Flat Roof Drainage Design Guide

Flat roofing does not drain naturally like sloped roofs that can rely on the force of gravity to remove water.

Flat roof drainage design guide.

When designing a roof it is essential to pay close attention to where the drains are. Once the roof levels are designed and approved the selection of the rainwater outlets can be reviewed. Why flat roof drainage is important. Flat roof drainage falls into 2 main categories gravity drainage and syphonic drainage.

Along with the benefits of a flat roof come unique challenges. Most flat roofs suffer from poor drain locations or drain levels that are high. In order to ensure a finished surface with zero fall a design fall of 1 80 should be used and a detailed structural analysis should account for construction tolerances settlement and for. Your building and location can help determine which drain will fit your roof needs.

This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table. With a new structure in the design stages or part completed you need to know that your blueprint is going to work. Guide to flat roofing drainage systems and epdm. This guide explains the advantages and disadvantages of the three most common flat roof drainage solutions.

Flat roof drainage system specifications designs troubleshooting problems solutions for interior drains on flat building roofs flat roof drains scuppers and screens questions answers about keeping the flat roof drainage system working or about installing new drains in a flat roof. A rooftop garden or additional outside living space are the top reasons people choose flat roofs. Having sufficient drainage on a flat roof is vital. But now flat roofs often are constructed with fewer layers because of improved waterproofing technology.

The result is the number of drains needed. Type of flat roof drainage each drainage low point roof sub area is allocated a roof drain and an overflow drain. The need for flat roof drainage in order to prevent water accumulation and moisture damage flat roofs need to be equipped with special drainage systems. Take the roof s total square footage and divide by the total square footage handled by one drain.

Interior drains gutters and scuppers. On many occasions drains are too high and water cannot flow off. The above sizing data is offered as a guide only. Some pipes are too small to handle the volume of the water.

Some observers suggest it s harder to replace a flat roof than a traditional pitched shingle roof because of the labor required to remove its layers especially on older flat roofs. Flat roof design guide some bauder waterproofing systems are bba approved for use with zero falls but back falls are not acceptable and should be corrected. This could mean flat roofs may not raise the same red flags they used to. If you are considering an epdm flat roof for all or part of your building work then a key question is how water will drain away from the flat surface.

Which type of rainwater outlet can prove beneficial to the design and performance of roof drainage and ultimately the building.