What is the minimum R-value required by the NB building code for above-grade walls in new residential construction, and how much does it cost to achieve that with current materials?

New Brunswick's current building code requires a minimum effective R-value of R-22 to R-28 for above-grade exterior walls in new residential construction — and the key word is effective, meaning the whole-wall performance after accounting for thermal bridging through the wood studs, not just the insulation stuffed between them.

This distinction matters enormously. A standard 2x6 wall with R-22 fibreglass batts sounds compliant on paper, but the wood studs running through that wall are only about R-6 per inch and occupy roughly 25% of the wall area. When you do the math on the whole assembly, your actual effective R-value drops to around R-16 — well below the code target. This is why the NB Building Code and the National Energy Code for Buildings both push toward continuous exterior insulation as the practical solution for achieving true code compliance.

The Standard Compliant Wall Assembly

The most common code-compliant wall system in NB new construction today is a 2x6 stud wall with R-22 mineral wool or fibreglass batts in the cavity, plus R-5 continuous rigid foam (XPS or EPS) on the exterior face of the sheathing, before the cladding goes on. This combination gets you to roughly R-24 to R-27 effective whole-wall performance, accounts for thermal bridging, and satisfies the energy compliance path under the NB Building Code. The continuous exterior layer also pushes the condensation plane outward, which is a significant moisture management benefit in NB's cold Maritime climate.

On the interior, a 6-mil polyethylene vapour barrier is installed on the warm side of the stud cavity — between the insulation and the drywall — sealed continuously with acoustical sealant at all edges and penetrations. In NB's Climate Zone 6, this vapour barrier is not optional. Without it, warm interior air migrates into the cold wall cavity, hits the cold sheathing, and condenses. You won't see the damage for years, but when you do, it's mould and rot behind your drywall.

What It Costs to Build This Wall in NB

Here's a realistic breakdown for a new 2x6 wall assembly with R-22 batts plus R-5 continuous exterior insulation in the NB market (2025-2026):

R-22 mineral wool or fibreglass batts run approximately $1.25 to $2.00 per square foot for mineral wool (Rockwool/Roxul) or $0.75 to $1.50 for fibreglass, materials only. Mineral wool is worth the premium in NB — it's dimensionally stable, hydrophobic, and performs better in the damp Maritime climate than fibreglass, which can lose R-value when it absorbs moisture.

R-5 XPS rigid foam (1 inch) on the exterior adds roughly $1.50 to $2.50 per square foot for materials. EPS is slightly less expensive at $1.25 to $2.00 per square foot and performs comparably above grade.

Installed cost for the complete above-grade wall insulation package (batts plus continuous exterior foam, including vapour barrier and labour) typically runs $4.50 to $8.00 per square foot of wall area in NB. For a 1,500 square foot bungalow with roughly 900 square feet of above-grade exterior wall, budget $4,000 to $7,200 for the wall insulation component of new construction.

A Note on Polyiso

Some builders reach for polyiso (polyisocyanurate) as the exterior continuous layer because its rated R-value of R-6 to R-6.5 per inch sounds attractive. Be cautious here — polyiso's R-value drops significantly in cold temperatures, sometimes falling to R-4 or lower when the foam gets cold. In NB winters where exterior wall temperatures regularly hit -20°C, you're not getting the R-value on the label. XPS or EPS are the better choices for exterior continuous insulation in NB's climate.

If you're building new or doing a major renovation and want to confirm your wall assembly meets current NB code, an EnerGuide evaluation by a certified energy advisor is the right starting point — and it's also required before you can access NB Power's Total Home Energy Savings Program rebates or the Canada Greener Homes Grant, which together can put $5,000 to $10,000 back in your pocket on a comprehensive energy upgrade.

Need help finding a contractor experienced with code-compliant wall assemblies in New Brunswick? New Brunswick Insulation can match you with local professionals at no cost — or browse the directory at newbrunswickconstructionnetwork.com/directory?category=insulation.