What's the best insulation for basement walls in New Brunswick's climate?

For New Brunswick basements, rigid foam insulation on the interior side of foundation walls is typically your best bet, providing excellent moisture control and thermal performance in our challenging climate.

Polyisocyanurate (polyiso) rigid foam boards are the top choice for most NB basements. At 2-3 inches thick, they deliver R-12 to R-18 while creating a continuous thermal barrier that prevents condensation on cold concrete walls. The foil facing acts as a vapor barrier, which is crucial given our high humidity levels and frequent freeze-thaw cycles. Expect to pay $3-5 per square foot for materials, with professional installation adding $8-12 per square foot.

Extruded polystyrene (XPS) is another excellent option, particularly for below-grade applications. It handles moisture better than expanded polystyrene and won't lose R-value if it gets damp. At 2 inches thick, XPS provides about R-10 and costs slightly less than polyiso.

New Brunswick's climate creates unique basement challenges that make insulation choice critical. Our deep frost line (4+ feet), spring flooding risks along the Saint John River system, and clay soils with high water tables mean basement walls face both exterior moisture pressure and interior condensation issues. Many older NB homes - especially those 1970s-1990s split-levels common in Riverview, Quispamsis, and suburban Moncton - have chronic basement moisture problems that proper insulation can help address.

Installation requires careful attention to code compliance. Under the National Building Code 2020 (effective May 1, 2025 for new applications in NB), finished basements need proper vapor barriers, fire-rated assemblies, and adequate egress windows. If you're creating living space, you'll need a building permit from your municipality (like Moncton Planning & Development at 856-4375) or your Regional Service Commission if you're in a rural area.

The professional vs. DIY decision depends on your scope. Installing rigid foam boards is manageable for experienced DIYers, but electrical work (moving outlets, adding circuits) requires a licensed electrician with proper NB Power permits (1-800-615-0522). If you're finishing the entire basement, hiring a contractor ensures proper fire separation, egress compliance, and integration with your heating system.

Start by testing for radon - New Brunswick has some of Canada's highest radon levels, with about 1 in 4 homes exceeding Health Canada guidelines. A long-term test kit ($30-50) will tell you if you need mitigation before insulating. Address any moisture issues first, then consider upgrading your heating system - many NB homes still rely on oil furnaces that struggle to heat finished basements efficiently.

Find verified basement finishing contractors in our New Brunswick directory who understand local moisture challenges and code requirements.