About the gambrel roof truss
A gambrel truss has two slopes on each side: a steep lower panel and a shallower upper panel. This shape pushes the walls of the roof outward and creates a tall, usable loft or storage space under the roof.
When to choose it
Gambrel roofs are popular on barns, sheds, workshops and cabins where headroom in the upper floor matters more than a simple frame. The calculator models the lower panel as a steep slope and the upper panel at your chosen pitch.
How to use this calculator
- Enter the building span and the length along the ridge.
- Pick the pitch (or switch to an exact angle) and set the eave overhang.
- Choose spacing, material, snow and wind loads. Results update as you type.
The Barn Gambrel example fills in a 24 ft wide, 36 ft long outbuilding with a 4/12 upper slope.
Practical tips
Use the Usable Room Width result to check whether the loft meets the headroom you need. The steep lower panel makes joints at the break point critical, so ask a truss supplier for engineered connector plates there.
Need a different figure? Try the span calculator, the cost calculator or compare options on the all truss types page.