What is the minimum size of a roof terminal serving a 1 1/2" vent?

The minimum size of a roof terminal serving a 1 1/2" vent is 3". This size is specified to ensure proper ventilation and to accommodate the airflow necessary for venting systems in plumbing.

A 1 1/2" vent is designed to handle a certain volume of air and gases, and the roof terminal must be larger to facilitate efficient venting. A terminal that is too small could restrict airflow, leading to pressure issues or potential blockages in the vent, thereby affecting the plumbing system's functionality.

In plumbing codes and regulations, this sizing rule ensures that the venting system can operate effectively without the risk of causing back pressure or hindrance to the drainage system. The increase in size to 3" provides that necessary capacity while also allowing for proper weather protection and drainage if any moisture enters the vent.