When a stack is extended above the first floor to receive the discharge of plumbing fixtures, the stack vent must be what?

When a stack is extended above the first floor to receive the discharge of plumbing fixtures, the stack vent must be extended full size to maintain proper function and ensure the effective venting of the plumbing system. The purpose of a stack vent is to allow air to enter the plumbing system, which helps to prevent a vacuum from forming as wastewater flows through. If the vent is not of the appropriate size, it could lead to issues such as slow drainage and potentially harmful sewer gas buildup.

Extending the stack vent full size ensures that it can adequately handle the volume of air needed to balance the pressure within the system, especially with multiple fixtures discharging simultaneously. This adherence to sizing requirements is essential in maintaining plumbing codes and standards, reinforcing the importance of proper ventilation in a plumbing system.