Roof Slope Ratios

This will give you the rise over run or pitch.

Roof slope ratios.

Slope ratio 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 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. The ridge height is 1 9 to 1 7th the span an angle of 12 5 to 16. Historically roof pitch was designated in two other ways.

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. See below after the table for directions on how to convert any roof slope from one form to another. A ratio of 1 1 62 is known as the golden ratio and therefore the vast majority of roof pitch in degrees charts you see will be working to this ratio at the very least. Roof pitch refers to the slope which the rafter creates.

Roof slope expressed as rise in run degrees and percentage. 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. The following table shows how the same common roof slopes can be expressed using rise in run ratios degrees and percentages. 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.

Last updated july 10 2020.