Rainwater Calculation For Roof Drain

The roof area calculation for sizing roof drains is an example of how differences among the codes can challenge the designer.

Rainwater calculation for roof drain.

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. The result is the number of drains needed. To the design of the roof drainage system. 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.

Dropping from the 5 drain in the table to a 3 drain cuts the serviced or drainable roof area to about 0 26 x the roof areas shown in the table. 50 000 4 400 11 36. Calculator is based on chapter 1 of smacna s architectural sheet metal manual 7th edition asmm. Plans shall show hose bibs or pump systems for discharge and watering of landscaping.

The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain. 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. 1 of rain on 1 000 sf roof will yield 623 gallons. Residents are now encouraged to use cisterns and rainwater collection kits to increase the amount usable water that they have on hand.

Roof area m2 x precipitation amount mm amount collected liters. Rainwater collection calculation formulas and equations. Calculator notes and assumptions. Take the roof s total square footage and divide by the total square footage handled by one drain.

Rain barrels should be designed to store 200 gallons and be located such that roof run off is equally distributed. How much water do you need. 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 ft2 x precipitation amount in x 0 623 amount collected gallons easy formula to remember.

The roof drainage outlets and rainwater downpipes are calculated based on the design principles for gravity drainage systems established in ss525 2006 code of practice for drainage of roofs. Or 12 drains required. 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. Rain gutters downspouts shall be shown on plans.

Calculate rainwater catchment volume. 537 section 2 adds an addendum to the swrcb s or state water resources control board s control of water. Show location of cistern rain barrels.