Flat Roof Drainage Design Guide

Drainage devices e g sizes elevations type of material inlet and outlet structures energy dissipators.

Flat roof drainage design guide. The one challenge with flat roofing is ensuring proper drainage. Unlike other roofing types that are slanted or sloped to allow water to drain automatically flat roofs need a built in drainage system to help remove moisture and debris. Size vertical storm drainage piping. The result is the number of drains needed.

The flat roof drainage design guide can go up against different style that when nitty gritty right can ooze a cutting edge feel. Poor drainage can lead to serious issues with flat roofing from leaks to structural damage. Your building and location can help determine which drain will fit your roof needs. The drainage requirements for flat roofs on buildings present some special problems that we describe and illustrate here.

Some pipes are too small to handle the volume of the water. Unless otherwise recommended by a geotechnical engineer lacrc. It is a requirement of building regulation part h that adequate provision is made for rainwater to be carried from the roof of the building. Or 12 drains required.

There are roof coating products available if there isn t enough slant or slope to accomplish this. Of course the best designed flat roof has the correct amount of pitch to drain the water off naturally. Watch for clogs blockage at the roof drain or scupper. Size horizontal storm drainage piping.

Take the roof s total square footage and divide by the total square footage handled by one drain. Roofs of this design will have one or more roof drains or scuppers installed. When designing a roof it is essential to pay close attention to where the drains are. The most critical of these issues is the flat roof drainage systems.

Having sufficient drainage on a flat roof is vital. Show down spout and location of discharge to ground surface which shall be at least 5 feet from foundations walls or to an approved drainage system. Determine 100 year 1 hour rainfall rate used for location of building. Select number of roof drains and calculate the roof area sloped to each drain.

50 000 4 400 11 36. Along with the benefits of a flat roof come unique challenges. Flat roof drain types. On many occasions drains are too high and water cannot flow off.

According to bs 6229 bs 8217 flat roofs should be designed with minimum falls of 1 40 to ensure a finished fall of 1 80 can be achieved allowing for any inaccuracies in the construction. Keep in mind all flat roofs have a slope of between five and 15 degrees to allow water to flow into drain systems such as eaves drainage holes or outlets. At page top and at left our photos show a low slope roof surrounded by a parapet. Most flat roofs suffer from poor drain locations or drain levels that are high.