Seven expensive mistakes people make buying a shower kit

There is a specific call we take two or three times a month. Someone has bought a shower kit, the installer has pulled the tub out, and something does not work. The drain is in the wrong place, or the unit will not turn the corner at the top of the stairs, or the walls will not take a grab bar and the whole point of the project was the grab bar.

At that stage the options are all expensive. So here are the seven decisions that create those calls, in order of what they cost to fix afterwards.

1. Buying the kit before checking the drain

This is the most expensive mistake on the list and it is almost always avoidable with a flashlight and five minutes.

A bathtub drain sits at one end of the tub, tight against the wall, and it is usually on a 1½-inch line. A shower pan puts the drain somewhere else, often the center, and many pans, especially linear and trench designs, want a 2-inch line.

So the moment the tub comes out, one of three things is true. The pipe lines up, and you are fine. The pipe is close and the pan has an offset that covers it. Or the pipe is in the wrong place and somebody has to move it.

Moving a drain in a house with wood joists means opening the ceiling below, or pulling up subfloor, cutting into joists within the allowable zones, running new pipe at the correct fall, and getting it inspected. Cost estimates for rough-in plumbing on a conversion commonly run from a few hundred dollars up to several thousand when the drain has to move.

On a concrete slab it is worse. You are renting a concrete saw, cutting a trench, removing spoil, running pipe, and re-pouring. That is days, not hours, and it is dust through the whole house.

What to do instead

Before you buy anything, find out three things:

1. Where the existing drain is, as you face the opening: left, right or center, and roughly how far in from the front edge.
2. What the floor is: concrete slab, or wood joists.
3. Whether the bathroom is on the ground floor or above a finished ceiling.

Then buy a pan that suits those answers. Custom drain positions exist precisely for this. Ordering the pan around your pipe is nearly always cheaper than moving your pipe to suit a pan, and on a slab it is not close.

If the drain genuinely cannot be reached — a second-floor bathroom over a finished ceiling, or a post-tension slab — an above-floor-rough unit solves it. Those keep the drain body above the existing floor line and route water out through a trench at the entry. No slab cutting, no joist notching.

2. Picking the size before the threshold height

People fall in love with a footprint. A 60 by 36. A generous corner unit. Then they discover that the entry height they actually need forces a different pan, a different drain, sometimes a different floor detail, and a different price.

Threshold height is the parent decision. Size follows it.

Here is why. A half-inch barrier-free entry has to get water to a drain with very little vertical room to work in. That usually means either a trench drain along the entry edge or a pan that sits lower in the floor structure. Both of those constrain what is possible, and both interact with your joists or your slab.

A two-inch threshold has more room to work with and installs into almost anything. A four-inch curb installs into anything at all.

So decide the entry height first, honestly, for the person who will be using this shower in ten years. Then pick the largest footprint that works with it and fits the room.

How to pick the number

• Half an inch if a wheelchair or a caregiver-pushed shower chair is involved, now or foreseeably. It is also the ADA maximum for a roll-in compartment.
• One inch if you want the entry to stop being a factor without the floor work a half-inch sometimes needs. This is the quiet favorite and we recommend it constantly.
• Two inches for a steady adult in a straightforward retrofit.
• Four inches if water containment matters more than the step and nobody in the house has a mobility concern.

Nobody has ever called us to complain that their threshold was too low. Plenty of people have called to ask what it would take to lower one.

3. Assuming the walls will hold a grab bar

Grab bars get added later in the overwhelming majority of cases. Somebody buys the shower at 62, and at 71 the physical therapist says it is time for a bar.

At that point one of two things is true. The walls have laminated wood backing behind the panels, and a bar can be screwed in anywhere in about twenty minutes. Or they do not, and the bar has to land exactly on a stud, or the wall has to be opened to add blocking.

Studs are 16 inches apart and they are almost never where a grab bar wants to go. The useful position for a bar is a diagonal at the entry, or a horizontal run at a height that suits one particular person's reach. The chance of a stud being in exactly the right place is low.

This is why we push reinforced walls even to people who say they will never want a bar. It is a few hundred dollars now against a wall-opening job later, and the decision cannot be reversed once the shower is in.

Also true of seats

A wall-mounted fold-down seat carries a person's full weight, repeatedly, at the end of a lever arm. It needs more backing than a grab bar, not less. If a seat is even a possibility, the walls need to be backed.

