics and for good reason. It's dense enough to resist air movement, made largely from recycled newsprint, and settles to fill irregular joist bays and around obstructions better than batts. It also performs well in cold temperatures — important when Fredericton or Edmundston regularly hits -30°C. Blown-in fiberglass is a close second: lighter, won't absorb moisture if your vapour barrier has any gaps, and installs quickly. Both are well-suited to the freeze-thaw cycles NB experiences.

Spray polyurethane foam (SPF) is the premium option — it air-seals and insulates in one step, which is why it's increasingly used in new construction under NBC 2020 Tier 2 requirements (mandatory for new applications as of May 1, 2025). For an existing home, closed-cell SPF is often applied at the eaves and around penetrations, with blown-in cellulose filling the rest of the attic floor. That hybrid approach gives you the best of both worlds without the cost of foaming an entire attic.

Target R-value: NBC 2020 Tier 2 calls for approximately R-60 in attics for NB's climate zone. Many older NB homes — especially the post-war bungalows common in Moncton, Oromocto, and Riverview — were built with R-12 to R-20, which is dramatically undersized. Topping up to R-60 means roughly 16–18 inches of blown cellulose or 20+ inches of blown fiberglass.

Ventilation matters just as much as insulation. You need a clear, continuous airflow path from soffit vents to a ridge vent (or gable vents) to keep the roof deck cold and uniform. Baffles installed at every rafter bay prevent blown-in insulation from blocking the soffits. Without proper ventilation, even perfect insulation can still produce ice dams.

Cost to expect in the NB market: Air sealing plus blown-in insulation to R-60 in a typical 1,200–1,500 sq ft bungalow runs roughly $3,500–$7,000 depending on current insulation depth, attic access, and how much air sealing is needed. NB Power's Total Home Energy Savings Program offers rebates on insulation upgrades for qualifying homes — worth checking at nbpower.com before you book a contractor, as rebates can offset $500–$1,500 of the cost.

This is solidly DIY-able for the blown-in portion if you're comfortable in an attic — most rental centres carry blowing machines. However, the air sealing work around electrical boxes and plumbing penetrations requires careful attention to fire-rated materials, and if your home has knob-and-tube wiring (common in older Moncton and Fredericton homes), you cannot cover it with insulation until a licensed electrician assesses it.

Browse insulation contractors in the New Brunswick Construction Network directory to get a few local quotes — and ask each one specifically about their air sealing process, not just the insulation depth.