1/2 inch vs 5/8 inch drywall: where each is used

Where 1/2 inch and 5/8 inch drywall go

On walls the choice is easy. IRC Table R702.3.5 lets 1/2 in board run in either direction on studs up to 24 in on center, and that is what most houses get. Ceilings are where thickness matters, because the board hangs from its fasteners and a wet texture adds weight and moisture while it dries. The table below sorts the common cases.

Beyond the garage, the fire-rated walls in a house are mainly walls between dwelling units in duplexes and townhouses and exterior walls close to a lot line (IRC Section R302). Those follow a tested design that names the board, usually 5/8 in Type X, so build exactly what the listed assembly says.

Ceilings at 24 inches on center and sag-resistant board

Many roof trusses are set 24 in apart. IRC Table R702.3.5 still allows 1/2 in board on that ceiling if it runs perpendicular to the framing. A footnote to the table changes the answer when the ceiling gets a water-based texture, hand or spray applied. Then the board must run perpendicular, and at 24 in on center it must be 5/8 in thick or 1/2 in sag-resistant gypsum ceiling board.

Sag-resistant ceiling board is a 1/2 in product made to the ceiling-board requirements of ASTM C1396, which include a test for how far the board deflects in humid conditions. It lets a crew keep 1/2 in board on a textured truss ceiling instead of moving up to 5/8 in. Insulation laid on top of the ceiling also loads the board, so check the board maker's limits for blown-in insulation weight over 24 in framing.

Type X and the garage separation under IRC R302.6

Type X is gypsum board with a fire-resistant core, defined in ASTM C1396. It is sold in 1/2 and 5/8 in, and 5/8 in Type X is what most plans mean by "Type X". The separation between an attached garage and the house has three parts in Table R302.6:

• Walls and ceilings between the garage and the house or its attic: at least 1/2 in gypsum board on the garage side.
• A garage ceiling with habitable rooms above: at least 5/8 in Type X gypsum board. The Table R702.3.5 footnote adds that this board runs perpendicular to the ceiling framing, fastened at 6 in on center or closer.
• Walls, beams or posts that hold up that floor/ceiling: at least 1/2 in gypsum board.

Seal the gaps around pipes, ducts and wires where they pass through it. Some states and towns amend these rules, so check with your building department before you order.

Sound, dents and weight per sheet

Sound. A thicker, heavier board blocks a little more airborne sound, but swapping 1/2 in for 5/8 in on a single layer makes a modest difference. Sound ratings (STC) belong to a whole tested wall, as listed in the Gypsum Association's GA-600 manual: the studs, the insulation, the number of layers and how they are attached all count. For a quiet bedroom or media room, follow a listed assembly instead of relying on board thickness alone.

Dents and flatness. The extra 1/8 in makes 5/8 in board stiffer between framing members and harder to dent, which helps on ceilings that show every wave under a raking light and in hallways and garages that take knocks.

Weight. 5/8 in Type X runs about 2.2 lb/ft², against 1.6 for 1/2 in regular and 1.3 for 1/2 in lightweight. A 4 × 12 sheet weighs about 62, 77 and 106 lb respectively, so each 5/8 in sheet carries about 29 lb more up the ladder. Over a whole ceiling it adds up:

A 24 × 24 ft garage ceiling in 5/8 in Type X is about 1,478 lb of board. Rent a drywall lift for ceilings, plan on two people for any 12 ft sheet, carry sheets on edge, and spread a delivery across the floor instead of stacking it in one spot over a single span. For the weight of every sheet size, see the drywall sheet sizes chart.