How Much Slope For A Flat Roof

The slope of your roof is the angle at which it inclines or declines.

How much slope for a flat roof.

Flat roofs which aren t perfectly flat require a small slope to allow for water runoff. Low pitched roofs are generally difficult to maintain and you need special materials to prevent leaks. Despite the name all flat roofs need to be slightly angled in some direction. Generally such roofs have a pitch ranging from 1 2 12 to 2 12.

In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory. Most roof s have a pitch in the 4 12 to 9 12 range. This is the basis for calculating the angle which is approximately a 1 19 degree slope. The table below shows common roof pitches and the equivalent grade degrees and radians for each.

This is necessary for allowing water to run off of the epdm membrane surface and towards an appropriate drainage system but this slope doesn t need to be extremely steep and when covering a large property the angle of the flat roof can be near invisible to the naked eye. 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.