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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