Door From Garage to House: Fire Separation Code (IRC)

The door from a garage into a house must be 1⅜ in solid wood or steel, or a 20-minute fire-rated door, with a self-closing device in the model code, and there can be no door at all from the garage into a bedroom. Around it, the garage has to be separated from the house by at least ½ in gypsum board on the garage side of the walls and ceiling it shares with the house, upgraded to 5/8 in Type X where a habitable room is above the garage. Ducts and other penetrations have their own rules. This post walks through 2021 IRC R302.5 and R302.6 (the same section numbers in the 2024 edition) on a real ranch plan.

Table R302.6: what gets drywall

Three details trip people up. The ½ in board goes on the garage side of the shared walls. Where the house's attic runs over the garage, the garage ceiling (or the wall between the garage attic and the house attic) needs the board too, because the rule says *residence and attics*. And where a bedroom or bonus room sits over the garage, the ceiling becomes 5/8 in Type X, and the walls and beams that hold that ceiling up need at least ½ in board as well. The separation provisions do not apply to garage walls that are perpendicular to the adjacent dwelling wall.

The door between the garage and the house

Openings and penetrations are in R302.5. The door rule is R302.5.1:

• No opening from the garage directly into a room used for sleeping. You cannot enter a bedroom from the garage, even through a rated door.
• Other openings need a solid wood door at least 1⅜ in thick, a solid or honeycomb-core steel door at least 1⅜ in thick, or a 20-minute fire-rated door.
• The door must have a self-closing or automatic-closing device in the model code. Several states amend this requirement out, so check your local edition before you buy hinges.

Hollow-core interior doors, the usual 1⅜ in bedroom door, do not qualify. A steel exterior door, or a solid-core wood door, is the usual choice, and many builders use one with weatherstripping and a threshold because the garage slab sits lower than the house floor.

Ducts and other penetrations

• Ducts in the garage, and ducts passing through the walls or ceiling between the garage and the house, must be at least No. 26 gage sheet steel or other approved material and must have no openings into the garage (R302.5.2). No supply or return grille in the garage from the house system.
• Other penetrations of the separation, such as pipes, wires and boxes, are protected as required by R302.11, item 4: the gap around them is filled with an approved material that resists the free passage of flame and products of combustion (R302.5.3).
• Attic access from the garage into a shared attic should keep the membrane intact; ask the building department what hatch they accept.

Two neighbouring rules complete the garage: the floor must be an approved noncombustible material, and the parking area must slope to a drain or toward the vehicle door (2021 IRC R309.1, now R317 in 2024). Carbon monoxide alarms are generally required in a house with an attached garage that opens into it (2021 R315; R311 in 2024).

The separation on a ranch plan

FloorGen's 3-bed ranch with 2-car garage template has a 22 × 24 ft garage on the wall grid (507 ft² net) at the west end of a single-storey house, with a 16 ft vehicle opening facing the street. The garage shares its east wall with the entry and a short stretch of the kitchen, and its back wall with the laundry / mudroom and the dining room. No bedroom touches it, and the only door into the house is a 32 in door into the laundry / mudroom.

The door into a mudroom rather than the kitchen or a hall is a good arrangement anyway: it gives a place to drop boots and bags, and it keeps the self-closing door off a main route. If you ever convert the garage to living space, the rules change; see garage conversion floor plans.

What FloorGen checks

FloorGen's IRC profile checks room sizes, stairs, guards and door swings. It does not check fire separation, door ratings or ducts: draw the plan, then note the separation walls and the door on it for your permit set (see how to draw floor plans for a permit). The rules above are the 2021 model code; states amend them, and this is not legal advice.