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Roof Drain Size Formula:
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The roof drain size formula calculates the appropriate diameter for roof drainage systems based on flow rate and velocity. Proper drain sizing is essential for effective water management and preventing structural damage.
The calculator uses the roof drain size formula:
Where:
Explanation: The formula calculates the minimum drain diameter needed to handle a specific flow rate at a given velocity, ensuring efficient water drainage.
Details: Correct drain sizing prevents water accumulation, reduces structural stress, minimizes leakage risks, and ensures compliance with building codes and standards.
Tips: Enter flow rate in m³/s and velocity in m/s. Both values must be positive numbers. For accurate results, use realistic values based on local rainfall data and building specifications.
Q1: Why is velocity important in drain sizing?
A: Velocity affects the efficiency of water flow. Too low velocity may cause debris accumulation, while too high velocity can cause erosion and noise issues.
Q2: How do I determine the flow rate for my roof?
A: Flow rate depends on roof area and local rainfall intensity. Typically calculated as: Q = (C × I × A) / 3600, where C is runoff coefficient, I is rainfall intensity (mm/h), and A is area (m²).
Q3: What is a typical velocity value for roof drains?
A: For vertical drains, velocity typically ranges from 1-3 m/s. Horizontal drains usually have lower velocities around 0.5-1.5 m/s to prevent suction and air locking.
Q4: Are there standard drain sizes available?
A: Yes, drains typically come in standard sizes (e.g., 2", 3", 4", 6"). Always round up to the next available standard size for safety.
Q5: Does this calculator account for multiple drains?
A: This calculator provides the size for individual drains. For multiple drains, divide the total flow rate by the number of drains before calculation.