Installation of Gypsum Board, Sheathing, and Related Substrates
This domain tests board selection, fastening, joint treatment, and the substrate conditions that make the finished assembly work. The exam links board type and thickness to the assembly's fire, moisture, and acoustic requirements.
Core rules and concepts
- Board types: regular, Type X fire-rated, moisture-resistant, abuse-resistant, ceiling board, shaftliner, and exterior gypsum sheathing. Thicknesses include 12.7 mm, 15.9 mm, and 19 mm. Type X is a listed product; not every 15.9 mm board is Type X.
- Fastening: use the correct screw type and length for wood or steel framing. Drive screws to a slight dimple without breaking the paper. Typical spacing is 300 mm (12 in.) o.c. on ceilings and 400 mm (16 in.) o.c. on walls for single-layer work, but fire-rated and ceiling assemblies often require closer spacing, so verify the listed design.
- Joints: stagger joints between layers and between opposite sides of a wall. Back-block butt joints or use control joints. Keep board off the floor and tight to the ceiling, unless a specific detail requires otherwise.
- Sheathing: orient exterior sheathing per the manufacturer, fasten on the framing, and integrate the weather barrier over it. Sheathing joints and penetrations must be sealed where they form part of the air barrier.
- Fire-rated assemblies: the listed design controls layer count, thickness, stud spacing, fastener spacing, and penetration details. Do not substitute materials.
Worked example
A plan notes a 1-hour fire separation. The listed design requires two layers of 15.9 mm Type X each side on 92 mm studs at 400 mm o.c., with joints staggered and fasteners at 200 mm o.c. at board edges. The board must be installed exactly as listed: two layers, staggered, correct screws, and no unsealed penetrations. The reasoning is that the fire rating belongs to the listed assembly, not to the board alone.
Traps that cost marks
Assuming all 15.9 mm board is Type X; aligning joints on both layers; overdriving screws and breaking the paper; using the wrong screw for steel; and fastening too close to or too far from board edges.