Should I use faced or unfaced batt insulation in my New Brunswick attic? | Insulation IQ?

For the vast majority of New Brunswick attics, the correct choice is unfaced batt insulation — and understanding why comes down to how vapour control works in a vented attic assembly.

In a typical vented residential attic in NB, the vapour retarder belongs at the ceiling plane, not up in the attic floor insulation itself. The standard approach is to apply a 6-mil polyethylene vapour barrier (or use drywall taped and sealed as a vapour retarder in newer construction) at the warm-in-winter side of the assembly — the ceiling of your living space below. The insulation then sits on top of that barrier, filling the joist bays and extending well above the joists in a cross-layer arrangement to minimise thermal bridging.

Faced batts have a kraft paper or foil facing that acts as a vapour retarder. When you install faced batts in an attic floor with a polyethylene sheet already below them, you're creating a potential double vapour barrier — trapping any moisture that enters from either direction with nowhere to go. This is a recognised moisture problem in cold climates like Climate Zone 6, where New Brunswick sits, and can lead to mould, rot, and degraded insulation performance over time.

Unfaced batts allow moisture that gets into the insulation assembly to dry toward the vented attic space above, which is exactly the drying direction you want. The already-installed poly or taped drywall ceiling below handles vapour control.

There is one scenario where faced batts make sense in an attic: if you are insulating between rafters in a cathedral ceiling or unvented roof assembly and the facing is being used as the primary vapour retarder without a separate poly layer, and the product and assembly are explicitly designed for that purpose. This is a more specialised situation and should be reviewed against NBC 2020 provisions for unvented roof assemblies — if you're in doubt, consult a building science professional.

For a standard vented attic in a Moncton bungalow, a Saint John two-storey, or a Fredericton raised ranch, the correct specification is straightforward:

• Install a continuous 6-mil poly vapour barrier at the ceiling plane (or verify the existing one is intact and properly lapped and sealed at all seams and penetrations).
• Lay unfaced batts to fill the joist cavities to full depth, typically R-20 (RSI 3.52) to start.
• Cross-layer with additional unfaced batts or blown-in insulation perpendicular to the joists until you reach the NB Building Code minimum of R-50 (RSI 8.8) for attics in Climate Zone 6 (required in new construction; strongly recommended in retrofits).
• Maintain proper ventilation channels at the eaves — baffles (also called rafter baffles or wind baffles) keep the soffit-to-ridge airflow path open and prevent moisture-laden attic air from accumulating.

In terms of cost, unfaced fibreglass batts for an attic floor run roughly $0.25 to $0.50 per square foot for materials, depending on R-value and brand. If you're topping up an existing attic to R-50 from R-20, blown-in cellulose or fibreglass (added over existing unfaced batts or existing insulation) is often a faster and more economical option than laying additional batt layers — blown-in runs approximately $0.80 to $1.50 per square foot installed.

Before doing attic insulation work in New Brunswick, it is worth contacting NB Power's Home Energy Efficiency Program and checking whether your project qualifies for the Canada Greener Homes Grant. Both programs can offset costs significantly for attic upgrades, but the Greener Homes program requires a pre- and post-retrofit EnerGuide evaluation by a registered energy advisor, so planning ahead saves money.

If you're uncertain about the existing vapour barrier condition or want a professional assessment of your attic assembly, New Brunswick Insulation contractors listed on the New Brunswick Construction Network can provide an on-site evaluation and accurate quote.

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

• Brunswick insulation & roofing
• Gionetterenovations
• Arctic Fox Construction Inc.
• Thirty Four Renovations
• 3Tone Construction Ltd

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