Roof Slope Ratios

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.

Roof slope ratios.

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. The following table shows how the same common roof slopes can be expressed using rise in run ratios degrees and percentages. 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. For example if you measure 4 inches the pitch of your roof is 4 12.

The ridge height is 1 9 to 1 7th the span an angle of 12 5 to 16. 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. Often you express roof pitch as the ratio between the rise and the run in the form of x 12. Historically roof pitch was designated in two other ways.

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. 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. Commonly used roof pitches were given names such as greek.

See below after the table for directions on how to convert any roof slope from one form to another.