1. What is the BS EN 12056 Equation?

The BS EN 12056 equation calculates the required pipe diameter for roof drainage systems according to UK standards. It ensures adequate drainage capacity while maintaining proper flow characteristics.

2. How Does the Calculator Work?

The calculator uses the BS EN 12056 equation:

Where:

• \( Q \) — Flow rate (L/s)
• \( Fall \) — Gradient or slope (m/m)
• \( 3600 \) — Conversion factor (seconds to hours)
• \( 0.311 \) — Empirical coefficient for drainage calculations

Explanation: The equation balances flow capacity with gravitational flow principles to determine optimal pipe diameter for rainwater drainage.

3. Importance of Pipe Sizing

Details: Proper pipe sizing is crucial for preventing overflow, maintaining adequate flow velocity, and ensuring efficient drainage during heavy rainfall events.

4. Using the Calculator

Tips: Enter flow rate in litres per second (L/s) and fall in meters per meter (m/m). Both values must be positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical flow rate for roof drainage?
A: Flow rates vary by roof area and rainfall intensity, typically ranging from 0.5 to 10 L/s for residential buildings.

Q2: What fall values are commonly used?
A: Standard falls range from 1:40 to 1:80 (0.025 to 0.0125 m/m) depending on pipe material and local regulations.

Q3: Are there minimum pipe sizes for rainwater drainage?
A: Yes, most building regulations specify minimum diameters, typically 75mm for main rainwater pipes and 50mm for branch connections.

Q4: How does pipe material affect sizing?
A: Different materials have varying friction coefficients, but BS EN 12056 provides standardized calculations applicable to common drainage materials.

Q5: Should safety factors be applied?
A: Yes, it's recommended to include safety factors for extreme weather events and future climate considerations in final design.