What size common drain pipe must be installed in a stairwell if the system drains are 1 1/2"?

When determining the appropriate size for a common drain pipe in a stairwell system where the system drains are 1 1/2", it is essential to consider both the function of the drain and industry standards. A common drain pipe serves as the main conduit for the flow of wastewater from multiple smaller drains.

Installing a drain pipe that is larger than the individual system drains ensures that it can accommodate the cumulative flow from those drains, preventing potential blockages and allowing for efficient drainage. In this case, a 2" common drain pipe is correctly chosen to provide adequate capacity and minimize the risk of clogs caused by backflow or insufficient drainage.

Considering the demands of drainage systems, using 2" ensures that it adheres to plumbing codes and provides a margin for any increased flow that may occur during peak usage times. Larger drain pipes also facilitate easier maintenance, as they can handle debris and sediment better than pipes that are just the same size as the inlets.