Roof Framing Geometry

For example a 5 12 pitch roof will rise vertically 5 for every 12 it goes back horizontally.

Roof framing geometry.

The central angle for an octagon roof is 45. One half of 45 is 22 5. Information gained by means of observation experience or experiment. The pitch or steepness of a roof is often referred to in terms of the amount of vertical rise over a 12 horizontal run.

With overhang selected drag slider to increment decrement birdsmouth seat width to suit. 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. Check overhang to calculate rafter overhang equal to the lower level cut at the full rafter depth. You ll need to draw out the roof framing geometry.

For complex roof framing trigonometry or geometry must be used. Roof framing geometry trigonometry for polygons polygons in mathematical context polygons in carpenters mathematical context central angle pi 2 n working angle pi 2 n 2 plan angle pi central angle 2 exterior angle plan angle 2 s is the length of any side of the polygon n is the number of sides. There is more trigonometry in this book than all of the roof framing books written in english combined. It will take more than just reading to understand roof framing geometry.

There are smartphone apps available which can be used to sight a roof s pitch from the ground. Roof framing geometry is empirical type knowledge.