What Is a Roof Truss?
A roof truss is a structural framework of timber or steel that supports the roof. The most common type is the triangular truss, consisting of top chords (rafters), a bottom chord (ceiling joist), and web members. Trusses distribute the roof load efficiently to the walls below.
Span = total width of the truss
Rise = height from bottom chord to peak
Pitch = rise / run (or rise / (span/2))
Rafter Length = √(rise² + run²)
Common Truss Types
- King Post: Simplest — one vertical post from peak to center of bottom chord
- Queen Post: Two vertical posts for wider spans
- Fink: W-shaped web members, most common residential truss
- Howe: Vertical webs with diagonal members angling toward center
Understanding Roof Pitch
Roof pitch is expressed as rise over run (e.g., 6/12 means 6 inches of rise for every 12 inches of horizontal run). Common residential pitches range from 4/12 to 9/12.
How to Use
Enter the truss span and roof pitch (rise per 12 inches of run). The calculator computes the truss height, rafter length, and roof angle.
Truss Spacing
Residential trusses are typically spaced 24 inches on center. For heavier loads (snow regions, tile roofing), 16-inch spacing may be required.
Engineering Note
Always consult a structural engineer for actual truss design. This calculator provides estimates for planning purposes only.