How many fixtures can be discharged onto a stack above a stack vented water closet?

The correct answer is based on plumbing codes and practices that govern the discharge of fixtures in relation to plumbing stacks and vents.

In most plumbing codes, a stack vent is designed to allow for the proper ventilation of the drainage system, helping to maintain neutral air pressure within the pipes and preventing sewer gases from entering the building. When a water closet discharges into a stack that is vented, it can accommodate additional fixtures discharging into the same stack.

The standard number of fixtures that can discharge onto a stack above a stack vented water closet is typically four. This figure is widely accepted in plumbing design as it ensures adequate drainage and ventilation while minimizing the risk of clogging or backflow. It's essential to adhere to these limits to maintain system efficiency and comply with local plumbing regulations.

This number can sometimes vary based on specific local codes or unique system configurations, but four is a common ruling for both residential and commercial applications.