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Roof Drainage Formula:
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Roof drainage calculation determines the flow rate of water that needs to be managed from a roof surface during rainfall. This is essential for proper gutter and downspout sizing to prevent water damage.
The calculator uses the roof drainage formula:
Where:
Explanation: The formula calculates the volume of water that needs to be drained from a roof surface per second during rainfall events.
Details: Proper roof drainage calculation is crucial for designing effective gutter systems, preventing water accumulation, avoiding structural damage, and managing stormwater runoff in compliance with local building codes.
Tips: Enter rainfall intensity in inches per hour and roof area in square feet. Both values must be positive numbers for accurate calculation.
Q1: What is a typical rainfall intensity value?
A: Rainfall intensity varies by location. Common design values range from 2-6 in/hr, but local building codes often specify required values for drainage calculations.
Q2: How do I measure roof area for this calculation?
A: Measure the horizontal projection of the roof, not the actual sloped surface area. For complex roofs, calculate each section separately and sum the results.
Q3: Why divide by 360 in the formula?
A: The divisor 360 converts inches per hour over square feet to cubic feet per second (1 in/hr = 1/12 ft/hr, and 1 hour = 3600 seconds, but the formula simplifies to /360).
Q4: What factors affect roof drainage requirements?
A: Roof pitch, surface material, local climate, building codes, and gutter/downspout configuration all influence drainage requirements.
Q5: How does this relate to gutter sizing?
A: The calculated flow rate determines the required capacity of gutters and downspouts. Gutters should be sized to handle the peak flow rate with some safety margin.