Flat Roof Drains Explained – The benefits of having a Back-up drain – scupper

A Scupper as a backup drain or overflow drain will save you on costly repairs later
A backup flat roof drain prevents a roof from ever flooding. It is important to position flat roof drains correctly and to ensure there are scuppers that could lead water off a roof when the strainers get clogged.
There are three types of drains systems that can be used on flat roofs. These are gutters, inner drains, and scuppers. Scuppers and inner drains are often used in conjunction with each other.
The inner drains will be the main roof drain but as a backup, if the inner drain would clog or the strainers would block the water, then a scupper is necessary to be used as an emergency overflow.
Normally a scupper would be placed a few inches higher than the main drain and water would flow off the roof on the side of the building.
In this video, you can see a combination of an inner drain and a scupper. Since there are many trees around that dump their leaves on the roof, these strainers get clogged. This is where a scupper is very essential.