How does the roof drainage calculator work?
Rainfall-flow calculation from specified design inputs. It is not a universal gutter, downpipe or overflow sizing rule. Effective catchment can differ from plan area where walls or wind affect collection. Use the required method and verified outlet capacity.
Which measurements do you need for roof drainage?
Effective catchment can differ from plan area where walls or wind affect collection. Use the required method and verified outlet capacity. Measure the actual installed geometry or quoted quantity rather than substituting a nominal product size.
Which formula calculates roof drainage?
Runoff (L/s) = effective catchment area (m²) × rainfall (mm/h) × runoff coefficient / 3,600.
What does a roof drainage worked example show?
A 100 m² effective catchment at 100 mm/h and coefficient 1 produces 2.7778 L/s.
Which units apply to roof drainage?
Use the labeled units in the input reference below. The Imperial / Metric selection converts fields with dynamic unit labels. Fixed-unit fields retain the units printed in their labels.
Leave optional inputs blank when unavailable. Required fields and paired data are checked before a result is displayed.
| Input | Units | When used |
|---|---|---|
| Effective catchment area (m²) | as labeled | all modes |
| Design rainfall intensity (mm/hour) | as labeled | all modes |
| Verified runoff coefficient (0 to 1) | as labeled | all modes |
| Verified capacity per outlet (L/s) | as labeled | all modes |
Which assumptions change the roof drainage result?
Rainfall-flow calculation from specified design inputs. It is not a universal gutter, downpipe or overflow sizing rule. Effective catchment can differ from plan area where walls or wind affect collection. Use the required method and verified outlet capacity.
How should you check the roof drainage estimate?
Effective catchment can differ from plan area where walls or wind affect collection. Use the required method and verified outlet capacity. Keep measured values separate from any extra allowance or quoted price. Check the resulting unit and rounding before ordering or using the result.
How can you compare roof drainage scenarios?
Calculate one baseline and add it to comparison. Change one measured input or verified product value and calculate again. Comparison keeps the itemized inputs and results so the changed assumption remains visible.
How can you save or share the roof drainage result?
After calculation, copy or share the result, download the worksheet or print the inputs and result. Embed and citation controls are in the header. Clear changes removes the current worksheet, and a browser refresh opens blank numeric inputs.
Which related tools help with roof drainage?
Use Roof Pitch Calculator, Rafter Calculator, Roofing Calculator for related project quantities. Each tool has its own scope; avoid transferring a result without checking its unit and assumptions.
