Gambrel Roof Calculator

A gambrel roof is a two-sided roof with two slopes on each side, where the lower slope is steeper than the upper slope. This design is commonly seen on barns and provides more usable space in the upper level compared to a traditional gable roof.

A gable roof has a single slope on each side from ridge to eave, while a gambrel roof has two different slopes on each side - a steeper lower section and a gentler upper section. Gambrel roofs provide more interior space and are more complex to build.

Common gambrel roof angles are 60-70 degrees for the lower pitch and 15-30 degrees for the upper pitch. The steeper lower angle maximizes interior space while the gentler upper angle reduces overall roof height and material costs.

Gambrel roof pitch is calculated using trigonometry. The lower rafter length equals the loft height divided by the sine of the lower angle. The upper rafter length is determined by the loft width and upper angle using cosine calculations.

For a 60-degree lower pitch, the upper pitch typically ranges from 20-30 degrees. A 30-degree upper pitch is common as it provides good proportions and weather protection while maintaining the gambrel's characteristic profile.

A gambrel roof can provide 15-20% more usable upper floor space compared to a gable roof of the same span. The steeper lower slopes allow for taller walls in the loft area, making it more practical for living or storage space.

Gambrel roofs distribute loads more efficiently than simple gable roofs due to their two-angle design. The break point where angles change can be reinforced, and the design naturally sheds water and snow while providing excellent structural integrity.

Gambrel roofs are typically 15-20% more expensive than gable roofs due to their more complex framing and additional materials. However, they often provide better value when considering the increased usable space they create.