Storm Drainage and Fuel Gas Piping
Storm Drainage and Fuel Gas Piping combines two distinct systems. Storm drainage questions test roof drain sizing, rainfall intensity, secondary drainage, and leaders; fuel gas questions test piping materials, shutoff valves, sediment traps, bonding, and pressure testing.
Storm drainage
Storm drainage is sized from the roof area and the local rainfall rate, not from plumbing fixture units. Primary roof drains and a secondary system or overflow scuppers are required so that a blocked primary drain does not cause roof collapse. Leaders and building storm drains must be sized for the design flow, supported, and protected against backflow where required.
Fuel gas piping
Fuel gas pipe must be approved material, properly supported, and protected against corrosion. A shutoff valve is required at each appliance, and a sediment trap is installed downstream of the shutoff valve and as close to the appliance as practicable. CSST must be bonded. Gas piping is pressure-tested before appliances are connected.
Worked example
A roof area of 1,000 square feet receives a design rainfall of 4 inches per hour. One inch of rain per hour on one square foot is about 0.623 gallons per hour, so 4 inches per hour yields about 2.49 gallons per hour per square foot, or about 2,490 gallons per hour (roughly 41.5 gallons per minute) for the roof. The roof drains and leaders must be selected for that flow, along with secondary drainage.
Traps that cost marks
Sizing storm drains by fixture units instead of roof area and rainfall is a common error. Omitting secondary drainage is another. On fuel gas, candidates place the sediment trap upstream of the shutoff or forget CSST bonding.