· by Michael Blair, Nashville's Drywall Repair
Most of the drywall in a house is half-inch regular board, and a repair to it is a matter of matching the thickness and the texture. A few walls and ceilings are not regular board. They are fire-rated gypsum, usually Type X, put there because the building code requires a barrier that will hold back fire for a set time between the garage and the living space, and in some other places. A repair in those locations has to use the same board and the same detailing, or the barrier has a hole in it, and a home inspector or a Metro Codes inspector will call it.
What Type X is
Type X is gypsum board with glass fibers and other additives in the core that keep it intact longer in a fire; regular gypsum board calcines and crumbles as the water in the core is driven off, and Type X holds together and stays in place. It is made in five-eighths thickness, is a little heavier than regular board, and is labeled on the back and the edge tape. Type C is a further step, with more additives, used where a rating is needed in a ceiling assembly.
The rating belongs to the assembly, not the board: a specific thickness on specific framing with specific fasteners and joint treatment. A five-eighths Type X board on a wall with the joints taped and the fasteners at the right spacing gives the assembly a rating. The same board with open joints or a gap at the top plate does not.
Where the code wants it
The residential code requires a separation between an attached garage and the house. The common wall gets at least half-inch gypsum on the garage side, and where the garage ceiling has living space above it, the ceiling gets five-eighths Type X, along with the walls that support that ceiling. Many builders use Type X on the whole common wall as well. A door in that wall has to be a rated or solid-core door with a self-closer, and ducts through the wall have specific requirements. Metro Codes inspects to the version of the code Nashville has adopted; check with them for what applies to your house and your permit.
Elsewhere, Type X or a rated assembly shows up under stairs in some cases, in furnace and water heater closets in some configurations, in shared walls of townhouses and duplexes, and around some enclosed fireplaces. In a detached garage, the requirement is generally about proximity to the house rather than an interior wall.
- Garage side of the wall between garage and house
- Garage ceiling under living space, and its supporting walls
- Shared walls between attached units
- Some mechanical closets and under-stair spaces
Why the garage wall gets done wrong
The garage is where people hang things, run wires, add outlets and cut holes for a new door or a dryer vent, and it is the wall most often patched with whatever is in the truck. A half-inch regular patch in a five-eighths Type X ceiling, an unsealed hole where a cable went through, an attic hatch in the garage ceiling that is a piece of plywood, or a pet door in the fire door: each one is a breach in the separation. Any of them is a routine finding in a home inspection, and the fix is to restore the assembly.
The other common failure is the top of the wall. The rated wall has to be continuous to the roof deck or to a rated ceiling; a garage wall with an open gap at the top plate, or an attic that connects over the wall to the house attic without a barrier, has no separation at all regardless of what board is on it.
Repairing it correctly
A patch in a rated wall or ceiling uses the same type and thickness of board, with the cut edges backed by framing or backing strips so the patch is fastened on every side, joints taped and finished, and fasteners at the spacing the assembly calls for. Penetrations for wires, pipes and ducts get sealed with a fire-rated sealant or the appropriate collar, not ordinary caulk or expanding foam. An access hatch in a rated ceiling gets a rated hatch or is rebuilt with Type X on a proper frame.
If the wall or ceiling has been patched many times with the wrong material, the honest repair is to strip it and hang it again correctly, which in a single-car garage is not a large job. For a drywall contractor, it is a normal request. Say the wall is the garage separation and that it needs to match the rated assembly, and they will know what that means.