Every interior wall and ceiling in a modern American home starts as a sheet of panel material screwed to the framing. Wallboard is the general term for these panels, with standard drywall (gypsum board) being by far the most common type. But drywall is just one option. Moisture-resistant green board, mold-resistant purple board, cement backer board, and fire-rated Type X all serve specialized purposes that standard drywall cannot handle. Choosing the right wallboard for each room prevents moisture damage, meets building code, and saves money on repairs down the road.
Standard Drywall (White Board)
Regular drywall consists of a gypsum plaster core sandwiched between two sheets of paper facing. It comes in 4×8-foot sheets as the standard size, with 4×10 and 4×12 available for rooms with taller ceilings or fewer horizontal seams. Common thicknesses include:
- 1/4 inch: Used for curving around arches and covering existing damaged walls. Too thin for structural attachment to framing.
- 3/8 inch: Occasionally used in repairs and remodeling over existing surfaces. Not code-compliant as a single-layer wall covering in most jurisdictions.
- 1/2 inch: The standard thickness for walls and ceilings with framing spaced 16 inches on center. A 4×8 sheet costs $10-$15 at home improvement stores.
- 5/8 inch: Required for ceilings with 24-inch joist spacing to prevent sagging, and often required on garage walls and ceilings adjacent to living spaces for fire resistance.
Moisture-Resistant Wallboard (Green Board)
Green board uses a water-resistant paper facing and a wax-treated gypsum core to resist humidity better than standard drywall. It was the go-to choice for bathrooms and kitchens for decades, though it has been largely superseded by newer products. Green board costs $13-$18 per 4×8 sheet, roughly 30-50% more than standard drywall.
Important limitation: green board resists moisture but is not waterproof. It should never be used inside a shower or tub surround where direct water contact is expected. For those applications, cement board or a waterproof panel system is required.
Mold-Resistant Wallboard (Purple Board)
Brands like Gold Bond and Georgia-Pacific produce mold-resistant panels with fiberglass mats instead of paper facing and antimicrobial additives in the gypsum core. These panels outperform green board in high-humidity environments because mold feeds on paper, and fiberglass-faced panels eliminate that food source. A 4×8 sheet costs $15-$22.
Use mold-resistant wallboard in bathrooms, laundry rooms, basements, and any room where humidity regularly exceeds 60%. It is worth the modest price premium over standard drywall in these spaces because replacing moldy drywall costs far more than the upfront difference.
Cement Board
Cement board, sold under brands like Durock, Hardiebacker, and Wonderboard, is a rigid panel made of Portland cement and reinforcing fibers. It is completely waterproof and serves as the substrate for tile in showers, tub surrounds, and kitchen backsplashes. Standard sizes are 3×5 feet in 1/4-inch and 1/2-inch thickness.
Cement board costs $10-$15 per 3×5 sheet. It is heavier and harder to cut than drywall, requiring a scoring knife or a carbide-tipped circular saw blade. All seams must be taped with alkali-resistant mesh tape and thinset mortar before tiling.
Fire-Rated Wallboard (Type X)
Type X drywall contains glass fibers mixed into the gypsum core that slow heat transfer during a fire. A single layer of 5/8-inch Type X provides a 1-hour fire rating, meeting the code requirement for walls between a garage and living space, furnace rooms, and certain commercial applications.
Type X costs $13-$18 per 4×8 sheet in 5/8-inch thickness. Double-layer Type X assemblies achieve 2-hour fire ratings required in some multi-family and commercial buildings. Your local building code determines where fire-rated wallboard is mandatory, so check before purchasing standard drywall for a renovation.
Installation Basics
Wallboard installation follows the same general process regardless of type:
- Measure and cut. Score the paper face with a utility knife along a T-square, snap the panel along the score line, then cut the back paper. For cement board, score both sides with a carbide knife.
- Hang ceilings first, then walls. Ceilings go up before walls so the wall panels support the ceiling panel edges.
- Fasten to framing. Use 1-1/4 inch coarse-thread drywall screws for 1/2-inch panels, spaced every 12 inches along framing members. Sink screws just below the surface without breaking the paper face.
- Stagger joints. Offset seams between adjacent rows by at least 4 feet so no seam runs continuously from floor to ceiling.
- Tape and mud. Apply joint compound and paper or mesh tape over all seams, screw heads, and corners. Three coats of compound, each progressively wider and smoother, create an invisible seam ready for paint.
Cost Comparison
Material costs for a 12×12-foot room (approximately 12 sheets for walls and ceiling) break down as follows:
- Standard 1/2-inch drywall: $120-$180
- Moisture-resistant green board: $156-$216
- Mold-resistant purple board: $180-$264
- Fire-rated Type X (5/8 inch): $156-$216
Professional installation including hanging, taping, mudding, and sanding adds $1.50-$3.00 per sq ft, which typically doubles or triples the material cost. DIY hanging saves significantly but requires patience during the taping and finishing stages, which is where most amateurs struggle to achieve smooth, paint-ready surfaces.
Choosing the Right Wallboard for Each Room
Match wallboard type to the specific conditions in each room, and you avoid the single most common drywall mistake homeowners make, which is using standard drywall everywhere regardless of moisture exposure. Standard white board handles bedrooms, living rooms, hallways, and closets. Mold-resistant board belongs in every bathroom, laundry room, and basement. Cement board is mandatory behind any tiled wet area. Type X goes on every wall and ceiling that separates your garage from living space. This targeted approach adds less than $100 to a typical project while preventing problems that cost thousands to fix.
