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24 in on center is standard. Trusses = building length in inches ÷ spacing, rounded up, plus one: a 24 ft garage takes 13 (11 common + 2 gable ends), a 40 ft house 21. At 16 in a 24 ft garage takes 19.
Roof trusses are designed to sit 24 in on center on almost every house and garage in the US: an 8 ft sheet of sheathing lands on five trusses, and 7/16 in OSB rated 24/16 spans 24 in without H-clips under 2021 IRC Table R503.2.1.1(1). Stick-framed rafters are usually 16 in on center, trusses go to 16 in when the designer needs them for heavy snow or tile, and post-frame buildings set trusses 4 to 8 ft apart with purlins between. To count trusses, divide the building length in inches by the spacing, round up and add one, because there is a truss at both end walls: a 24 ft garage at 24 in takes 24 × 12 ÷ 24 = 12 spaces, so 13 trusses (11 common and 2 gable ends), or 19 at 16 in; a 40 ft house takes 21 at 24 in. The spacing on the truss drawings is the one the inspector checks.
Short answer: roof trusses are spaced 24 in on center on almost every house and garage. Count them as the building length in inches ÷ the spacing, rounded up, plus one — 13 for a 24 ft garage, 21 for a 40 ft house — and on a gable roof two of those are gable-end trusses.
| Building length | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|
| 20 ft | 16 | 14 | 11 |
| 24 ft | 19 | 16 | 13 |
| 30 ft | 24 | 20 | 16 |
| 36 ft | 28 | 24 | 19 |
| 40 ft | 31 | 26 | 21 |
| 48 ft | 37 | 31 | 25 |
| 60 ft | 46 | 39 | 31 |
| Spacing | Used for | Roof deck on top |
|---|---|---|
| 24 in o.c. | Standard for engineered roof trusses on houses, garages and sheds | 7/16 in OSB (24/16) — no clips needed |
| 16 in o.c. | Stick-framed rafters, heavy snow or tile loads, or when the truss designer calls for it | 3/8 in (16/0) minimum; most crews still use 7/16 in |
| 19.2 in o.c. | Five spaces per 8 ft sheet; occasionally used to save a truss or two | 3/8 in 24/0 or 7/16 in |
| 4–8 ft o.c. | Post-frame (pole barn) buildings: trusses on the posts, or one on each post plus one between | Purlins across the trusses carry the metal panels |
24 inches on center. Prefabricated roof trusses for houses and garages are designed and built for 24 in spacing almost everywhere in the US, because that spacing suits 4 × 8 sheathing (a sheet lands on five trusses) and 7/16 in OSB spans it without clips. 16 in is used for stick-framed rafters and for heavy loads, and post-frame buildings set trusses 4 to 8 ft apart with purlins between. The spacing on your truss drawings is the one that counts — never move trusses farther apart than the designer specified.
Divide the building length in inches by the spacing, round up, and add one: trusses = ⌈length × 12 ÷ spacing⌉ + 1. A 24 ft garage at 24 in takes 24 × 12 ÷ 24 = 12 spaces, so 13 trusses; a 40 ft house takes 21. On a gable roof the two end ones are gable-end trusses, so a 40 ft gable is 19 common trusses plus 2 gable ends.
13 at 24 in on center: 24 × 12 ÷ 24 = 12 spaces plus one. With a gable roof that is 11 common trusses and 2 gable-end trusses. At 16 in it would be 19.
Yes. A metal roof over solid sheathing uses the same 24 in trusses as shingles. A metal roof screwed to purlins instead of a deck depends on the purlin spacing the panel maker allows, typically 24 in or more for through-fastened panels, and the purlins themselves span between the trusses. Check the panel's span table and the truss drawings for the roof load.
Yes, with the right board. Under trusses at 24 in, hang the ceiling drywall perpendicular to the trusses and use board rated for that spacing — 1/2 in sag-resistant ceiling board or 5/8 in — rather than ordinary 1/2 in wallboard, which can sag between framing, especially under wet-sprayed texture or heavy insulation.
Next: H-clips per sheet if your panels need edge support at this spacing.
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