What are the New Brunswick Building Code requirements for garage ventilation?

The NB Building Code requires ventilation in garages primarily to address two concerns: carbon monoxide and combustion gas management in attached garages, and moisture and air quality control in all enclosed garages, whether attached or detached. The specific requirements depend on whether the garage is attached to a dwelling, whether it is heated or insulated, and whether it contains fuel-burning appliances.

For attached garages, the most important ventilation-related code requirement is actually about air sealing — preventing garage air from migrating into the living space. The NB Building Code requires the common wall and ceiling between the garage and the dwelling to be air-sealed, and any ductwork for the home's HVAC system must not draw air from the garage space. This means no HVAC supply or return registers in the garage connected to the home's system. If you want to heat an attached garage, it needs its own independent heating system — a unit heater, infrared heater, or separate mini-split — that does not share air with the house. A carbon monoxide detector is required in the dwelling near the door to the attached garage.

Heated and insulated garages in NB have the greatest need for ventilation, and this is where many homeowners make costly mistakes. When a vehicle covered in snow and road salt enters a warm garage, the temperature differential causes rapid melting and evaporation, releasing significant moisture into the enclosed space. Without ventilation, this moisture condenses on walls, tools, ceiling surfaces, and stored items, promoting rust, mould, and deterioration. The NB Building Code and good building practice recommend either passive ventilation (vents in the gable ends or soffit-to-ridge airflow) or mechanical ventilation (an exhaust fan rated for the garage volume). A practical rule of thumb is to provide ventilation capacity that can exchange the garage air volume at least once per hour — for a standard 24x24 garage with 9-foot ceilings, that is roughly 5,200 cubic feet, requiring a fan rated at approximately 100 CFM.

Roof ventilation is required by the NB Building Code for any garage with an insulated ceiling or an attic space. The standard requirement is a 1:300 ratio of net free ventilation area to insulated ceiling area when both intake (soffit) and exhaust (ridge or gable) vents are provided, or 1:150 if only one type of vent is used. For a 24x24 garage (576 square feet of ceiling), this means roughly 2 square feet of net free ventilation split between soffit and ridge. This ventilation prevents moisture buildup in the attic space, reduces ice dam formation on the garage roof — a real concern given NB's heavy snow loads of 2.4 to 4.8 kPa — and extends the life of the roofing materials.

For detached unheated garages, the NB Building Code has minimal ventilation requirements. These structures are essentially outdoor-temperature spaces, and natural air exchange through gaps, the overhead door seals, and normal building envelope leakage provides adequate ventilation. However, if you store gasoline, solvents, paints, or other volatile materials, good practice dictates installing at least a passive vent near the ceiling to allow heavier-than-air fumes to dissipate and lighter fumes to exhaust naturally.

Garages with fuel-burning appliances — natural gas or propane unit heaters, wood stoves, or any combustion equipment — have specific combustion air requirements under the NB Building Code. The appliance needs a supply of fresh air for combustion, typically provided through a direct vent to the outdoors or through a combustion air intake duct. The sizing of this intake depends on the BTU rating of the appliance and is specified in the installation manual and the code. A licensed HVAC technician should design and install any combustion heating in a garage to ensure code compliance and safety.

From a practical standpoint, if you are building or insulating a garage in NB, plan for ventilation from the start. Adding a through-wall exhaust fan costs $200 to $500 during construction but can cost $800 to $1,500 to retrofit after the walls are insulated and finished. A timer switch or humidistat-controlled fan is ideal — it runs automatically when moisture levels rise and shuts off when the air is dry, saving energy without requiring you to remember to turn it on. Need help planning your garage ventilation system? Get matched with a local garage contractor through New Brunswick Garages for a free estimate.