Gambrel Roof Truss Calculator
A gambrel roof truss calculator sizes the classic barn-style roof with two slopes on each side — a steep lower slope and a shallower upper slope that together maximize interior loft space. Enter your building span and pitch below and this free gambrel roof truss design calculator returns rafter length, ridge height, roof area, truss quantity, and material cost, in both imperial and metric units.
Size Your Gambrel Roof Truss
Enter your building specifications below. Results and the roof diagram update live as you type.
Live Roof Diagram
Results
Estimate Your Project Budget
Automatically calculated from your inputs above in the calculator.
Estimates only. Actual costs vary by region, supplier, and site conditions.
How Gambrel Roof Trusses Work
A gambrel truss uses two roof slopes per side instead of one: a steep lower pitch near the eaves and a shallower upper pitch near the ridge. That break in slope is what creates the extra headroom barns and gambrel-style garages are known for, without adding a full second story.
Gambrel trusses are commonly built in 12 ft, 16 ft, and 24 ft spans for barns, garages, and storage buildings, with the upper loft area used for storage or converted into living space. Because the roof shape is more complex than a simple gable, web bracing and connector-plate placement matter more — always have the final layout reviewed by a truss engineer before ordering.
This calculator models the gambrel profile using your span, pitch, and overhang inputs to approximate rafter length, roof area, and lumber needs. For an exact double-slope cut list, a licensed truss designer will confirm the break-point angle and plate sizing.
Frequently Asked Questions
What span works best for a gambrel barn roof?
Gambrel trusses are commonly built in 12 ft, 16 ft, and 24 ft spans for barns and garages, with the loft-style upper section allowing generous storage or living space above.
How to calculate roof truss size?
Measure the building span (wall-to-wall width) and choose the roof pitch. Truss size is set by the top-chord length (from span & pitch), the overall rise, and the required load. Enter span, pitch and load into the calculator and it returns member lengths, height and quantity.
How far can you span a 2x6 truss?
A 2x6 truss chord can commonly span roughly 20–24 ft depending on grade, spacing, pitch and load. Higher loads or wider spacing reduce the allowable span. Use the span calculator and verify against local building codes and an engineer's design.