Minimum Angle For Flat Roof

Some online information indicates flat roofs are less that 1 5 degrees slope and other info says less than 10 degrees.

Minimum angle for flat roof.

The minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run. In the uk the typical house has a pitch between 40 50 although 45 should be avoided. A relatively steep pitch in excess of 40 degrees to be waterproof. Buildingregs4plans flat roof guidance provides information on flat roof drainage guttering weathering details falls cavity trays.

In the usa the range of standard pitches is anywhere between 4 12 and 9 12. Technology has improved to install non penetrating ballast systems to prevent leakage. Flat roofs that are truly horizontal can have a ballast or attached system put in place to create a pitch of at least 10 degrees. According to this code the minimum slope for asphalt shingles is 17 degrees or two vertical units to twelve units in the horizontal.

Contemporary houses often have flat roofs which shouldn t be completely flat but should be around 1 40. This is the basis for calculating the angle which is approximately a 1 19 degree slope. 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. A small strip of timber angle fillet a minimum 75mm x 75mm is fitted under the felt and fixed firmly to the deck.

However you can only use this pitch with built up roofing or specialized synthetic roofing. 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. 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. More modern tiling and felt shingle systems can achieve lower slopes down to about 20 degrees.

This is the basis for calculating the angle which is approximately a 1 19 degree 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. For slopes below 20 degrees systems such as epdm fibreglass metal roofing can be used. Some degree of tilt 3 to 4 degrees is best able to help keep solar panels clean when it rains.

The waterproofing membrane must be taken up the wall at least 150mm providing an upstand.