A flat roof of a residence is 50`x 74` all horizontal roof drain pipe slopes at an angle of 1/4 per foot. Maximum rainfall is 3″ per hour. What size vertical drain line would be required to drain this area?

A flat roof of a residence is 50`x 74` all horizontal roof drain pipe slopes at an angle of 1/4 per foot. Maximum rainfall is 3″ per hour. What size vertical drain line would be required to drain this area?