Low Slope Roof Drainage

Low slope roof drainage.

Low slope roof drainage.

Through building drains upper right in the sketch become clogged internally and burst flooding the building or leaks occur around the drain itself where it penetrates the roof. Keeping the roof adequately drained can help keep water from sitting on the roof. The asphalt roofing manufacturers association arma recommends that roof designs provide adequate slope minimum of inch per foot to ensure that the roof drains freely throughout the life of the building and to thereby avoid the effects of ponding water. On flat or low slope roofs that drain to one end lower right in the sketch especially if the building rear wall does not include a projecting eave or soffit a clogged gutter or downspout send water down the building rear wall flooding the structure through its wall or through windows.

One of the most common we see is the lack of proper drainage. A traditional roof on a home is slanted. Consequently the roof drains must be located on the plumbing drawings up slope from the low point. On a flat roof you don t get the same slope so the water has nowhere to go.

The building in figure 2 is located in the mid atlantic region near a large city on the east coast. 4 x 5 downspout scupper box scupper with sleeve closed top scupper with sleeve open top 7 gutter shop fab gutter more search low slope. Prudent designers would like the roof drains to be located at the low point of the structurally sloped roof deck. This allows water to run down the roof into the gutters.

Proper drainage cannot be emphasized enough when discussing or reviewing the requirements of any well drained low slope commercial roof system figure 1.