How Much Slope For A Flat Roof

Flat roofs which aren t perfectly flat require a small slope to allow for water runoff.

How much slope for a flat roof.

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. Low pitched roofs are generally difficult to maintain and you need special materials to prevent leaks. According to the international building code the typical built up flat roof that uses tar or asphalt goes by the guideline that for every foot 12 inches of a flat roof a minimum of inch must step up or down.

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. Generally such roofs have a pitch ranging from 1 2 12 to 2 12. Despite the name all flat roofs need to be slightly angled in some direction. 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. The slope of your roof is the angle at which it inclines or declines.