What is the NB energy code requirement for continuous insulation on exterior walls? | Insulation IQ?

The New Brunswick Building Code, aligned with the National Energy Code for Buildings (NECB) 2015 and the Part 9 prescriptive path for residential construction, requires that exterior wall assemblies in Climate Zone 6 achieve a minimum effective thermal resistance of RSI 3.08 (approximately R-17.5). However, the critical term here is effective — and this is where continuous insulation plays a central role in meeting that standard.

A standard 2x6 wood-frame wall filled with fibreglass batts has a nominal cavity insulation value of about R-22, but the effective R-value of the assembly is significantly lower — typically around R-15 to R-16 — because wood framing members conduct heat at a much faster rate than insulation. This thermal bridging through the studs, plates, and headers can reduce the wall assembly's thermal performance by 20 to 30 percent. To compensate, the NB code and energy pathway increasingly rely on continuous insulation (CI) applied to the exterior side of the sheathing, where it wraps the framing without interruption and eliminates the thermal bridging penalty.

For a 2x6 wall with batt insulation plus exterior CI, the typical code-compliant approach in NB involves one of the following combinations: R-19 or R-22 batts plus RSI 1.25 (R-7.1) of exterior rigid foam, or R-20 batts plus a 1.5-inch layer of extruded polystyrene (XPS) or polyisocyanurate board on the exterior. XPS delivers approximately R-5 per inch, while polyisocyanurate offers R-6 to R-6.5 per inch at ambient temperatures (though its effective R-value drops in very cold conditions, a consideration for NB winters). Mineral wool (rock wool) rigid board is also increasingly used for continuous insulation in NB because it is vapour-open, fire-resistant, and performs consistently across temperature ranges.

The vapour management implications of adding exterior CI are significant and must be understood before specifying the CI thickness. In Climate Zone 6, the vapour barrier (polyethylene sheet) is placed on the warm-in-winter side of the insulation — typically behind the interior drywall. When exterior CI is added, the sheathing (OSB or plywood) moves to a warmer position in the wall assembly because the CI keeps it above the dew point for a greater portion of the year. This is thermodynamically favourable and reduces the risk of condensation within the wall. However, if the exterior CI is too thin relative to the cavity insulation, the sheathing can still reach dew-point temperatures in severe cold — a concern NB Building Code Section 9.25 addresses through condensation control requirements.

The prescriptive tables in Part 9 of the NB Building Code allow builders to choose between several wall assembly options without detailed energy modelling. These options include:

• 2x6 studs at 400mm O.C. + R-22 batt + RSI 1.25 CI (approximately R-7 exterior foam)
• 2x6 studs + R-19 batt + RSI 1.76 CI (approximately R-10 exterior foam)
• Advanced framing (600mm O.C.) + R-22 batt + RSI 0.88 CI (approximately R-5 exterior foam)

For new construction targeting Step Code or Net Zero Ready performance — increasingly common in Fredericton, Moncton, and Saint John projects pursuing energy certifications — exterior CI requirements are substantially higher, often R-15 to R-20 or more on the exterior, combined with advanced framing and high-performance windows.

For retrofits on existing homes, the most practical way to add continuous insulation is during a re-siding project. Stripping old cladding, adding 1.5 to 2 inches of rigid foam over the existing sheathing, re-furring the wall with vertical strapping, and installing new cladding over that strapping is a well-established approach in NB. This kind of retrofit qualifies for both NB Power Home Energy Savings Program rebates and the Canada Greener Homes Grant, which can offset a meaningful portion of the material cost.

Building permit applications for new construction in NB must include wall assembly specifications that demonstrate code compliance, and the insulation inspection will verify that the specified CI thickness and type has actually been installed. If you're designing a wall assembly for a new build or major retrofit and want to confirm it meets the NB energy code requirements, the insulation professionals on New Brunswick Insulation can help you specify the right combination of cavity and continuous insulation for your project.

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