Hanging
Garage drywall: the fire-separation rules and type X
An attached garage is the one place most houses need fire-rated drywall. The rules are short and specific, and they decide which board goes on which surface.
Why garages are different
A garage holds cars, fuel, solvents and lawn equipment, and garage fires spread to the house through the shared wall and the ceiling. The International Residential Code answers with a simple separation: gypsum board on the garage side of every surface between the garage and the house. It is not a rated assembly; it is a prescriptive minimum that slows a fire long enough to get out.
The rules in Table R302.6
| Separation | Minimum on the garage side |
|---|---|
| Garage from the house and its attic | 1/2 in gypsum board or equivalent |
| Garage from habitable rooms above | 5/8 in type X gypsum board or equivalent |
| Structure supporting that floor-ceiling assembly | 1/2 in gypsum board or equivalent |
| Garages within 3 ft of a dwelling on the same lot | 1/2 in board on the interior side of the exterior walls in that area |
In plain terms: the wall the garage shares with the house gets at least 1/2 in board. If there is a bedroom or bonus room over the garage, the garage ceiling gets 5/8 in type X, and any walls or beams holding up that ceiling get at least 1/2 in. A garage with only an attic above needs 1/2 in on the ceiling, if the attic is open to the house. Local amendments can be stricter, and many builders hang type X on the shared wall too.
The sound and fire assemblies table lists these rules alongside the rated assemblies they are often confused with.
The door and the ducts
The separation is only as good as its openings. The IRC (R302.5) sets three rules:
- No opening into a sleeping room. A door from the garage cannot open directly into a bedroom.
- The door between garage and house must be solid wood or solid- or honeycomb-core steel at least 1-3/8 in thick, or a 20-minute fire-rated door. Recent code editions also require it to be self-closing and self-latching; check the edition your jurisdiction uses.
- Ducts passing through the separation must be at least 26 gauge sheet steel, with no openings into the garage.
Penetrations for pipes and wires through the board are sealed with approved material, usually a fire-rated sealant.
Counting the board
A 24 × 24 ft attached garage, 9 ft walls, two overhead doors, one house door, one window
- House wall: 24 × 9 − 20 = 196 sq ft, 7 sheets of 1/2 in (or type X)
- Other walls: 507 sq ft after openings, 18 sheets of 1/2 in
- Ceiling on trusses 24 in apart: 576 sq ft, 20 sheets of 5/8 in, or sag-resistant 1/2 in
- 45 sheets of 4 × 8 in all, 1,200 screws, 2 pails of compound and 2 rolls of tape for a Level 2 finish
With a bonus room above, the same 20 ceiling sheets must be 5/8 in type X, and every joint and screw head is taped and covered even if the garage is never painted. The garage drywall calculator splits the order by surface and board.
The ceiling choice comes from the trusses as much as from fire: garage trusses are usually 24 in apart, where regular 1/2 in board sags. The thickness selector and the drywall thickness guide explain the limits.
How far the finish has to go
Fire separation does not need a painted finish, but it does need the joints closed. Taping the joints and covering the fastener heads, a Level 1 or Level 2 finish, keeps fire and smoke from finding the seams. Most garages get Level 2: tape embedded with a thin coat over it, and one coat on the screws, which is what GA-214 recommends for garages. If the garage will be painted and used as a workshop, Level 3 under a texture or Level 4 under paint. The finish level selector and the guide to levels of drywall finish help decide.
Common questions
Do the other garage walls need drywall? Not under the separation rule, unless the garage is within 3 ft of the house on the same lot. Most owners board them anyway for a clean, insulated workspace.
Is type X needed on the shared wall? The IRC asks for 1/2 in. Some jurisdictions, and some builders, use 5/8 in type X there as a matter of course. Ask your building department.
What about the attic hatch? An attic access in a garage ceiling that is part of the separation needs a cover that keeps the separation: typically a hatch of the same board, or a listed attic ladder assembly. Check the code edition you build under.
Can I leave the garage ceiling open? Only if nothing above it connects to the house. Where the attic over the garage is open to the house attic, the ceiling is part of the separation.
A one-hour wall is a different thing
The garage separation is not a fire rating. A one-hour wall, needed between units in a two-family dwelling or in some commercial work, is a specific tested assembly: for example the Gypsum Association’s WP 3660, one layer of 5/8 in type X on each side of 2 × 6 studs, with screws at 7 in. The fire-rated drywall calculator counts those assemblies, and the guide to fire-rated assemblies explains the difference.
Common mistakes
- 1/2 in regular on a garage ceiling under a bedroom. It must be 5/8 in type X.
- Leaving joints untaped. The separation needs closed seams.
- An ordinary hollow-core door to the house. Not allowed.
- Plastic ducts or registers into the garage. Not allowed.
- Forgetting the walls that hold up the room above. They need board too.