What are the NB Building Code requirements for vapour barriers when air sealing a Caraquet home?

New Brunswick Building Code requires a vapour barrier with a permeance rating of 60 nanograms or less (typically 6-mil polyethylene) on the warm side of all insulated assemblies in exterior walls, ceilings, and floors over unheated spaces. For a Caraquet home in northern NB's harsh coastal climate, proper vapour barrier installation is absolutely critical to prevent moisture damage that can destroy wall assemblies within just a few years.

Vapour Barrier Placement and Installation Standards

The vapour barrier must be installed on the interior (warm) side of the insulation in all exterior wall and ceiling assemblies. In NB's Climate Zone 6, this means the polyethylene goes against the interior face of the wall studs, under the drywall. The Code requires continuous coverage with all seams overlapped by at least 150mm (6 inches) and sealed with acoustical sealant or approved tape. Every penetration through the vapour barrier — electrical boxes, plumbing stacks, pot lights, HVAC ducts — must be sealed with acoustical sealant, gaskets, or approved sealing methods.

For Caraquet specifically, the coastal location brings additional moisture challenges from Bay of Chaleur humidity and persistent winds that drive moisture into building assemblies. The vapour barrier becomes even more critical because any gaps allow warm, moist interior air to reach cold surfaces within the wall cavity, where it condenses into liquid water. In northern NB's extended heating season (October through April), this moisture accumulation can cause mould growth and wood rot that remains hidden behind walls until structural damage occurs.

Air Barrier vs Vapour Barrier Requirements

While the vapour barrier controls moisture movement, the NB Building Code also requires an air barrier system to control air leakage. New construction must achieve 3.2 ACH50 (air changes per hour at 50 pascals) or better. The 6-mil polyethylene vapour barrier can serve as both vapour barrier and air barrier when properly installed with continuous sealing. However, achieving true air tightness requires sealing the vapour barrier to the foundation sill plate, around window and door rough openings, at all electrical and plumbing penetrations, and at the ceiling-to-wall junction.

Coastal Caraquet Considerations

Caraquet's location on the Acadian Peninsula means homes face salt air, driving rain, and temperature swings that stress building envelopes. The vapour barrier installation must be perfect because coastal moisture can approach the wall assembly from both sides — interior humidity from daily living and exterior moisture from weather events. Smart vapour retarders (variable permeance membranes like MemBrain) are increasingly popular in coastal NB renovations because they allow walls to dry inward during summer while still blocking vapour drive during the heating season.

Common Code Violations to Avoid

Never install vapour barriers on both sides of a wall assembly — this traps moisture and guarantees rot. Don't use kraft-faced batts as a vapour barrier in NB; the kraft facing has insufficient vapour resistance for our climate. Avoid puncturing the vapour barrier with staples or nails any more than necessary, and seal every penetration. The attic hatch, which many contractors ignore, must have weatherstripping and an insulated cover that maintains vapour barrier continuity.

When to Hire a Professional

Vapour barrier installation requires experience with proper sealing techniques, understanding of building science, and knowledge of how different assemblies connect. A poorly installed vapour barrier is worse than no vapour barrier because it gives false confidence while allowing hidden moisture damage. Professional installers understand the critical details — sealing to electrical boxes with acoustical sealant, maintaining continuity at corners and intersections, and integrating the vapour barrier with window and door installations.

For your Caraquet project, consider having a blower door test performed both before and after the air sealing work to verify Code compliance and identify any remaining leakage points. This testing is also required for NB Power rebate eligibility if you're upgrading insulation as part of the project.