More Reading:
Rainfall Density in the United States
Refer to plumbing code for rainfall density in different locations in the United States.- IPC - International Plumbing Code
- NSPC - National Standard Plumbing Code
- UPC - Uniform Plumbing Code
Roof Area Calculation
- Calculating roof area based on roof plan plus half of the vertical wall area. Refer to governing plumbing code for requirement. Different plumbing code has different explanation.
- Refer to "Overcoming Code Challenges: Calculating Roof Area for Roof Drain Sizing", PSD, July 2009 by Anjian Lu.
Sizing Roof Drains:
More references: J.R. Smith's Technical Data "HOW TO SELECT A ROOF DRAIN" (Note: link may change).
Storm Drain Sizing
Warning! Different plumbing code has different maximum roof area for a particular roof drain and/or pipe size. Be sure to check the plumbing code enforced in your project area.
How to Use:
- For Roof Drains or Leaders: 1) Enter rain density. 2) Enter roof area. The actual flow will be shown in 2nd column. 3) In the dropdown menu, select pipe capacity expressed as roof area, which is the maximum roof area a pipe can handle and it should be equal to or larger than the actual roof area. 4) The corresponding pipe diameter will be shown on the right. 5) The safety margin are also shown in the last column.
- For Horizontal Piping: 1) Enter rain density. 2) Enter roof area. 3) In the Slope dropdown menu, select design slope. 4) In the Pipe Capacity dropdown menu, select area, which is the maximum roof area a pipe can handle and it should be equal to or larger than the actual roof area. 5) The corresponding pipe diameter will be shown on the right. 6) The safety margin are also shown in the last column.
- Example: Click here to see the example.
- * Cuation! Some plumbing codes may not allow using 1/16 inch per foot (or 0.52%) slope. Also, velocity may be too slow in an oversized pipe.
PlumAL can do more:
- Calculating roof drain and drain piping and check its capacity on spread sheets using UDF.
- Drawing profiles with on-screen adjusting feature.
- Recording and reporting results into the calculation book for submission.
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