Minimum Slope For Flat Roof

The following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code.

Minimum slope for flat roof.

Low pitched roofs are generally difficult to maintain and you need special materials to prevent leaks. Flat roof slope minimum 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. Asphalt shingles continue to be the most widely installed roof covering option in north america. Flat roofs which aren t perfectly flat require a small slope to allow for water runoff.

The idea is to provide positive drainage toward roof drains so there is no ponding water 48 hours after a rain storm. Generally such roofs have a pitch ranging from 1 2 12 to 2 12. They provide excellent weather resistance great value and now more than ever a tremendous range of beautiful designs and color blends. However you can only use this pitch with built up roofing or specialized synthetic roofing.

The minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run. In order to achieve this drop a slightly steeper angle of 1 40 1 44 should be the aim when installing a flat roof as this accounts for surface. Normally 1 80 0 72 is the recommended minimum angle for a slope and this is universal across the vast majority of flat roofing systems regardless of the materials that they incorporate. Asphalt shingles minimum roof slope roof pitch r905 2 2.

The minimum roof pitch for shedding snow is around 30 or a 6 12 or 7 12 slope although this is not a definite as the material of your roof the direction of the snow and wind are some factors that can affect whether or not snow will slide as roofs of as little as 10 have been reported to shed snow. The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. This means for every 12 horizontal units the roof must rise a minimum of 2 vertical units. In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory.

This is the basis for calculating the angle which is approximately a 1 19 degree slope. 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.