What is the minimum wall thickness for a fire-rated garage wall separating from a house in NB?

The minimum wall thickness for a fire-rated garage wall in New Brunswick is determined by the assembly required to achieve a 45-minute fire-resistance rating, not by a specific thickness requirement. The NB Building Code mandates the fire-resistance performance, and this is typically achieved with standard 2x4 or 2x6 framing plus specific drywall and insulation combinations.

Standard Fire-Rated Assembly for NB Garages

The most common fire-rated wall assembly between an attached garage and house uses 2x4 framing (3.5 inches actual thickness) with 5/8-inch Type X fire-rated drywall on the garage side. This creates a total wall thickness of approximately 4.125 inches and easily meets the required 45-minute fire-resistance rating when properly constructed with all joints taped and finished.

Many builders in New Brunswick use 2x6 framing (5.5 inches actual thickness) for the garage-to-house separation wall, which provides additional space for insulation and creates a more robust thermal barrier. This is particularly beneficial when the garage wall faces a heated living space, as it reduces heat loss and improves comfort in the adjacent room. The 2x6 assembly with 5/8-inch Type X drywall creates a wall thickness of approximately 6.125 inches.

Critical Installation Requirements

The fire-resistance rating depends entirely on proper installation, not just wall thickness. The 5/8-inch Type X drywall must be installed on the garage side with all joints properly taped, mudded, and finished — exposed joints or fastener heads compromise the fire rating. Any penetrations through the wall for electrical outlets, plumbing, or HVAC must be fire-stopped with approved sealants or fire-rated boxes. Standard electrical boxes are not acceptable in fire-rated assemblies unless specifically rated for fire separation.

The ceiling assembly above the garage requires the same 45-minute fire-resistance rating if there is living space above. This typically means 5/8-inch Type X drywall on the garage ceiling, properly supported and finished. If the garage has an attic space above with the house structure beyond, the fire separation must extend through the attic to the roof deck or to a fire-rated floor assembly above.

Insulation and Thermal Considerations

While not required for the fire rating, most NB builders include batt insulation in the fire-rated wall cavity to improve thermal performance and sound separation. Standard R-12 to R-20 batt insulation can be installed in the wall cavity without affecting the fire rating, provided the drywall installation remains compliant. This insulation significantly reduces heat loss from the house and prevents the garage wall from becoming a thermal bridge.

When to Hire a Professional

Fire separation assemblies are life-safety systems that must be installed by experienced professionals who understand the specific requirements for maintaining the fire rating. Incorrect drywall type, improper joint finishing, unsealed penetrations, or missing fire-stopping can render the assembly non-compliant and create serious safety risks. This work requires building permit approval and inspection — the building inspector will verify that the assembly meets code requirements before approving occupancy.

The door between the garage and house also requires specific fire-resistance performance — typically a solid-core door minimum 1-3/4 inches thick with self-closing hinges and proper weatherstripping to maintain the fire separation.