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Roofs & Roofing

Draining A Flat Roof

Question: I have a flat roof, is there a recommended diameter for the drainage pipe?

Answer: The size of the drainage pipe is relative to the square footage of the area to be drained. The following are the minimum size pipe you should use.

  • Up to 700 square feet - 2 inch
  • 700 to 1,300 square feet - 2 1/2 inch
  • 1,300 to 2,200 square feet - 3 inch
  • 2,200 to 4,600 square feet - 4 inch
  • 4,600 to 13,500 square feet - 6 inch

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