Roof Drain Sizing Calculator
The Roof Drain Sizing Calculator picks the drain and leader size for a roof area at a design rainfall intensity. Example: for a 300 m² roof with 3 drains at 150 mm/h design rainfall, Drain size = 200 mm, Total flow = 12.5 L/s, Leader size = 200 mm (per IPC 2021 | Philippine Plumbing Code).
How it works
Computed from your inputs per IPC 2021 | Philippine Plumbing Code.
Worked example (Plumbing & Pumps)
Inputs: a 300 m² roof with 3 drains at 150 mm/h design rainfall.
| Result | Value |
|---|---|
| Drain size | 200 mm |
| Total flow | 12.5 L/s |
| Leader size | 200 mm |
Computed live by WorkHive's calculation engine; standard: IPC 2021 | Philippine Plumbing Code.
How to use this calculator
- Enter the figures for the duty you are sizing: the worked example below uses a 300 m² roof with 3 drains at 150 mm/h design rainfall.
- The calculator returns Drain size, Total flow, Leader size, computed per IPC 2021 | Philippine Plumbing Code.
- Check the worked example to confirm the method matches how you would do it by hand, then run your own numbers in the interactive tool.
FAQ
What is a roof drain sizing calculator rainfall?
The Roof Drain Sizing Calculator is a free online tool that computes picks the drain and leader size for a roof area at a design rainfall intensity. It shows the formula and a fully worked example so you can check the method, not just the number.
How is it calculated?
The result is computed from your inputs following IPC 2021 | Philippine Plumbing Code. The worked example on this page shows a real computation with real numbers.
Is the calculator free?
Yes. WorkHive's engineering calculators are free to use, no sign-up needed for the tools. WorkHive is a free, offline-first maintenance platform built for Philippine industrial plants.
Run it on your own numbers
Open the interactive Roof Drain Sizing Calculator in WorkHive: free, no sign-up needed for the calculators.