Flat Roof Drainage Design

Without it pooling water can occur and cause leaks deterioration in the roof membrane and ice formation during winter.

Flat roof drainage design.

However flat roofs depend greatly on proper drainage of rain and snow melt to preserve their integrity. Flat roofs have a long history in the united states especially for commercial construction. This means they require a purpose built flat roof drainage system for the task. Or 12 drains required.

Appendix b in the ipc provides rates of rainfall for various u s. So often we find that inner drains are high on the roof causing water to pool around them. Watch for clogs blockage at the roof drain or scupper. From there the flat roof system you choose will determine the materials you apply.

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. Select number of roof drains and calculate the roof area sloped to each drain. 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. Size vertical storm drainage piping.

Most draining systems on flat roofs have a poor design or are not correctly installed. 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 horizontal storm drainage piping. 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.

Poor drainage can lead to serious issues with flat roofing from leaks to structural damage. Of course the best designed flat roof has the correct amount of pitch to drain the water off naturally. Each of these systems has its own pros and cons. Roofs of this design will have one or more roof drains or scuppers installed.

At page top and at left our photos show a low slope roof surrounded by a parapet. The drainage requirements for flat roofs on buildings present some special problems that we describe and illustrate here. There are roof coating products available if there isn t enough slant or slope to accomplish this. There are three types of drain systems commonly used on flat roofs.

It is very critical to position drains for maximum effect. Take the roof s total square footage and divide by the total square footage handled by one drain. Unlike sloped roofs flat roofs can t rely on gravity alone to prevent water from pooling on their surfaces. 50 000 4 400 11 36.

There are three types of drain systems on a flat roof. Cities based on inches per hour that may fall during a storm of one hour duration and a 100 year return period.