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Gambrel Roof Geometry Calculator
Geometric calculator only Geometric calculator only. Check local building regulations for sizes, spans angles etc.

This Gambrel Roof confines to a semicircle, and starts as the top half of an equal sided octagon.
Move slider or directly enter angle to alter sweep angle of lower rafters and change the shape.
Check 'Overhang' to calculate rafter overhang equal to the lower level cut at the full rafter depth.
With overhang selected, move the slider to increment - decrement the birdsmouth seat width to suit.

If using gussets to connect rafters, check the 'Gussets' box and enter top half gusset width to create gusset dimension diagrams. (see diagrams)

Direct Measure Left click, release and drag in main diagram to directly measure dimensions at scale.

Sweep Angle








Need these calculations on-site? Try the site with an iPad or Android Tablet. With a tablet, you can directly measure angles for input to the Roofing and Pitch Angle calculator apps. Lay the tablet on an incline and tap to measure angle. Tap again to capture angle and auto calculate roof, pitch, angles etc. The buttons appear automatically when you visit with a device capable of pitch measurement.



Slider Controls To fine tune Slider Controls click to select and use (cursor) keyboard keys.

Open new window containing only diagram images in current page ↓ This will better fit printed page. Printing to Scale Help
Print all diagrams on current page

Use your iPad or Android Tablet On-Site Your iPad, iPhone or Android Tablet or Phone is a valuable On-Site tool!
Lay your phone or tablet on an angled surface (roof ?) to directly measure angles and automatically calculate Roofing and Pitch Angle Apps.

If you've benefited from this free service, please consider a small donation to
Blue Dragon Children's Foundation


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Contact Us

Greg Tarrant - blocklayer.com - ph: (Australia) +61 7 40987645 - mob: 0438 165 753

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Questions or Suggestions? ph: +61 7 40987645

ALWAYS CHECK WITH YOUR LOCAL BUILDING AUTHORITY BEFORE LAYING OUT OR BUILDING ANYTHING
AND FOLLOW ALL LOCAL CODES. VERIFY ALL DIMENSIONS AND ANGLES BEFORE CONSTRUCTION


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