Flat Roof Drainage Design

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.

Flat roof drainage design.

Size horizontal storm drainage piping. So often we find that inner drains are high on the roof causing water to pool around them. Cities based on inches per hour that may fall during a storm of one hour duration and a 100 year return period. Most draining systems on flat roofs have a poor design or are not correctly installed.

Carson dunlop associates explain in their sketch above left that some flat roof designs relying on scupper drains and downspouts provide a set of secondary roof drain scuppers located 2 above the roof membrane. In the case of flat roofs the catchment area is the same as the footprint area of the roof being drained. 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. 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.

Poor drainage can lead to serious issues with flat roofing from leaks to structural damage. This pooling water can cause further issues with the rubber membrane collecting leaves moss and other debris that causes harm to rubber membranes. Most drains are elevated hig. Flat roof drains design and installation are very critical.

They are ideal for climates that don t experience large quantities of rain and moisture. 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. The one challenge with flat roofing is ensuring proper drainage. The 3 most common drain systems of a flat roof flat roofs have unique architectural characteristics that make them desirable in many situations.

Appendix b in the ipc provides rates of rainfall for various u s. From there the flat roof system you choose will determine the materials you apply. This applies for rain falling vertically or if it falls at an angle when blown by the wind. Select number of roof drains and calculate the roof area sloped to each drain.