How Much Slope For A Flat Roof

Low pitched roofs are generally difficult to maintain and you need special materials to prevent leaks.

How much slope for a flat roof.

Flat roofs which aren t perfectly flat require a small slope to allow for water runoff. Despite the name all flat roofs need to be slightly angled in some direction. 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.

In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory. It takes the manufacturer s recommendations the unique conditions of the roof as well as the skills and the expertise of the installer to arrive at the right slope. The table below shows common roof pitches and the equivalent grade degrees and radians for each. If you imagine the top of a building to be the base of a triangle and the peak of the roof to be the triangle s highest point the slope of the roof is the line that connects them together.

Most roof s have a pitch in the 4 12 to 9 12 range. 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.