The Octagon Roof Framing with Gazebo Cupola calculator will calculate the rafter lengths for the Octagon with the Gazebo Cupola. The base of the cupola will be an Octagon with a purlin structural ring to support the cupola. The cupola radius is not the same as the purlin radius.
- Cupola Calculations
- Side Wall Length
The cupola side wall length is calculate using the cupola radius.The cupola radius is calculated from the purlin radius. The formula is cupola radius = purlin radius + (( hip rafter width *0.5 ) * tan(22.50°)) - #1 Main 2 Butt Hip Rafter Length
Cut 2 hip rafters at this length. These hip rafters will be installed first. The hip rafter head cut will have the Octagon Hip Rafter Slope Angle for the plumb cut angle and will not be beveled. - #2 Side 2 Butt Hip Rafter Length
Cut 2 hip rafters at this length. These hip rafters will be installed second, against the first two hip rafters. The hip rafter head cut will have the Octagon Hip Rafter Slope Angle for the plumb cut angle and will not be beveled. - #3 Mitered Hip Rafter Length
Cut 4 hip rafters at this length. Set the saw Blade Bevel Angle at 45.00°. The hip rafter head cut will have the Octagon Hip Rafter Slope Angle for the plumb cut angle and be beveled. - #4 Mitered King Common Rafter Length
Cut 8 king common rafters at this length. These king common rafters will be beveled. Set the saw Blade Bevel Angle at 67.5°. The king common rafter head cut will have the Octagon Rafter Slope Angle for the plumb cut angle. - Mitered Hip Rafter Plumb Cut Mark Dimension
Measure along the side of the mitered hip rafter and use this dimension to layout the plumb cut line on the side of the hip rafter for the compound miter angle with the saw Blade Bevel Angle at 45.00°. - Mitered King Common Rafter Plumb Cut Mark Dimension
Measure along the side of the mitered king common rafter and use this dimension to layout the plumb cut line on the side of the king common rafter for the compound miter angle with the saw Blade Bevel Angle at 67.50°. - Compound Miter Angle for Hip Rafter Plumb Cut
This is the hip rafter side cut angle that is produced from the compound cut along the side of the hip rafter. You can use this angle to layout the top of the hip rafter when the saw blade is not long enough to cut the compound miter angle on the hip rafter. - Compound Miter Angle for King Common Rafter Plumb Cut
This is the king common rafter side cut angle that is produced from the compound cut along the side of the king common rafter. You can use this angle to layout the top of the king common rafter when the saw blade is not long enough to cut the compound miter angle on the king common rafter. - Jack Rafter Lengths
The jack rafter lengths are calculated from the O.C. spacing from the king common rafter. The jack rafter lengths are to the long point of the jack rafter side cut.
Pages from the book Holy Grail of Roof Framing Trigonometry and Geometry
Online-- Equal Sided Octagon Geometric & Trigonometric Roof Framing Development
Online-- UnEqual Sided Octagon Geometric & Trigonometric Roof Framing Development
