Ontario's Plain-English Guide to Custom Home Buildingπ 705-533-1633 | βοΈ 1-866-868-6606 | βοΈ info@icfhome.ca
1/2 Inch vs 5/8 Inch Drywall: Where Each Belongs in a House, the Ceiling Sag Rule, the Cost and the Weight
Drywall, Taping & Painting
1/2 Inch or 5/8 Inch Drywall? Walls, Ceilings, Garages and the Twenty Cents a Foot That Buys a Stiffer House
Most of the house gets 1/2 in. board and that is fine. The three places that get 5/8 are the ceiling when the joists or trusses are 24 in. apart, the garage side of any wall or ceiling the Building Code wants rated, and anywhere you want walls that do not drum when the door slams. The cost difference is about $0.20 a square foot. The weight difference is the thing your boarder will mention.
The two boards side by side
| 1/2 in. regular | 5/8 in. regular or Type X | |
|---|---|---|
| Sheet cost, 4×8, at the yard | $20 to $23 | $25 to $30 |
| Weight, 4×12 | about 77 lb (62 lightweight) | about 105 lb |
| Max framing spacing, walls | 24 in. | 24 in. |
| Max framing spacing, ceilings | 16 in. (24 in. with sag-resistant ceiling board) | 24 in. |
| Fire rating potential | None rated on its own in a house | Type X: 1 hour in a tested assembly |
| Sound | Baseline | Noticeably deader, about 2 to 3 STC points on the same wall |
| Feel | Fine on 16-in. studs; drums a little on 24-in. | Solid. Hangs pictures better, dents less |
Where each one goes
Walls: 1/2 in. on studs at 16 or 24 in. is what every production house in Ontario uses and it is adequate. I use 5/8 on the walls of custom houses with 24-in. framing because the difference in feel is real and the cost on a 2,000 sq ft house is about $900. On ICF walls the board goes on the foam over plastic webs at 8 in. or 6 in. spacing, and 1/2 in. is plenty. Drywall on ICF.
Ceilings: this is the one with a rule. Regular 1/2 in. board on ceiling framing at 24 in. on centre sags between the trusses within a few years, especially with blown insulation on top of it and a damp summer. The Gypsum Association’s spacing tables say 16 in. for regular 1/2 in. on a ceiling. At 24 in. you use 5/8, or the 1/2 in. “ceiling board” (CGC Sheetrock Sag-Resistant, CertainTeed Easi-Lite ceiling and their like), which is made for it and is lighter than 5/8. Most Ontario roof trusses are at 24 in., so most Ontario ceilings should be one of those two, and plenty are not. Ceilings in detail.
Garage and furnace rooms: the Building Code wants a tight separation between an attached garage and the house, and where the drawings or the inspector call for a fire-resistance rating, 5/8 Type X is how you get it. Walls and especially the garage ceiling if there is a room above. Fire-rated drywall.
Bathrooms and laundry: thickness is not the question there; the facing is. Moisture-resistant board.
The weight is the real cost
A 4×12 sheet of 5/8 is 105 lb. Two men lift it over their heads onto a ceiling, hold it against the lift while one screws, and do that 40 times before lunch. Boarders charge more per foot for 5/8 on ceilings and they are entitled to. If you want 5/8 throughout, expect the hanging rate to go up $0.15 to $0.25 on top of the board cost, and expect them to use a panel lift on every ceiling, which is slower and correct.
Lightweight 1/2 in. (USG Ultralight and the equivalents) came in about fifteen years ago at about 62 lb a 4×12 and it is now the default in most yards. It is fine for walls. The 1/2 in. ceiling board is lightweight too. Where it is not fine is on a wall you want quiet, where the whole point of the mass is the mass.
Where homeowners go wrong
- Regular 1/2 in. on a 24-in. truss ceiling. It looks fine at the walk-through and wavy at year three. Specify ceiling board or 5/8 in writing. The contract.
- 5/8 everywhere “to be safe”. Safe from what? It adds $1,200 to $2,000 on a house and buys you stiffness you will only notice on the 24-in. walls. Spend it on the ceilings and the garage.
- Thinking thicker board is a fire rating. A rating is a tested assembly: the board, the fasteners, the framing, both sides. Type X on one side of an unrated wall is a thicker unrated wall. Why.
- Mixing thicknesses on one wall. The joint between 1/2 and 5/8 is a 1/8-in. step the taper has to float out over a foot. Change thickness at a corner.
Questions people ask
Is 5/8 drywall better than 1/2?
Stiffer, quieter, more fire resistance in a rated assembly, and harder to dent. Also heavier and about $0.20 a square foot more. On walls at 16 in. framing the difference is mostly feel; on 24-in. ceilings it is the difference between flat and sagging.
What thickness of drywall for ceilings?
5/8 in., or 1/2 in. sag-resistant ceiling board, when the joists or trusses are 24 in. apart, which is most Ontario roof trusses. Regular 1/2 in. only on 16-in. framing with no heavy insulation above.
Can I use 1/2 inch drywall in a garage?
Ask your building department what they want on the house side; many want 5/8 Type X on the ceiling under living space and taped 1/2 in. on the walls, some want Type X on both. The detached garage with nothing above it is usually 1/2 in. regular, Level 2 or 3.
How much more does 5/8 drywall cost than 1/2?
About $5 a sheet at the yard and $0.20 a square foot installed, plus a higher hanging rate on ceilings for the weight. On a 2,000 sq ft house, 5/8 throughout is $1,300 to $2,000 more.
Price it both ways
The drywall installation calculator has the board choice built in, so you can see what 5/8 throughout adds to your house before you decide.
Sources and further reading
- Gypsum Association construction standards: GA-216 application and finishing (the hanger’s bible: fastener spacing, ceiling framing limits, joint treatment) and GA-600 fire resistance design manual, with the free downloads.
- CGC Inc.: the maker of most of the board and compound in Ontario; the product sheets give thicknesses, span limits for ceilings and the right compound for each coat.
- Ontario’s Building Code: the official page with the current regulation. Fire separations and garage walls are in Part 9; interior finish flame spread is 9.10.17.
