Minimum Slope For Flat Roof

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.

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. Asphalt shingles minimum roof slope roof pitch r905 2 2. 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.

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. 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. They provide excellent weather resistance great value and now more than ever a tremendous range of beautiful designs and color blends. 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.

The idea is to provide positive drainage toward roof drains so there is no ponding water 48 hours after a rain storm. This means for every 12 horizontal units the roof must rise a minimum of 2 vertical units. The minimum slope for a flat roof is 1 4 per foot or 1 4 12 but some owners or insurance companies require a minimum slope of 1 2 per foot. However you can only use this pitch with built up roofing or specialized synthetic roofing.

Low pitched roofs are generally difficult to maintain and you need special materials to prevent leaks. 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. Asphalt shingles can only be installed on roof slopes of 2 12 or greater.

The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. The minimum roof slope allowed by code for any type of roof is in 12 applicable only to coal tar pitch roof systems.