Which standpipe classes require a 4 inch riser for buildings under 100 feet and a 6 inch riser for taller buildings?

Which standpipe classes require a 4 inch riser for buildings under 100 feet and a 6 inch riser for taller buildings?

• A. Class I and Class III standpipes
• B. Class II standpipes
• C. All standpipes
• D. None

Answer: (A)

The key idea is that riser size is determined by the water demand and pressure needed for firefighting across the building height. For standpipes that firefighters use (Class I and Class III), the system must be able to deliver sufficient flow to outlets mounted throughout tall buildings. To achieve that, the riser starts at 4 inches for buildings under 100 feet and increases to 6 inches for taller buildings, compensating for friction losses and pressure drop along the vertical run. Class II is intended for occupant use and uses smaller piping and hose connections, so it isn’t governed by the same height-based sizing that applies to the firefighting-oriented classes. Therefore, the requirement described applies to Class I and Class III standpipes.

The key idea is that riser size is determined by the water demand and pressure needed for firefighting across the building height. For standpipes that firefighters use (Class I and Class III), the system must be able to deliver sufficient flow to outlets mounted throughout tall buildings. To achieve that, the riser starts at 4 inches for buildings under 100 feet and increases to 6 inches for taller buildings, compensating for friction losses and pressure drop along the vertical run. Class II is intended for occupant use and uses smaller piping and hose connections, so it isn’t governed by the same height-based sizing that applies to the firefighting-oriented classes. Therefore, the requirement described applies to Class I and Class III standpipes.