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Roof runoff peak flow

Estimate peak roof runoff from connected area, rainfall intensity and a runoff factor.

Use horizontal roof projection draining to the selected outlet.
Use a local design intensity for the selected duration and risk.
Fraction of rainfall assumed to reach the drainage system.
Estimated peak runoff

3.00 L/s

Uniform rainfall over the connected roof and a constant runoff factor. Roof geometry, gutter storage, wind, blockage, snow, outlet hydraulics and local sizing rules are excluded.

FROM ESTIMATE TO ACTION

Use the result, not just the number.

01

Verify the inputs

Measure or document each input. If a value is only an estimate, record its source and test a conservative alternative.

02

Keep the calculation traceable

Save the input link or copied result together with the date, units and assumptions. A number without its inputs cannot be checked later.

03

Confirm the decision

Compare the estimate with the related guide, current product data and requirements that apply at your location before buying or building.

Inputs to verify

Connected projected roof area (m²)
Use horizontal roof projection draining to the selected outlet.
Design rainfall intensity (mm/h)
Use a local design intensity for the selected duration and risk.
Runoff factor (%)
Fraction of rainfall assumed to reach the drainage system.

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