Minimum Slope For Flat Roof

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.

Minimum slope for flat roof.

This means for every 12 horizontal units the roof must rise a minimum of 3 vertical units. In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory. 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 roof slope roof pitch r905 4 2 metal roof shingles can only be installed on roof slopes of 3 12 or greater 25 slope.

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. 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.

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.