Chapter 3 of 532% of exam
Installation and Repair
Installation and Repair is the largest C-9 section at about 32%: ceilings, standard walls, fire-rated and specialty assemblies, trims and repairs. This page is a short survey; the PrepPass C-9 Drywall study guide teaches the code tables, calculated ratings and repair methods in depth.
Ceilings and walls
Ceiling fasteners are closer than wall fasteners, and wider framing needs perpendicular board.
Wet texture on ceilings
Perpendicular application; 1/2 in at 16 in o.c., 5/8 in (or 1/2 in sag-resistant) at 24 in o.c.
2025 CRC §R702.3.5Screws
Into wood: Type W or S, 5/8 in penetration; thin steel: Type S, 3/8 in.
2025 CRC §R702.3.5.1Fire-rated work
Rated assemblies are tested systems; joints and fasteners are treated and penetrations are protected.
Boxes in rated walls
Steel boxes up to 16 sq in; 100 sq in per 100 sq ft; 1/8 in maximum gap.
2025 CBC §714.4.2Garage under rooms
5/8-inch Type X ceiling.
2025 CRC Table R302.6Wet areas and repairs
Tubs and showers need listed backers; repairs restore the surface and any rating.
Water-resistant board
Not over a vapor retarder in tub or shower compartments, nor where directly wet.
2025 CBC §2509.3