Flat Roof Drainage Design

Take the roof s total square footage and divide by the total square footage handled by one drain.

Flat roof drainage design. There are roof coating products available if there isn t enough slant or slope to accomplish this. 50 000 4 400 11 36. From there the flat roof system you choose will determine the materials you apply. This means they require a purpose built flat roof drainage system for the task.

The one challenge with flat roofing is ensuring proper drainage. Select number of roof drains and calculate the roof area sloped to each drain. 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. Watch for clogs blockage at the roof drain or scupper.

Roofs of this design will have one or more roof drains or scuppers installed. Without it pooling water can occur and cause leaks deterioration in the roof membrane and ice formation during winter. The downside to flat roofing however is that it s vulnerable to water damage in a way that other roofing solutions aren t. Each of these systems has its own pros and cons.

There are three types of drain systems commonly used on flat roofs. 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. At page top and at left our photos show a low slope roof surrounded by a parapet. Size vertical storm drainage piping.

However flat roofs depend greatly on proper drainage of rain and snow melt to preserve their integrity. Cities based on inches per hour that may fall during a storm of one hour duration and a 100 year return period. Of course the best designed flat roof has the correct amount of pitch to drain the water off naturally. So often we find that inner drains are high on the roof causing water to pool around them.

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. Appendix b in the ipc provides rates of rainfall for various u s. The result is the number of drains needed. Underneath the basics flat roofs are usually constructed with a ceiling nailed to joists which support a deck usually wood in residential construction a vapor barrier insulation and a roof board.

Most draining systems on flat roofs have a poor design or are not correctly installed. The drainage requirements for flat roofs on buildings present some special problems that we describe and illustrate here. It is very critical to position drains for maximum effect. Size horizontal storm drainage piping.

Flat roofs have a long history in the united states especially for commercial construction. Or 12 drains required.