Bathroom

Tub-to-Shower Conversions: What Moves the Price, and Where Waterproofing Goes Wrong

Most bathroom remodel overruns trace to three things: moving a drain, opening a wall that was not in the plan, and a shower pan built by someone in a hurry.

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A tub-to-shower conversion is the most requested bathroom job in the country, and the quotes for it range from about three thousand dollars to well over fifteen. That spread is not mostly about tile taste. It is about how much of the existing bathroom stays where it is.

The two kinds of conversion

A same-footprint conversion drops a shower base into the exact space the tub occupied, reuses the existing drain location, and puts an acrylic or solid surface wall surround over the studs. Crews that specialize in this can do it in one to three days. It is the honest version of the one-day bath remodel, and for a standard 60 inch by 30 inch alcove it usually works well.

A rebuilt conversion changes the layout, the drain position, the door swing, or the wall construction. The moment any of those change, you are in a real remodel with permits, inspections and a different schedule.

Why moving the drain is the expensive part

A tub drain sits at one end of the tub. A shower drain sits in the center, or wherever the base is molded for it. If the new base does not match the old drain location, the drain line has to move, and that means getting under the floor.

Joist construction versus slab

Over a crawlspace or a basement, moving a drain a foot is a plumber working from below for a few hours, plus possible joist notching that has to respect structural limits. Over a slab, the same move means cutting concrete, trenching, re-plumbing, patching and letting it cure. That single difference commonly swings a quote by two to four thousand dollars, and it is worth asking a contractor to tell you which situation you have before you fall in love with a base that does not fit your existing drain.

Related: the trap arm slope and the vent both have to stay compliant. A drain moved without addressing the vent produces slow drainage and the occasional sewer smell, and it will not pass inspection.

Waterproofing: the part you never see again

In a tiled shower, the waterproofing is what keeps water out of the framing, not the tile and not the grout. Grout is porous by design. Two systems dominate: a traditional mortar bed over a sheet membrane with a clamping drain, and a modern bonded sheet or liquid membrane over a foam or mortar base with a bonding flange drain. Both work when installed correctly. Mixing parts of one with parts of the other does not, and it is a common failure.

Where it actually fails

Corners and changes of plane are where movement concentrates, and they need preformed corners or reinforcing fabric, not just a thicker coat. Curbs need to be wrapped, top and both sides. Niches need to be sloped and fully membraned, and a niche cut into an exterior wall also needs insulation behind it. Penetrations for a mixing valve, a hand shower or a grab bar need to be sealed at the membrane, not just caulked at the tile. And the joint where the wall meets the pan should be caulked with a flexible sealant, never grouted, because grout in a moving joint cracks in the first season.

Ask to see the shower after the membrane is up and before tile goes on. A contractor confident in the work will offer this without being asked, and some will run a flood test on the pan.

Where the money goes

In a typical bid, demolition and disposal is a modest share, plumbing is the volatile piece, the base and surround or the tile package is the visible piece, and labor is by far the largest. Glass is its own line: a framed sliding door is inexpensive, a semi-frameless door is moderate, and true frameless half-inch glass, which usually has to be templated after the tile is set, adds a week to the schedule and a significant amount to the price.

Two items get forgotten on almost every first draft. Ventilation, because a shower in a bathroom with a 50 CFM builder fan will grow mildew no matter how good the tile is, and a properly sized fan ducted to the outside rather than into the attic is cheap while the ceiling is open. And electrical, because older bathrooms often lack a GFCI-protected receptacle, and any circuit you touch is likely to be brought to current code.

Permits, even for a fast job

Homeowners are often told a one-day conversion needs no permit. Rules vary, but in most jurisdictions replacing a fixture in kind is exempt while altering plumbing, moving a drain, or changing framing is not. An unpermitted bathroom alteration can surface later during a sale. If a contractor volunteers that a permit is unnecessary, ask them to point to the local exemption rather than taking it on faith.