Roof Slope Ratios

Last updated july 10 2020.

Roof slope ratios.

For example if you measure 4 inches the pitch of your roof is 4 12. If the rise is 6 inches for every 12 inches of run then the roof slope is 6 in 12 the slope can be expressed numerically as a ratio. You can assess this in two ways either as the roof pitch angles which the rafters make with the horizontal or the proportion between the run and the rise of the roof. A ratio of the ridge height to the width of the building span and as a ratio of the rafter length to the width of the building.

Historically roof pitch was designated in two other ways. Roof pitch refers to the slope which the rafter creates. This will give you the rise over run or pitch. The ridge height is 1 9 to 1 7th the span an angle of 12 5 to 16.

Simply locate a roof rafter board place the end of the level against the bottom edge and measure from the 12 inch mark vertically to the bottom edge of the rafter. Often you express roof pitch as the ratio between the rise and the run in the form of x 12. Roof slope expressed as rise in run degrees and percentage. See below after the table for directions on how to convert any roof slope from one form to another.

Commonly used roof pitches were given names such as greek.