How many fixtures can a 2-inch drain handle?

Q: What size drain pipe do I need for a bathroom?

A full bathroom group (water closet, lavatory, tub/shower) is about 5–6 DFU. A 3-inch branch handles the water closet and the group, while the lavatory and tub branches are typically 1-1/2 to 2 inches. The building drain serving a bathroom is 3 inches minimum, because any drain carrying a water closet must be at least 3 inches.

Q: Does every plumbing fixture need its own vent?

Every trap must be protected by a vent to prevent siphoning, but it does not always need its own individual vent. The IPC allows wet venting, common venting, and circuit venting so a single vent can serve multiple fixtures when arranged within the code’s distance and size limits. Size the vent from its DFU load and developed length.

Question

How many fixtures can a 2-inch drain handle?

Accepted Answer

Under the IPC, a 2-inch horizontal branch at 1/4 inch-per-foot slope carries up to about 6 DFU, and a 2-inch stack handles more. That covers a shower, lavatory, and kitchen sink, but never a water closet — toilets require a minimum 3-inch drain regardless of fixture-unit count.

How many fixtures can a 2-inch drain handle?

Answers