Drain planning starts with all the roof areas that feed the outlet, including higher roofs that discharge onto it. Sizing, overflow protection, and piping should be designed for the building rather than estimated from a generic rule.

What to check first

  • Map the complete contributing roof area.
  • Find low points and obstructions.
  • Have a qualified designer verify capacity and overflow provision.

Separate a leak from a drainage problem

  1. Trace the water route

    Follow water from the roof surface through the inlet and toward the discharge point. Inspect normal drainage and any separate overflow provision.

  2. Check the waterproof connection

    A sound pipe does not prove the membrane-to-drain connection is sound. Look for loose components, separation, damaged flashing, or patch buildup around the inlet.

  3. Preserve the opening

    A compatible local repair must not reduce the effective outlet or cover its strainer. Persistent ponding, backup, or changes to drain location and size need building-specific professional assessment.

Watch the field examples

These archive demonstrations show individual projects. Use the current guidance above and Bergstrom’s published instructions if an older video shows a different product or method. Torch work shown in installation videos is professional work.

Watch Planning Flat Roof Drainage: Catchment and Flow PathsOpens on YouTube ↗

From the project archive

average rainfall table calculator
Historical project photo · Flat Roof Doctor

Product reference: Bergstrom Industries’ published knowledge catalog. Follow the latest product label and safety information. Historical project examples are educational and are not a specification for every roof.