1. What is the Roof Drain Calculation Formula?

The Roof Drain Calculation Formula (Q = C × i × A) is used to estimate the peak flow rate of rainwater runoff from a roof surface. It helps in properly sizing drainage systems to handle expected rainfall volumes.

2. How Does the Calculator Work?

The calculator uses the roof drain flow equation:

Where:

• \( Q \) — Roof drain flow rate (m³/s)
• \( C \) — Runoff coefficient (unitless)
• \( i \) — Rainfall intensity (m/hr)
• \( A \) — Roof area (m²)

Explanation: The formula calculates the maximum expected flow rate based on roof characteristics and local rainfall data.

3. Importance of Roof Drain Calculation

Details: Proper roof drain calculation is essential for preventing water accumulation, structural damage, and ensuring effective water management in building design.

4. Using the Calculator

Tips: Enter the runoff coefficient (typically 0.8-1.0 for most roofs), rainfall intensity for your region, and total roof area. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical runoff coefficient for roofs?
A: Most roof surfaces have a runoff coefficient between 0.8 and 1.0, with smoother surfaces having higher values.

Q2: How do I determine rainfall intensity?
A: Rainfall intensity data can be obtained from local meteorological records or building codes that specify design storm values for your region.

Q3: Should roof slope be considered?
A: While slope affects drainage speed, the basic formula assumes adequate slope for water to reach drains. Steeper roofs may require additional considerations.

Q4: How does roof material affect calculations?
A: Different materials have varying absorption characteristics, which is accounted for in the runoff coefficient value.

Q5: Should safety factors be applied?
A: Engineering practice often includes safety factors (typically 1.5-2.0) to account for potential clogging and extreme weather events.