Determine truss count, spacing, height, and cost for your roof. Covers common truss types and span limits.
Trusses are spaced at regular intervals along the building length. Standard spacing is 24 inches on center (OC), but 16" OC is used for heavier loads.
The peak height of a truss depends on the span and pitch:
The most common residential truss type. Uses a W-pattern of web members for efficient load distribution. Ideal for spans up to 40 feet. Does not allow for attic storage.
Simplest design — single vertical post from the peak to the bottom chord center. Best for small spans (up to 20 feet). Often used for porches and garages.
Two vertical posts with a horizontal strainer between them. Handles spans of 25-40 feet. Provides some attic clearance between the posts.
Designed with a raised bottom chord section to create usable attic space. The "room" is typically 8-10 feet wide for a 30'+ span. More expensive due to additional engineering.
Bottom chord slopes upward to create a cathedral ceiling effect. The ceiling pitch is typically half the roof pitch (e.g., 4/12 roof with 2/12 ceiling).
| Truss Type | Max Span | Attic Use? |
|---|---|---|
| King Post | 20 ft | No |
| Queen Post | 40 ft | Limited |
| Fink (W) | 40 ft | No |
| Howe | 30 ft | No |
| Attic | 40+ ft | Yes |
| Scissor | 35 ft | No |