Garage Drywall Calculator

What the code requires

Table R302.6 of the 2024 International Residential Code sets four separation requirements for an attached garage:

• From the dwelling unit and attics: not less than 1/2 in gypsum board or equivalent, applied to the garage side. This covers walls shared with the house and a ceiling with only attic above.
• From portions of the dwelling unit above the garage: not less than 5/8 in type X gypsum board or equivalent. This is the ceiling under a bonus room or any other part of the house.
• Structure supporting floor/ceiling assemblies used for that separation: not less than 1/2 in gypsum board or equivalent. In practice, the garage walls that hold up the room above.
• Garages less than 3 ft from a dwelling unit on the same lot: not less than 1/2 in gypsum board on the interior side of exterior walls within that area.

The 2024 edition widened the type X trigger. The 2021 table said habitable rooms above the garage; 2024 says portions of the dwelling unit above the garage, so a storage room or bathroom above now counts too. Garage walls perpendicular to the house wall are not covered by the wall rows.

Many jurisdictions amend the IRC, and some require type X on every garage surface. Treat this calculator as the model-code minimum and confirm with your building department before you order.

Hanging the type X ceiling

Table R702.3.5 sets the fastening for 5/8 in type X at a garage ceiling beneath habitable rooms: applied perpendicular to the framing, framing no more than 24 in on center, and fasteners every 6 in, using 1-7/8 in galvanized nails or equivalent drywall screws. That is a tighter schedule than an ordinary ceiling, so buy screws accordingly.

Ask your inspector how the joints must be treated. Many expect at least a coat of compound over tape on every joint and fastener of a separation, even in a garage that will never be painted.

The door into the house

Section R302.5.1 covers the door the drywall surrounds. It must be solid wood or solid or honeycomb-core steel at least 1-3/8 in thick, or a 20-minute fire-rated door, and it must be self-latching with a self-closing or automatic-closing device. No opening is allowed from the garage directly into a bedroom.