What is the pitch of a roof
The pitch of a roof is the height of the roof (rise) it obtains after a certain distance (run). Typically the pitch of a roof is expressed as the amount of rise measured in inches in a one-foot run (12"). eg a 6 / 12 for every 12 inches of horizontal length the roof height increases by 6 inches.
There are several ways of getting the pitch and the easiest way is using a framing square.
A framing square, L shaped, has two parts the body (wider part) and the tongue(skinny part).
Place a ladder where you can safely reach the roof on the gable side and set the body of the square at 12" level across from the edge of the roof and read the measurement on the tongue where it is even with the top of the roof. Take both these measurements from the same sides eg if you are using the bottom of square horizontal then read the tongue measurement on the outside. If you are using the top of the body horizontal read the tongue measurement on the inside of the square.
If you don't have a square draw an imaginary level line (a) inward from the edge of the roof. @ 12" measure vertically (b) upwards from this line to the edge of the roof for the rise measurement. The gable overhang will make this a bit harder to get an accurate measurement.And another way to do it involves a bit of math
- measure the total length of the wall.
- measure the height of the roof from top of wall to peak
- measure the heel height of the truss or rafter ( the height of the roof structure above the top plate of the wall)
- subtract the heel height measurement from the height measurement = rise
- divide the length measurement by two = run
- divide the rise by the run and you have the decimal value of your rise in 12" of the run.
Example: length = 20' height = 5' 6" heel height = 6" Convert everything to the same units. Length 20 * 12 = 240" Height 5 * 12 +6 = 66" divide the length in two 240/2 =120" = the run subtract the heel height from the height 66 - 6 = 60" = the rise divide the rise by the run amount. 60 / 120 = 0.5 in decimal format. Covert this to inches by multiplying the decimal by 12 *12 = 6". The pitch of your roof is 6 / 12.
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