What is the best type of insulation for a New Brunswick attic? | Insulation IQ?

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New Brunswick Insulation · Accepted Answer

New Brunswick's Climate Zone 6 winters are unforgiving, and the attic is where the most heat escapes in the average NB home. Choosing the right insulation type for your attic means balancing R-value per dollar, moisture performance, installation ease, and long-term durability. For most homeowners in Moncton, Fredericton, Saint John, Miramichi, and across the province, blown-in cellulose or blown-in fibreglass are the best choices for attic insulation — and the two are closely matched enough that the right answer depends on your specific situation.

Blown-in cellulose is made from recycled paper fibre treated with borate compounds for fire and pest resistance. It delivers approximately R-3.5 to R-3.7 per inch, meaning you need about 14 inches to hit R-49 — the minimum effective thermal resistance required under the NB Building Code for new attic assemblies in Climate Zone 6. Cellulose is a dense material that fills around attic obstructions like electrical boxes, blocking, and HVAC duct supports more thoroughly than most alternatives. It has excellent air-sealing properties because the fibres pack tightly together, reducing convective heat transfer through the insulation layer. Cellulose also has a lower embodied energy than mineral wool or fibreglass, which matters to environmentally conscious homeowners. The main limitation: cellulose absorbs moisture more readily than fibreglass. In a properly detailed NB attic with a functioning vapour barrier at the ceiling plane and adequate roof ventilation, this isn't a problem. But in an attic with compromised vapour control or roof deck leaks, cellulose can retain moisture and lose R-value until dried out. Cost installed to R-49 in a 1,200 square foot attic typically runs $1,600–$2,600.

Blown-in fibreglass (loose-fill) is the other dominant choice and arguably the most common product used by insulation contractors across NB. It delivers approximately R-2.5 to R-2.9 per inch (slightly less per inch than cellulose), so you need closer to 18–20 inches to reach R-49. It's lighter than cellulose, doesn't settle as much over time (cellulose typically settles 15–20%), and is highly moisture-resistant — it won't absorb water or lose R-value when damp. For attics in older Fredericton or Saint John homes with less-than-perfect vapour barriers, fibreglass's moisture tolerance is a meaningful advantage. Cost installed to R-49 is comparable to cellulose — roughly $1,800–$3,200 for a typical NB bungalow attic, depending on existing insulation levels and air sealing scope.

Mineral wool (rock wool) batts or blown mineral wool are a premium option. Mineral wool is non-combustible, highly moisture-resistant, and delivers R-values similar to fibreglass. It's used frequently in commercial and high-performance residential projects but carries a higher material cost — typically 30–50% more than fibreglass or cellulose for equivalent coverage. For most NB attic upgrades, the performance difference over blown fibreglass or cellulose doesn't justify the premium unless fire resistance or specific acoustic performance is a priority.

Spray polyurethane foam (SPF) — specifically open-cell spray foam applied to the underside of the roof deck — creates an unvented attic assembly and provides exceptional air sealing. It's the right solution for some specific problems: homes where HVAC equipment is located in the attic (keeping it inside the thermal envelope), historical homes with complex roof geometry where venting would be difficult to maintain, or attics with chronic moisture problems tied to air leakage. Open-cell SPF delivers approximately R-3.7 per inch and must be installed to sufficient depth to maintain sheathing temperatures above the dew point in NB winters — typically a minimum of 5.5 inches. It's significantly more expensive than blown-in products (often $4,000–$7,000+ for a whole attic), so it's best reserved for cases where its specific advantages are genuinely needed.

For the majority of NB homeowners doing a standard attic top-up or starting from scratch, the decision comes down to a practical question: Is your vapour barrier sound? If yes, cellulose offers slightly better air resistance and lower cost. If uncertain, blown fibreglass's moisture tolerance makes it the safer choice. Either way, aim for R-49 minimum, R-60 if budget allows — NB Power's heating cost data shows the incremental cost of going from R-49 to R-60 is typically recovered in 4–6 additional years while protecting against future energy price increases.

Don't overlook air sealing before insulating. Sealing attic bypasses — around pot lights, partition top plates, plumbing stacks, and attic hatches — before adding blown insulation can reduce heat loss by 20–30% on its own, and most NB insulation contractors include this step in their project scope.

The insulation professionals listed on New Brunswick Insulation can evaluate your existing attic conditions and recommend the right product and depth for your hom

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