Rainwater Calculation For Roof Drain

Rainwater collection calculation formulas and equations.

Rainwater calculation for roof drain.

Calculate rainwater catchment volume. Plans shall show hose bibs or pump systems for discharge and watering of landscaping. The rainwater capture act of 2012 2012 california stats. To the design of the roof drainage system.

The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain. We all agree that vertical walls contribute flow to roof drains because they collect rainwater when wind driven rain hits and runs down the wall. Roof area to be considered the design capacity for a roof drainage system depends on the quantity of water to be handled. Take the roof s total square footage and divide by the total square footage handled by one drain.

If you find that your roof will generate an overwhelming amount of water it may be more practical to consider how much water you will need. Calculator notes and assumptions. 537 section 2 adds an addendum to the swrcb s or state water resources control board s control of water. Your system will recharge every time it rains so you don t need to estimate.

Increasing from the 5 drain shown to a 6 drain increases the roof area that can be served by about 1 6 x the table data. Factors to be considered in the design of roof drainage sys tems are the area to be drained size of gutters downspouts outlets slope of roof type of building and appearance. Show location of cistern rain barrels. Rain barrels should be designed to store 200 gallons and be located such that roof run off is equally distributed.

Calculator is based on chapter 1 of smacna s architectural sheet metal manual 7th edition asmm. How much water do you need. Or 12 drains required. 1 of rain on 1 000 sf roof will yield 623 gallons.

Rainfall wizard is based on table 1 2 rainfall data and drainage factors page 1 2 1 3 of the architectural sheet metal manual 7th edition. Residents are now encouraged to use cisterns and rainwater collection kits to increase the amount usable water that they have on hand. Rain gutters downspouts shall be shown on plans. Roof area ft2 x precipitation amount in x 0 623 amount collected gallons easy formula to remember.

50 000 4 400 11 36. Roof area m2 x precipitation amount mm amount collected liters. The result is the number of drains needed.