Slope Flat Roof Drainage

Roof slope created a simple and great fix to a project were crickets were missed and ponding water became an issue for an owner.

Slope flat roof drainage. They would be more accurately called low slope roofs. 6 24 2014 david howard aia said. 6 24 2014 david howard aia said. No roof should be entirely flat but rather should slope either toward the perimeter or toward an interior drainage system.

To design a sloped or flat roof drainage system we need to know the anticipated maximum rainfall rate and the flat or projected roof area. How to calculate the drainage requirements for flat roofs reader question. Is there a rule of thumb for number of roof drains needed on flat roofs. After 48 hours following a rain any roof which still has standing water is known as a ponding roof.

Along with the benefits of a flat roof come unique challenges. The roof drainage outlets and rainwater downpipes are calculated based on the design principles for gravity drainage systems established in ss525 2006 code of practice for drainage of roofs. However flat roofs are not really flat. The most critical of these issues is the flat roof drainage systems.

Level roof decks with tapered insulation whether re roofing or new construction getting the drainage correct on level roof decks is still a challenge for most designers. Getting water off a flat roof sounds like a tricky scenario. With the proper roof slope and drainage installation precipitation is not a problem for buildings with flat roofs. Despite the name all flat roofs need to be slightly angled in some direction.

There are roof coating. Of course the best designed flat roof has the correct amount of pitch to drain the water off naturally. The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain. We were able to make new crickets to the existing roof membrane providing positive water flow to the drains.

Then we were able to correct the owner s ponding water concerns. The 1 2 inch per foot slope is used as it doubles the slope of the structurally sloped roof deck which in this case has a slope of 1 4 inch per foot. This is necessary for allowing water to run off of the epdm membrane surface and towards an appropriate drainage system but this slope doesn t need to be extremely steep and when covering a large property the angle of the flat roof can be near invisible to the naked eye.