Garage Insulation.
Between an attached garage and the house, Article 9.25.3.1 requires a continuous air barrier — the same clause that governs the exterior walls. The insulation is the easy half of that job.
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An attached garage is the one unconditioned space that shares walls, a ceiling and often a mechanical room with the living area. What moves through that boundary is not only heat. That is why the air separation is treated as a requirement rather than a preference.
A heated garage in Central Alberta is a small building with a very large door in it, and the door dominates the heat loss — the Zone 7A assembly figures that frame the rest of it are worth reading before deciding how far to go.
Two Different Jobs Under One Roof.
Separating an attached garage from the house and heating a detached shop are different problems with different code hooks. Most garage enquiries turn out to be one or the other, rarely both.
- The house-to-garage separation: a continuous air barrier under Article 9.25.3.1, sealed across the common wall, the ceiling below any room above, and every penetration through both.
- A room above an attached garage reads as a floor over unheated space — effective RSI 5.02 (R-28.5) in Zone 7A, unchanged whether or not there is an HRV.
- The common wall itself follows the above-ground wall requirement, effective RSI 3.08 (R-17.5) with no HRV or RSI 2.97 (R-16.9) with one, where the garage is unconditioned.
- Air sealing at the top plate of the common wall, the ceiling plane, the man door frame, and any mechanical or electrical run crossing the boundary.
- Thermal barrier handled correctly: Article 9.10.17.10 requires foamed plastic to be protected from adjacent space, with the concealed-space carve-out applying only where the assembly is genuinely closed in.
- The one garage-specific exception in the code, Sentence 9.10.17.10.(3): thermosetting foam with a flame spread rating of 200 or less in a factory-assembled storage garage door serving a single dwelling unit, foil-covered and with no air spaces.
- Foam kept 75 mm clear of any surface running above 80 °C, which in a shop with a unit heater or a flue is a real constraint rather than a formality.
- Where the garage is being heated, an honest conversation about the overhead door, since NECB puts overhead doors at 2.0 L/(s·m²) against 0.2 for a curtain wall — a scale of difference that no amount of wall insulation offsets.
Scoping a Garage.
- 01
Establish what the garage is
Unconditioned and attached, heated and attached, or a detached shop. The first is an air separation job, the second a small envelope job, the third a building in its own right.
- 02
Seal the shared boundary
Common wall, ceiling below any bonus room, and every penetration through both. This is the part that is a code requirement rather than a comfort choice, and it is usually the part that has never been done.
- 03
Decide the thermal target
A room over the garage pulls the ceiling to effective RSI 5.02. A garage being heated as workspace is a different calculation, and the overhead door will dominate it.
- 04
Settle the covering
Foam left exposed in a used garage is not in a concealed space. Interior finish, qualifying sheet metal or a listed thermal barrier — decided before spraying, not after.
Frequently Asked Questions About Garage Insulation
Does an attached garage have to be sealed from the house?
Article 9.25.3.1 requires assemblies separating conditioned space from unconditioned space to include an air barrier system providing a continuous barrier to air leakage, in both directions, and it names limiting the ingress of soil gas among its purposes. An attached garage is unconditioned space directly against conditioned space, so the wall and the ceiling between them are exactly that kind of assembly. Insulating them without sealing them satisfies neither the clause nor the reason for it.How much insulation does a room over the garage need?
It is a floor over unheated space, so effective RSI 5.02, about R-28.5, in Climate Zone 7A. That figure is identical in Table 9.36.2.6.-A and -B, so unlike walls and ceilings it does not relax when a heat recovery ventilator is installed. It is also the same number the code sets for a cathedral ceiling, which gives a sense of how much the code expects of that assembly.Is it worth insulating a garage that is not heated?
Honestly, the case is weaker than people expect. An unheated garage with an uninsulated overhead door will still track outdoor temperature closely; insulating the walls slows the swing rather than removing it. The genuinely worthwhile work in an unheated attached garage is the boundary with the house — the common wall, the ceiling, and the penetrations — because that is what affects the rooms people use. If the goal is a workshop that holds temperature, the door and a heat source come into the conversation before more wall insulation does.Can spray foam be left exposed on garage walls?
Not in an occupied garage. Article 9.10.17.10 requires foamed plastics forming part of a wall or ceiling assembly to be protected from adjacent space by an interior finish from Subsections 9.29.4 to 9.29.9, by sheet metal at least 0.38 mm thick with a melting point of at least 650 °C where the building has no Group C major occupancy, or by a thermal barrier meeting Sentence 3.1.5.15.(2). The concealed-space carve-out covers foam inside a closed wall or ceiling assembly, not foam sprayed on the face of a wall you park a vehicle against.What about the overhead door?
It is usually the dominant loss and the dominant leak. For a Part 3 building NECB 2020 allows overhead doors 2.0 L/(s·m²) of air leakage where a curtain wall gets 0.2 and an operable window gets 0.5 — an order of magnitude, written into the code because that is what overhead doors do. A house garage is not a Part 3 building, but the physics is the same, and it is why insulating the walls of a heated garage while leaving an uninsulated, unweatherstripped door tends to disappoint.