4. Ordering a one-piece unit that cannot physically get in

A one-piece shower is genuinely stronger. No seams, nothing to seal, nothing to align. In new construction, where the unit goes in before the walls close up, it is often the right call.

In a retrofit it is frequently impossible, and people discover this on delivery day.

A 60-inch one-piece unit is a rigid object roughly five feet wide and six or seven feet tall. To get to your bathroom it has to pass through your front door, down a hallway, around whatever corner is there, and sometimes up a staircase with a turn in it. Staircases with a landing and a 90-degree turn defeat them routinely.

Measure the path, not just the room

Walk from your front door to the bathroom with a tape measure. Record:

• The narrowest doorway width.
• The tightest turn, measured as the diagonal you would need to swing through.
• Stair width and whether there is a turn or a landing.
• Ceiling height at the tightest point, because you may need to tilt.

If any of that is questionable, a multi-piece unit is the answer. Modern locking wall joints seal reliably; the seam is not the weak point people assume it is, and a multi-piece unit that fits beats a one-piece unit sitting in your driveway.

5. Trusting the word "ADA" on a product page

This one is not really the buyer's fault. The word gets used as a marketing adjective and it means something specific.

ADA compliance describes a finished compartment and the space around it, not a product in a box. A pan cannot be compliant by itself, because compliance depends on clear inside dimensions, entry width, the position and height of a seat, the location of controls, and the clear floor space outside the opening.

The dimensions that matter

• Transfer compartment: 36 by 36 inches clear inside, a 36-inch entry, and a seat 17 to 19 inches above the floor.
• Standard roll-in: minimum 30 by 60 inches clear inside, a 60-inch entry, and a 30 by 60 inch clear floor space adjacent to the opening.
• Alternate roll-in: minimum 36 by 60 inches clear inside with a 36-inch entry at one end of the long side.
• Threshold: half an inch maximum in a roll-in compartment.

There is a two-inch threshold exception, and it gets quoted constantly by people who have not read it. It applies only to transfer-type compartments in existing facilities, and only where a half-inch threshold would disturb the structural reinforcement of the floor slab. It is not a general permission to build a two-inch entry and call it ADA.

In a private home none of this is legally required. It is still the best available guidance on what dimensions actually work, because it was written by people who measured.

6. Comparing kit prices instead of project prices

A $700 kit and a $2,600 kit look like a $1,900 decision. They frequently are not.

The finished project includes demolition, disposal, drain work, any framing changes, the kit, the valve and fixtures, the install labor, the trim, and a permit if your jurisdiction requires one. For 2026, published figures put an installed walk-in shower at an average near $9,000, with most jobs between $6,000 and $12,000. Tub-to-shower conversions run wider, from roughly $1,200 to $8,000.

Against those numbers, the kit is often a minority of the spend. And the cheaper kit can increase the rest of it.

Three ways a cheap kit gets expensive

1. It does not fit, so a wall gets built out. Carpentry, drywall, paint, and permanently less shower.
2. Its drain does not match, so the pipe moves. The single biggest line item risk in the whole job.
3. Its walls need blocking, so the framing gets opened. More labor, more drywall, more paint.

Compare the whole project. Ask each supplier what their kit does to the plumbing scope and the framing scope. That is the question that separates real quotes from box prices.

7. Measuring the opening once

The cheapest mistake to avoid and one of the most common.

Measure wall to wall at the floor, at about hip height, and near the ceiling. In any house built before about 1990, those three numbers will usually differ. Half an inch is normal. An inch is common. Studs twist, plaster builds up in corners, floors settle, and somebody tiled over the old tile.

Then do the same front to back.

A kit is built to one number, and it has to be the smallest one. If you order to the widest measurement, the unit does not go in. If you order to the narrowest without knowing the others, you may end up with a gap you did not expect.

The full measuring list

• Width at floor, hip height and ceiling.
• Depth at floor, hip height and ceiling.
• Floor to ceiling height, and anything intruding: a soffit, a sloped ceiling, a fan, a light.
• Drain position and rough distance from the front edge.
• Window in the wet wall, if there is one.
• Valve position, if it has to stay where it is.
• The path from the front door to the bathroom.

Photograph all of it. Four corners, the plumbing wall, the doorway, and the room from the hall. A photo answers questions a measurement cannot, and it takes thirty seconds.

