An attic truss carries a clear rectangular room inside the roof, with the webbing pushed out to the sides instead of filling the middle. Typical span: commonly 26 to 40 ft, because the room needs span to be worth having. Truss count comes from the building length rather than the span — divide the length by the spacing, add one, then add two gable-end trusses.
An attic truss carries a clear rectangular room inside the roof, with the webbing pushed out to the sides instead of filling the middle. This page gives the truss count at 24 and 16 inch centres, the rafter length and the ridge height for the spans a attic truss is normally used at, along with what distinguishes it from a standard fink truss, where it fits, and the constraint that decides whether it will work on your building. Typical span: commonly 26 to 40 ft, because the room needs span to be worth having.
| Span | 4/12 rafter | 6/12 rafter | 8/12 rafter | 6/12 ridge height |
|---|---|---|---|---|
| 16 ft | 8.4 ft | 8.9 ft | 9.6 ft | 4 ft |
| 20 ft | 10.5 ft | 11.2 ft | 12 ft | 5 ft |
| 24 ft | 12.6 ft | 13.4 ft | 14.4 ft | 6 ft |
| 28 ft | 14.8 ft | 15.7 ft | 16.8 ft | 7 ft |
| 32 ft | 16.9 ft | 17.9 ft | 19.2 ft | 8 ft |
| 40 ft | 21.1 ft | 22.4 ft | 24 ft | 10 ft |
A attic truss changes the webbing inside the outline, not the outline itself, so the rafter length and ridge height are the same as any other truss at that span and pitch.
Truss count comes from the building length, not the span. Divide the length by the spacing, add one for the final end, then add the two gable-end trusses.
| Building length | At 24 in centres | At 16 in centres |
|---|---|---|
| 24 ft | 15 | 21 |
| 32 ft | 19 | 27 |
| 40 ft | 23 | 33 |
| 48 ft | 27 | 39 |
| 60 ft | 33 | 48 |
Counts include the two gable-end trusses, which are a separate component from the commons and are ordered as such.
| Typical span | Commonly 26 to 40 ft, because the room needs span to be worth having |
|---|---|
| Best for | Getting a usable room or real storage out of the roof space on a new build |
| Watch for | It must be specified at design stage — a standard truss can never be converted into one |
An attic truss carries a clear rectangular room inside the roof, with the webbing pushed out to the sides instead of filling the middle.
Commonly 26 to 40 ft, because the room needs span to be worth having. The exact limit depends on the timber species and grade, the spacing, and the snow and wind loads for your area, so the truss designer sets it rather than a table.
Divide the building length in inches by the spacing and add one, then add two gable-end trusses. A 40 foot building at 24 inch centres needs 21 common trusses plus two gable ends.
No. Cutting, notching or drilling any truss voids its engineered design. If it does not fit, the answer is a redesign from the truss plant, not a saw.