Dr-Fix-It! Rafter Inch Rise Calculation

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INCH RISE

"Inch Rise" and the run measurement are all that is needed to obtain all rafter lengths and cuts for common, hip, valley, and jack rafters.

If the "Inch Rise" number is given on the blue prints, you are done! You won't have to calculate your own "Inch Rise" . Just use the "Inch Rise" given. (One of the most commonly used or standard Inch Rise is 8.)

Use this trick to simplifiy the calculation of the Inch Rise: Measure the Rafter Run in Feet and measure the Rafter Rise in Inches. That is all there is to it.

"Inch Rise Per Foot of Run," abbreviated "Inch Rise" = Rafter Rise in Inches divided by Rafter Run in Feet

Inch Rise=Rafter Rise in Inches                  Rafter Run in Feet



TO MEASURE RAFTER RUN:

Measure or calculate the horizontal distance the rafter will run starting at the outside of the wall on which it rests. Include any boarding on the wall if it extends to the wall top plate. For example, we have a building 20' wide, and will build a hip roof ( see illustration )   Our run is 1/2 the width or 10'. (Note: The run does not include the width of the ridge.)

TO MEASURE ROOF RISE:

Measure in feet the length you wish the ridge to be above the wall or obtain this dimension from your blue prints.