Three more that nearly made the list

Buying the shower before looking at the subfloor

When a tub comes out, the subfloor underneath it is exposed for the first time in decades. In a meaningful share of jobs, some of it is soft. A slow leak around an old tub drain or a failed caulk line at the surround can rot a subfloor quietly for years, and nobody sees it until demolition day.

You cannot fully prevent this, but you can plan for it. Ask your installer what they charge for subfloor repair per square foot, and agree it before the job starts. A number agreed in advance is a budget line. The same number quoted on day one with the bathroom in pieces is a negotiation you will lose.

Choosing a door before choosing the entry height

A glass door is the default assumption for a lot of people, and in a low-threshold or barrier-free shower it is frequently the wrong choice. A swinging door reduces the clear entry width, gets in the way of a transfer, and needs a track or a seal at the bottom which partly defeats a flush threshold.

Curtains are not a downgrade in an accessible shower. They move out of the way, they let a caregiver reach in, and they cost a fraction as much. Decide the entry height and who uses the shower first, then decide whether a door still makes sense.

Forgetting the valve is a separate decision

The kit is the pan and the walls. The valve, the trim and the showerhead are usually separate, and they carry their own lead times. We have seen otherwise well-planned jobs held up for three weeks by a fixture on backorder while a complete shower sat in a garage.

Two things to specify deliberately: a pressure-balancing or thermostatic valve, because a hot surge causes a flinch and a flinch causes a fall, and a handheld on a glide bar, because it serves both a standing user and a seated one.

The pre-purchase checklist

Copy this, walk into the bathroom, and fill it in. It takes twenty minutes and it prevents almost everything above.

Measurements

• Width wall to wall at the floor, at hip height, near the ceiling.
• Depth front to back at the same three heights.
• Floor to ceiling, plus soffits, sloped ceilings, fans and lights.

Plumbing

• Drain position: left, right or center, and distance in from the front edge.
• Existing drain line diameter, if you can see it.
• Valve position, and whether it can move.

Structure

• Concrete slab or wood joists.
• Ground floor or above a finished ceiling.
• Anything visible below the bathroom: a basement, a crawl space, a finished room.

Access

• Narrowest doorway from the street to the bathroom.
• Tightest turn, measured as the diagonal.
• Stair width and whether there is a turn or a landing.

People

• Who uses this shower daily, and how are they moving around today.
• Is a shower chair, walker or wheelchair involved now or plausibly in ten years.
• Will anyone need to assist.

Photos

• All four corners of the shower area.
• The plumbing wall.
• The bathroom doorway from the hall.
• The room as a whole.

Questions that come out of these mistakes

How do I find my existing drain line size without opening anything?

If there is a basement or crawl space below, look up at the pipe running from under the tub. If there is not, a plumber can often tell from the trap access or from the age and style of the house. It is a ten-minute question for someone who does it daily, and it is worth asking before you order.

Is it ever right to buy the cheapest kit?

Yes, and we say so on the phone regularly. A rental turnover, a basement bathroom nobody uses, or a house being sold within a couple of years all point to the cheap kit. The mistake is putting one in a primary bathroom for somebody who will still be using it in fifteen years.

Can I reuse my existing valve?

Sometimes, if it is in good condition and in a position that suits the new layout. It is worth replacing anyway if it is not a pressure-balancing or thermostatic type, because a sudden temperature surge causes a flinch and a flinch causes a fall. It is a small line item next to the rest of the job.

How do I tell whether a supplier knows what they are doing?

Ask for the threshold height in inches and what is behind the wall panel. Both questions have a single correct answer and take five seconds to give. Vagueness on either one tells you everything you need.

What if I have already bought the wrong kit?

Call before anything is installed. Stock kits can usually be returned. What cannot be undone is an installed unit, a moved drain, or a wall that was built out to make something fit. The expensive stage begins on install day, not on purchase day.

The pattern behind all seven

Six of these seven mistakes are the same mistake wearing different clothes: deciding what to buy before finding out what the room will allow.

The room has constraints. Where the pipe is. What the floor is made of. How square the walls are. How wide the door is. Who will be using the shower in a decade. Those constraints narrow the field a long way before anyone needs to look at a finish or a price.

Twenty minutes with a tape measure and a flashlight, before you shop, prevents almost every expensive surprise in this article.

And if you would rather just send the numbers to someone and have them tell you what works, that is a service we provide and it does not cost anything.