What is the best insulation type for an older New Brunswick home?

For most older NB homes, the best insulation strategy combines closed-cell spray foam at the rim joists and basement walls, blown-in cellulose or fibre glass in the attic, and rigid foam plus air sealing in the walls — but the right answer depends heavily on your home's age, construction type, and where the worst heat loss is occurring.

Older New Brunswick homes — particularly those built before 1980 — were constructed with minimal insulation standards by today's reckoning. A typical 1960s or 1970s NB home has 2x4 framing with perhaps R-12 fibre glass batt insulation (if any was installed at all), single-pane or early double-pane windows, and an attic with R-10 to R-20 where current code calls for R-50 to R-60. The basement walls may be bare concrete or hollow block, and the rim joist area — where the floor framing meets the foundation wall — is almost always a significant source of heat loss and air infiltration.

For attic insulation, blown-in cellulose is the gold standard for older NB homes. Cellulose is made from recycled paper treated with borate-based fire retardant, and it excels at filling irregular spaces, settling around existing framing, and handling the freeze-thaw cycling NB attics experience. Blown fibre glass is also effective. The goal is achieving R-50 to R-60 in the attic — this is the single highest-impact insulation upgrade for most NB homes because heat rises and attic bypass is responsible for 25-40% of heat loss in a typical older home. Blown-in attic insulation costs $1.50-$3.00 per square foot installed, so an 800-1,000 sq ft attic runs $1,200-$3,000 — excellent return on investment.

For basement walls, fibre glass batts against a concrete or block wall are the wrong choice for NB's conditions. Without a continuous air barrier and proper vapour management, fibre glass against concrete traps moisture between the batt and the wall and creates mould conditions within a few years. Rigid foam board (XPS or polyisocyanurate) fastened directly to the concrete wall, then framed inside it, is a proven NB approach. Alternatively, closed-cell spray foam applied directly to the concrete wall provides both insulation and air/vapour barrier in one step — it is more expensive but eliminates moisture risk entirely. Closed-cell spray foam at R-6 to R-7 per inch gives you R-20 in about 3 inches and is the choice most energy advisors recommend for NB basement walls.

Rim joists — the perimeter framing just above the foundation — should be addressed with cut-and-cobble rigid foam or spray foam as a priority. These are often completely uninsulated in pre-1980 NB homes and represent a disproportionate source of heat loss and cold air infiltration relative to their size.

Wall cavities in older 2x4 homes are challenging because you cannot easily add more than R-13 to R-15 inside a finished wall cavity. The most effective approach is exterior continuous insulation during a siding replacement — adding 1.5 to 2 inches of rigid foam board under new siding adds R-7.5 to R-10 to the whole wall assembly and eliminates thermal bridging through the studs. If a full siding replacement is in your renovation plan, this is the time to add exterior continuous insulation. Costs add approximately $1.50-$3.00 per sq ft to the siding project, but the energy payback and comfort improvement are significant.

For homes built before 1980 in NB, particularly in Fredericton, Saint John, or Moncton's older neighbourhoods, get an energy audit first. A registered energy advisor will use a blower door test and thermal imaging to identify exactly where your home is losing heat — the results often surprise homeowners and redirect budget to where it will have the most impact. New Brunswick Basements at newbrunswickbasements.com has detailed guidance on basement insulation and moisture management if your project focuses on the lower level.

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

• Gionetterenovations
• Thirty Four Renovations