Fan Truss Calculator
A Fan truss adds extra diagonal web members radiating out from near the ridge, beyond what a standard Fink truss uses, to handle longer spans and heavier loads without oversized chord members. This calculator sizes a Fan-style truss from span and pitch and returns rafter length, quantity, and material cost.
Size Your Fan Truss
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Estimate Your Project Budget
Automatically calculated from your inputs above in the calculator.
Estimates only. Actual costs vary by region, supplier, and site conditions.
When to Use a Fan Truss Over a Fink Truss
As span increases beyond roughly 36 ft, a simple two-diagonal Fink web pattern starts requiring impractically large chord members to control deflection and bending. A Fan truss solves this by adding two or more extra web members that "fan" out from a point near the ridge down to multiple points along the bottom chord, spreading the load across more, shorter members.
The additional webs in a Fan truss shorten the unsupported length of both chords between panel points, which reduces bending stress and lets the truss use smaller, more standard lumber sizes even at longer spans — a direct trade of more (but smaller) members for fewer, larger ones.
Fan trusses are common in wide agricultural buildings, garages, and commercial roofs where a Fink or single-Howe layout would otherwise demand oversized or engineered-wood chords; compare this calculator's span and cost output against the standard Fink and Garage/Barn calculators for your project.
Frequently Asked Questions
What is a Fan truss?
A Fan truss is a roof truss web pattern with extra diagonal members radiating from near the ridge to multiple points on the bottom chord, used for longer spans and heavier loads than a standard Fink truss can efficiently handle.
When should you use a Fan truss instead of a Fink truss?
Once span exceeds roughly 36 ft or roof loads increase significantly (heavy snow regions, wide agricultural buildings), a Fan truss's extra webs keep chord sizes reasonable where a simple Fink layout would need oversized members.