Quick Answer
Ideally, a first flush diverter should be installed at locations where the roof's drainage pattern allows for the collection of clean water with minimal contamination from debris, leaves, and other impurities. This often involves installing the first flush device near the roof's edge, where the water flow is generally faster and cleaner. A typical roof pitch of 2.5:12 to 4:12 is suitable for first flush installation.
Ideal Location Considerations
When selecting the ideal location for a first flush diverter, consider the roof’s slope, overhang, and surrounding vegetation. Install the device no more than 6 inches from the roof’s edge to capture the fastest-moving water. A minimum roof slope of 2.5:12 is recommended to prevent backflow and ensure proper water flow.
Calculating Water Flow and Pressure
To determine the optimal location for your first flush diverter, calculate the water flow and pressure at different points on the roof. A general rule of thumb is to install the device where the water flow rate is at least 5 gallons per minute (gpm) and the water pressure is between 5 and 15 pounds per square inch (psi). Use a flow meter or calculate the roof’s water flow rate using the following formula: (Roof Area x Rainfall Intensity x Runoff Coefficient) / 10, where roof area is in square feet, rainfall intensity is in inches per hour, and the runoff coefficient is typically 0.9 for a metal roof.
Installation Tips and Tricks
When installing a first flush diverter, ensure the device is level and securely fastened to the roof. Use a 1-inch NPT (National Pipe Taper) adapter to connect the first flush device to the downspout. Apply a waterproof sealant around the connection to prevent leaks. Consider installing a screen or mesh filter over the first flush device to prevent debris from entering the system.
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