1. What is Roof Runoff Calculation?

Roof runoff calculation estimates the amount of rainwater that can be collected from a roof surface during a rainfall event. This is important for designing rainwater harvesting systems and managing stormwater.

2. How Does the Calculator Work?

The calculator uses the roof runoff formula:

Where:

• \( Rainfall \) — Amount of rainfall in inches
• \( Roof\ Area \) — Surface area of the roof in square feet
• \( 0.623 \) — Conversion factor (gallons per square foot per inch of rain)

Explanation: The formula converts rainfall depth over a roof area into volume of water in gallons, accounting for unit conversions.

3. Importance of Runoff Calculation

Details: Accurate runoff calculation helps in sizing rainwater collection systems, designing proper drainage, and understanding water conservation potential.

4. Using the Calculator

Tips: Enter rainfall in inches and roof area in square feet. For irregular roofs, calculate the footprint area (length × width).

5. Frequently Asked Questions (FAQ)

Q1: How accurate is this calculation?
A: It provides a good estimate but actual collection may be 10-20% less due to evaporation, splash loss, and first-flush diversion.

Q2: Does roof material affect runoff?
A: Most materials have similar runoff coefficients (0.8-0.95), but thatch or gravel roofs may retain more water.

Q3: What's the conversion factor 0.623?
A: It converts inches of rain × square feet to gallons (1 inch over 1 sq ft = 0.623 gallons).

Q4: How to calculate roof area for complex roofs?
A: Break into simple shapes (rectangles, triangles), calculate each area separately, then sum them.

Q5: Can I use this for commercial buildings?
A: Yes, the same formula applies regardless of building size or type.