For a typical one- and two-family dwelling under the IRC, the “fire separation” between an attached garage and the living space is provided mainly by minimum drywall thicknesses on the garage side, protected openings, and properly treated penetrations.
Core wall and ceiling requirements
- Walls between garage and dwelling (and between garage and dwelling attic):
Not less than 1/2‑inch gypsum board or equivalent applied on the garage side. - Ceiling under habitable rooms above the garage:
Not less than 5/8‑inch Type X gypsum board or equivalent. - Structure supporting a required separation floor/ceiling assembly:
Not less than 1/2‑inch gypsum board or equivalent on the supporting members. - Exterior garage walls within 3 ft of the dwelling on the same lot:
Not less than 1/2‑inch gypsum board or equivalent on the interior side of those exterior walls.
Some jurisdictions amend this to require 5/8‑inch Type X on all dwelling‑garage separations, so local code check is critical (example: Westminster, CO adopts 5/8‑inch Type X at all separations).
Openings between garage and living space
- Door between garage and dwelling:
Must be either solid wood 1‑3/8 in minimum, solid or honeycomb-core steel 1‑3/8 in minimum, or a 20‑minute fire-rated door assembly. - No openings directly from a sleeping room into the garage.
Penetrations and ducts
- Ducts in or penetrating the separation:
Must be minimum No. 26‑gauge steel or other approved material, and must have no openings in the garage. - Other penetrations (pipes, cables, conduits, etc.):
Openings around penetrants through the required separation must be sealed with approved material to resist the free passage of flame and products of combustion, typically per IRC R302.11 item 4 (e.g., mineral wool and sealant, fireblocking foams where listed).
Typical field inspection notes
- Gypsum must be continuous, properly fastened, and finished so joints and fastener heads meet manufacturer/IRC fastening tables; large gaps, missing tape, or incomplete patching at penetrations compromise the separation.
- Any removed or cut sections for remodeling or mechanical/electrical work must be restored to equivalent fire‑resistance (same thickness and type, joints treated, penetrations sealed).
Walls perpendicular to the common wall: IRC clarifies that the “wall separation provisions of Table R302.6 shall not apply to garage walls that are perpendicular to the adjacent dwelling unit wall,” so the focus is the common separation and any parts needed to maintain continuity to the exterior.