What R-value insulation do I need in garage walls for a heated garage in Fredericton NB?

For a heated garage in Fredericton, you should insulate the walls to a minimum of R-20, with R-24 being the recommended target for comfortable year-round use as a workshop or hobby space. Fredericton experiences roughly 4,800 to 5,000 heating degree days per year with winter temperatures regularly reaching -25 to -30 degrees Celsius, so under-insulating a heated garage means high energy bills, uncomfortable working conditions, and wasted money on heating fuel.

The most common and cost-effective approach for garage wall insulation in NB is fibreglass batt insulation in 2x6 framing. A 2x6 wall gives you a full 5.5 inches of cavity depth, which accommodates R-20 batts perfectly and can accept R-22 high-density batts for a modest cost increase. If your garage is framed with 2x4 walls (3.5-inch cavity), you are limited to R-12 or R-14 batts, which is inadequate for a heated garage in Fredericton's climate. In that case, you can add rigid foam board insulation to the interior or exterior of the wall to boost the total R-value — a 1.5-inch layer of extruded polystyrene (XPS) rigid foam (R-7.5) over the 2x4 wall brings the assembly to approximately R-20.

For a heated garage, the vapour barrier is just as important as the insulation itself. Install a 6-mil polyethylene vapour barrier on the warm (interior) side of the insulation, overlapping seams by at least 6 inches and sealing all penetrations, joints, and edges with acoustic sealant or red tuck tape. In Fredericton's cold climate, warm moist air from inside the heated garage will try to migrate through the wall toward the cold exterior. Without a proper vapour barrier, that moisture condenses inside the wall cavity, soaking the insulation (which destroys its R-value) and eventually rotting the framing. This is one of the most common failures in heated NB garages — the insulation was installed but the vapour barrier was skipped or poorly sealed.

Ceiling insulation is equally critical and often more important than the walls because heat rises. For a heated garage with an unfinished attic above, insulate to R-32 minimum, and preferably R-40 to R-50. Blown-in cellulose or fibreglass over the ceiling joists is the most economical method for this, costing $2 to $4 per square foot installed in the Fredericton area. If your garage has a finished bonus room or loft above, the ceiling insulation requirements change — you will need to insulate the knee walls and roof slope of the room above rather than the garage ceiling.

Do not forget the garage door itself in your insulation plan. An uninsulated garage door is the single largest thermal hole in the building. For a heated garage in Fredericton, you need an insulated door with an R-value of at least R-12, and preferably R-16 or higher. Replacing a non-insulated door with an insulated one typically costs $1,200 to $3,500 installed depending on size, but the energy savings and comfort improvement are dramatic. If replacement is not in the budget, a DIY insulation kit with polystyrene panels ($50 to $150) provides some improvement, though it will not match a factory-insulated door's performance.

The garage slab is another area of heat loss that is often overlooked. If the slab is already poured, you can install rigid foam insulation vertically along the interior perimeter of the foundation wall (from the top of the slab down to the footing level), covered with a durable finish material to protect it from impact. This reduces heat loss through the slab edge, which is the primary path for thermal energy to escape from a slab-on-grade garage.

For materials and installed costs in the Fredericton area, expect to pay $1.50 to $3.00 per square foot for fibreglass batt insulation in walls (installed, including vapour barrier) and $3.50 to $7.00 per square foot for closed-cell spray foam, which provides air sealing and vapour barrier in one application. A complete insulation package for a 24x24 two-car garage — walls, ceiling, and vapour barrier — typically runs $2,500 to $5,000 installed with batts, or $5,000 to $10,000 with spray foam.

This is a project where professional installation is worth the investment, particularly for the vapour barrier detailing and ceiling insulation. Poorly installed vapour barriers cause more problems than no vapour barrier at all in some cases. Get matched with insulation contractors through New Brunswick Garages for free estimates on your project.