Basement Bathroom Rough-In Basics

What a rough-in includes

A typical rough-in has a 3 inch toilet drain, a 2 inch shower or tub drain and a 1½ inch sink drain stub, all capped at the floor, plus a vent pipe stub in the wall or ceiling. Their locations were set by the builder, so your layout often has to work around them.

Check before you design

• Measure the toilet stub from the planned finished wall to set the rough-in size.
• Confirm each stub is connected and slopes toward the main drain.
• Find the vent and confirm it ties into the main stack.
• Look for a backwater valve and where its access will sit.

When there is no rough-in

If there are no stubs, the concrete must be cut and trenched to reach the main drain. Where the new fixtures are lower than the sewer, an ejector or macerating system pumps waste up to the main line. These need a sealed basin, venting and a check valve.

Supply lines and shut-offs

Hot and cold lines are teed from the nearest trunk lines, with a shut-off for the new bathroom so it can be isolated. A pressure-balancing shower valve is required for scald protection.

Order of work

1. Plan layout around existing stubs.
2. Frame walls.
3. Plumb drains, vent and supply; inspect.
4. Insulate, drywall and finish.
5. Set fixtures and test.

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