Minimum Slope For Flat Roof

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 slope for flat roof.

This is the basis for calculating the angle which is approximately a 1 19 degree slope. 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. 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. 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 short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. 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 following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code. This means for every 12 horizontal units the roof must rise a minimum of 3 vertical units.

Asphalt shingles continue to be the most widely installed roof covering option in north america.