What diameter is typically required for the drainage branch vent?

The typical diameter required for the drainage branch vent is 1 ½ inches. This size is standard in plumbing codes for ventilating fixtures that are not considered to be primary vents for buildings. The drainage branch vent serves to equalize pressure in the drainage piping system and allow sewer gases to escape safely outside, minimizing the risks of clogging and ensuring proper drainage.

Using a 1 ½ inch diameter allows for adequate air flow and pressure equalization while still fitting well within the constraints of typical residential plumbing systems. Larger diameters could lead to unnecessary costs and may not provide any additional benefits in terms of airflow for standard residential drainage applications.

For comparison, options like 1 ¼ inches may be too small for effective venting, while sizes like 2 inches or 4 inches exceed what is typically necessary for branch vents, resulting in increased material and installation costs without corresponding benefits for standard systems.