Roof Framing Geometry

You ll need to draw out the roof framing geometry.

Roof framing geometry.

Check overhang to calculate rafter overhang equal to the lower level cut at the full rafter depth. The central angle for an octagon roof is 45. However it has over 1 000 geometric roof framing drawings in the book as well for carpenters that are not comfortable using trigonometry. There are smartphone apps available which can be used to sight a roof s pitch from the ground.

The pitch or steepness of a roof is often referred to in terms of the amount of vertical rise over a 12 horizontal run. Move slider or directly enter angle to alter sweep angle of lower rafters and change the shape. With overhang selected drag slider to increment decrement birdsmouth seat width to suit. Gambrel roof framing geometry calculator metric this gambrel roof confines to a semicircle and starts as the top half of an equal sided octagon.

One half of 45 is 22 5. There is more trigonometry in this book than all of the roof framing books written in english combined. Information gained by means of observation experience or experiment. Roof framing geometry is empirical type knowledge.

For complex roof framing trigonometry or geometry must be used. The tangent of 22 5 41421 laying out an octagon using a framing square we would take 12 on the blade and the number to be taken on the tongue is 12 41421 which is 4 97 or nearly 5.