Flat Roof Drainage Design

Size vertical storm drainage piping.

Flat roof drainage design. Poor drainage can lead to serious issues with flat roofing from leaks to structural damage. Watch for clogs blockage at the roof drain or scupper. At page top and at left our photos show a low slope roof surrounded by a parapet. 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.

50 000 4 400 11 36. It is very critical to position drains for maximum effect. So often we find that inner drains are high on the roof causing water to pool around them. Select number of roof drains and calculate the roof area sloped to each drain.

Cities based on inches per hour that may fall during a storm of one hour duration and a 100 year return period. Without it pooling water can occur and cause leaks deterioration in the roof membrane and ice formation during winter. 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.

There are three types of drain systems commonly used on flat roofs. There are three types of drain systems on a flat roof. 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 drainage requirements for flat roofs on buildings present some special problems that we describe and illustrate here. Take the roof s total square footage and divide by the total square footage handled by one drain. Flat roofs have a long history in the united states especially for commercial construction. However flat roofs depend greatly on proper drainage of rain and snow melt to preserve their integrity.

Size horizontal storm drainage piping. Or 12 drains required. 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. Most draining systems on flat roofs have a poor design or are not correctly installed.

Each of these systems has its own pros and cons. The one challenge with flat roofing is ensuring proper drainage. The downside to flat roofing however is that it s vulnerable to water damage in a way that other roofing solutions aren t. Unlike sloped roofs flat roofs can t rely on gravity alone to prevent water from pooling on their surfaces.

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. The result is the number of drains needed.