This measurement is best done on a bare roof because curled up roofing shingles will impair your measurement.
Slope of a roof pitch.
Slope is the incline of the roof expressed as a ratio of the vertical rise to the horizontal run where the run is some portion of the span.
Access one of the rafters then take.
Use a level against the underside of the rafter you re measuring to get the most accurate value.
The slope is the measurement of the rise of the roof to the run of the roof and is expressed as inches per foot in a ratio format.
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.
How do you calculate the slope of a roof.
A roof that rises 4 inches for every 1 foot or 12 inches of run is said to have a 4 in 12 slope.
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.
Locate the level s 12 inch mark.
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.