What decides the cost of a tub to shower conversion

Nearly three thousand searches a month ask what this conversion costs, and the pages answering them mostly publish a range. A range is easy to write and hard to defend, because the same job in two houses on the same street can be two different jobs once the tub is out. What follows is the list of things that actually move the number, in the order they usually move it.

Why there is no figure on this page

A published number becomes an anchor. Whatever a real quote says afterwards is read against it, and the reader ends up judging an estimate they can verify by a figure they cannot. We would rather hand over the list of variables and let the quote be checked against the room. Every item below is something we look at on the first visit a local firm makes.

Where the drain is, and where it has to go

This is the largest single variable, and it is the decision the whole conversion turns on. A shower drain that lands close to the old tub waste is a short piece of plumbing. A drain that moves means opening the floor, working between or through joists, and achieving fall to the existing waste line. Whether that is straightforward depends on which way the joists run and what is underneath the bathroom, and it is the first thing we check.

What is under the floor

A bathroom over a basement or a crawl space gives access from below. A bathroom on a concrete slab does not, and moving a drain there means cutting concrete. A bathroom on an upper floor means the ceiling below is part of the job. These are three different amounts of work for the same finished shower.

Curbless costs more than curbed, and here is where

Not in the tile. In the framing: recessing the subfloor so the shower floor finishes level with the bathroom floor is structural work, and whether it is possible at all depends on the joists. Where it is not possible, a low curb is the correct answer rather than a compromise. The build up is set out on the shower conversion page.

The waterproofing system, and the test

Membrane systems differ in material, in how they are bonded and in how the drain is integrated. A quote should name the system rather than say waterproofing, because the word on its own covers both a proper bonded assembly and a coat of something rolled on. The flood test before tiling is time on site, and it belongs in the price rather than being the thing that quietly disappears from a cheaper version of the same quote.

Tile, glass and fixtures

Tile size changes labour more than material: large format on a sloped floor takes longer and asks more of the substrate, and mosaic on the floor means more grout lines and more setting time. Glass ranges from a curtain rail to a fixed panel to a hinged enclosure, and the frameless versions are made to measure after the walls are tiled. Valves, seats and bars are specified individually, and blocking for a seat or a bar is cheap while the wall is open and expensive afterwards.

What demolition uncovers, and how it is priced

Soft subfloor and damp framing behind an old alcove are common, and what the removal exposes moves a shower figure as much as anything chosen from a catalogue. No quote can include them honestly before the tub is out. What a quote can include is the method: how a change is documented, priced and approved before the work continues. A firm that has no answer for that question has one for it on the day, and it will not be in writing.

What lets you compare two quotes

Itemisation. A single figure cannot be compared to anything. A quote broken into demolition, plumbing, floor build up, waterproofing, tile, glass and fixtures can be set beside another quote line by line, and the gaps show up immediately. What to ask for is set out in the article on judging an installer, and the same variables drive every project on this site.