Minimum Slope For Flat Roof

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 deviations and material deflection among other things.

Minimum slope for flat roof. This means for every 12 horizontal units the roof must rise a minimum of 3 vertical units. The following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code. Asphalt shingles continue to be the most widely installed roof covering option in north america. 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. The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. 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. Minimum roof slope roof pitch r905 4 2 metal roof shingles can only be installed on roof slopes of 3 12 or greater 25 slope.

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