There are several things to keep in mind when it comes to flat roof drains. Not all conditions and flat roofs are the same and therefore not all the rules can be applied equally to every roof.
It is important to plan a flat roof drain location according to the volume of water and accessibility for maintenance.
To calculate the volume of water that a particular roof drain might receive one must take into account the size of roof surface plus highest rainfall in an hour the area has seen in the last 20 years. Once those facts are known, calculating the size and total of drains is easy.
Accessibility is essential. When a flat roof drain gets clogged for some reason, then it is vital that it should be in a location where it can be reached relatively easy. Clogged drain strainer can quickly flood an entire roof, causing extensive damage. It is not advisable to have a flat roof drain close to skylights or low profile objects where water could spill over into when a drain is clogged.
The best flat roof drain is those that are installed in a basin. The purpose of the basin is so it could collect debris around the strainer while water can still sill into the drain through the upper parts of the strainer. Watch the video to understand the concept.
Watch these videos on repairing all different areas of a flat roof
Flat Roof Drains
It is always best to have a professional design your drain placement and size. Sometimes a combination of inner drains, scuppers, and gutters can be used to lead water off a roof.
A drain basin is always the best design but will not work without a proper strainer or filter. In the video above you notice the filter. A high filter is better because when leaves accumulate on the bottom perimeter, the water can still flow over into the drain.