Basement Bathroom Additions in Wentzville, MO

Gravity or ejector: the first question

If your builder left a rough-in, you will see capped pipes coming out of the slab, usually a three-inch toilet stub, a two-inch shower drain and a vent. That rough-in connects to a line under the floor. In many subdivisions around here that line runs by gravity to the sewer because the main is deep enough. In others it runs to a sewage ejector pit, a sealed basin with a grinder or ejector pump that lifts waste up to the main drain.

Neither is a problem, but you have to know which one you have before you design. We scope the line with a camera when there is any doubt. If there is no rough-in at all, we cut and trench the slab, lay new drain with proper slope, tie in the vent, and pour back. It is a loud, dusty two days, and then it is over.

Venting, heat and waterproofing in a room with no window

A below-grade bath almost never has an operable window, so the exhaust fan carries the full load. We size the fan to the room, duct it in rigid or semi-rigid pipe to an exterior termination, and put it on a timer or humidity switch so it keeps running after the shower ends. Showers get a bonded waterproofing membrane behind the tile, not just cement board. Floors get a drain-friendly slope and, if you want it, electric heat mat under the tile, which makes a slab-level bathroom far more pleasant in January.

Sizing it for who will use it

A powder room fits in about twenty square feet and serves a rec room fine. If the basement will have a bedroom, or if guests will stay down there, a three-quarter bath with a real shower is the better investment. We keep the footprint against the rough-in wall where we can, and we place the door so it does not open directly onto the seating area.

How the work runs

1. Locate and scope drainsFind the rough-in or main line, confirm gravity versus ejector, and camera the pipe if its condition is unknown.
2. Layout and fixture selectionFix the toilet, vanity and shower positions, select fixtures and tile so rough plumbing dimensions are exact.
3. Slab work and rough-inSaw-cut and trench if needed, set drains and vents, run supply lines, wire the fan, GFCI circuit and lighting, then inspect.
4. Waterproof, tile and trim outMembrane, tile, grout, vanity, toilet, glass and accessories, followed by the final inspection.

What moves the price

We do not publish square-foot prices, because they mislead more than they help. These are the factors that actually change the number on a proposal.

• Whether a usable rough-in exists. Cutting and trenching concrete is the single biggest swing.
• Ejector pit and pump if gravity drainage is not available.
• Shower type: a prefabricated base with tiled walls costs far less than a fully tiled curbless shower with glass.
• Distance to the vent stack, the panel and the nearest exterior wall for the fan duct.

How long it takes

As a standalone project a basement bath usually takes three to five weeks. Inside a full basement finish it adds roughly one to two weeks to the overall schedule.

Permits

Plumbing and electrical permits are required, and most jurisdictions fold them into a building permit for the finished space. Underground plumbing is inspected before the slab is poured back. See our guide to which projects need a permit.