Minimum Slope For Flat Roof

In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory.

Minimum slope for flat roof.

Asphalt shingles continue to be the most widely installed roof covering option in north america. This means for every 12 horizontal units the roof must rise a minimum of 3 vertical units. 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. For example the international building code 2018 edition ibc 2018 prescribes a 1 4 12 minimum roof slope for asphalt built up polymer modified bitumen thermoset and thermoplastic single ply and liquid applied membranes in new construction.

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 following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code. The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. This is the basis for calculating the angle which is approximately a 1 19 degree slope.

The minimum roof slope allowed by code for any type of roof is in 12 applicable only to coal tar pitch roof systems.