Flat Roof Drainage Design Guide

Interior drains gutters and scuppers.

Flat roof drainage design guide.

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. Flat roofs are hard to replace. Which type of rainwater outlet can prove beneficial to the design and performance of roof drainage and ultimately the building. Flat roofing does not drain naturally like sloped roofs that can rely on the force of gravity to remove water.

Having sufficient drainage on a flat roof is vital. But now flat roofs often are constructed with fewer layers because of improved waterproofing technology. A rooftop garden or additional outside living space are the top reasons people choose flat roofs. Flat roof drainage falls into 2 main categories gravity drainage and syphonic drainage.

The most critical of these issues is the flat roof drainage systems. Guide to flat roofing drainage systems and epdm. Calculate drains needed. Some pipes are too small to handle the volume of the water.

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. 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. Once the roof levels are designed and approved the selection of the rainwater outlets can be reviewed.

This could mean flat roofs may not raise the same red flags they used to. Most flat roofs suffer from poor drain locations or drain levels that are high. Along with the benefits of a flat roof come unique challenges. With a new structure in the design stages or part completed you need to know that your blueprint is going to work.

The above sizing data is offered as a guide only. Why flat roof drainage is important. When designing a roof it is essential to pay close attention to where the drains are. The result is the number of drains needed.

This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table. On many occasions drains are too high and water cannot flow off. Type of flat roof drainage each drainage low point roof sub area is allocated a roof drain and an overflow drain. This guide explains the advantages and disadvantages of the three most common flat roof drainage solutions.

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.