Flat Roof Drainage Design Guide

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Flat roof drainage design guide.

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. Roofs of this design will have one or more roof drains or scuppers installed. Take the roof s total square footage and divide by the total square footage handled by one drain. Drainage devices e g sizes elevations type of material inlet and outlet structures energy dissipators.

Select number of roof drains and calculate the roof area sloped to each drain. Size vertical storm drainage piping. 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. When designing a roof it is essential to pay close attention to where the drains are.

Having sufficient drainage on a flat roof is vital. Some pipes are too small to handle the volume of the water. The result is the number of drains needed. The most critical of these issues is the flat roof drainage systems.

Most flat roofs suffer from poor drain locations or drain levels that are high. Flat roof drain types. Of course the best designed flat roof has the correct amount of pitch to drain the water off naturally. 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.

At page top and at left our photos show a low slope roof surrounded by a parapet. Size horizontal storm drainage piping. Unless otherwise recommended by a geotechnical engineer lacrc. The one challenge with flat roofing is ensuring proper drainage.

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. Ipc provides four steps to size the roof drains on a building. The flat roof drainage design guide can go up against different style that when nitty gritty right can ooze a cutting edge feel. There are roof coating products available if there isn t enough slant or slope to accomplish this.

Determine 100 year 1 hour rainfall rate used for location of building. 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. There are three types of drain systems commonly used on flat roofs. Or 12 drains required.

The drainage requirements for flat roofs on buildings present some special problems that we describe and illustrate here. Watch for clogs blockage at the roof drain or scupper. Poor drainage can lead to serious issues with flat roofing from leaks to structural damage. On many occasions drains are too high and water cannot flow off.