Gambrel Roof Calculator
Calculate gambrel roof dimensions, truss measurements, and material requirements for your barn-style roof project. Get accurate estimates for rafters, sheathing, and costs instantly.
Enter building width, desired height, and pitch angles — the calculator returns rafter lengths, roof area, and material estimates.
Roof Dimensions
Calculation Results
Enter your roof dimensions to calculate gambrel roof requirements
Gambrel Roof Calculator Guide
What is a Gambrel Roof?
A gambrel roof is a symmetrical two-sided roof with two slopes on each side. The upper slope is positioned at a shallow angle, while the lower slope is much steeper. This classic barn-style design maximizes usable space in the upper level while maintaining structural integrity.
How to Calculate Gambrel Roof Trusses
- • Determine dimensions: Building width and desired height
- • Set pitch angles: Typically 30° upper, 60° lower
- • Calculate break point: Usually at 50% of half-width
- • Find rafter lengths: Using trigonometry for each section
Typical Gambrel Roof Angles
- • Upper slope: 15° - 40° (typically 30°)
- • Lower slope: 50° - 70° (typically 60°)
- • Traditional barn: 30°/60° combination
- • Modern gambrel: 25°/65° for steeper look
Advantages of Gambrel Roofs
- • Maximum space: More headroom than gable roofs
- • Cost effective: Less material than mansard roofs
- • Classic style: Timeless barn aesthetic
- • Versatile: Suitable for homes, barns, and sheds
Frequently Asked Questions
How do you calculate a gambrel roof?
To calculate a gambrel roof, you need the building width, desired height, and pitch angles for both upper and lower slopes. Use trigonometry to find the rise and run for each section, then calculate rafter lengths using the Pythagorean theorem. Our calculator automates these complex calculations.
What are typical gambrel roof angles?
Traditional gambrel roofs use a 30-degree upper slope and 60-degree lower slope. However, angles can range from 15-40 degrees for the upper slope and 50-70 degrees for the lower slope, depending on your design preferences and local building codes.
How many rafters do I need for a gambrel roof?
Rafters are typically spaced 16 to 24 inches on center. For a 24-foot wide building with 24-inch spacing, you would need approximately 13 trusses. Our calculator determines the exact number based on your building width and standard spacing requirements.
What materials do I need for a gambrel roof?
You'll need lumber for rafters and trusses, plywood or OSB sheathing, underlayment, shingles or metal roofing, and various hardware. Our calculator provides estimates for lumber, sheathing, and roofing materials based on your specific dimensions.
Is a gambrel roof good for snow loads?
Gambrel roofs handle moderate snow loads well due to their steep lower slopes that help shed snow. However, the upper gentle slope may retain some snow. Consult local building codes and consider additional structural support in heavy snow regions.