Flat Roof Drain Sump Method #1:

The wood sump box.

Usually, when a contractor encounters a flat roof drain that is sitting too high on the roof, the main “technology” used to “sump” or lower the roof drain has been to build a wood “sump box”.

This is a labor intensive, and ultimately, expensive way to sump a flat roof drain, if only in terms of lost or lowered jobsite production due to the time it takes to construct and install the wood sump box.

Flat Roof Drain Sump Method #2:

The “sump receiver or bearing plate”

What are they?

This is a roof drain accessory that essentially is a flat plate with a hole in the middle that receives the flat roof drain, such as the one shown in the photo below. It is generally included when you buy a cast iron roof drain. It is NOT designed to “sump”  or lower a flat roof drain.

Large Roof Drain Sump Receiver Plate

Rather, it  “receives” the flat roof drain. The roof drain is attached to it and it is set in the roof. SUMP RECEIVERS

Since it doesn’t lower the roof drain, it can leave the roof drain sitting higher than the surrounding flat roof surface.

This in turn can cause large pools of rain water to form on the flat roof. The myriad of problems that result include: Standing rain water on a flat roof

  1. Potential for a roof collapse due to excessive weight. 
  2. Water intrusion into the building resulting in water damage and mold growth. 

Flat Roof Drain Method #3: Sloping the roof


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