Slope Of A Roof Pitch

The run is the measurement from the outside of one wall s top plate to a point directly below the center of the ridge picture a right triangle.

Slope of a roof pitch.

The most precise way to find the roof s slope is by measuring it from the underside. The table below shows common roof pitches and the equivalent grade degrees and radians for each. How do you calculate the slope of a roof. This ratio is always expressed as inches per foot.

Squaring building lines example the picture below shows the pitch of a 7 12 roof slope meaning that for 12 of horizontal measurement roof run the vertical measurement roof rise is 7. This measurement is best done on a bare roof because curled up roofing shingles will impair your measurement. Use a level against the underside of the rafter you re measuring to get the most accurate value. A roof that rises 4 inches for every 1 foot or 12 inches of run is said to have a 4 in 12 slope.

Locate the level s 12 inch mark. Access one of the rafters then take. A pitch over 9 12 is considered a steep slope roof between 2 12 and 4 12 is considered a low slope roof and less than 2 12 is considered a flat roof.