Bathtub to Shower Conversion in Singapore: What Is Under the Tub and What Decides the Price

Pictured above: a finished bathroom from our project archive (140BB, an HDB maisonette). A built-in bath, tiled on the outside, with a wall-mounted mixer. The tiled box around a tub like this one comes out first when the tub is replaced with a shower, and the floor underneath it is what this article is about.

A bathtub that nobody has used in years takes up the best part of the bathroom. Taking it out and putting in a shower looks like a subtraction: remove one thing, tile the gap. In practice the tub has been hiding part of your floor, part of your walls and its own drain, and none of that can be seen, measured or tested until the tub and the tiled box around it are hacked out.

That is why the quote has to say what happens to the things nobody can see yet. This guide covers what is under and around a tub, where the shower and its drain go, what the waterproofing has to cover and what to ask for in writing. It uses only figures that we already publish on this site. Anything specific to your bathroom is agreed after a site visit.

The short answer

Treat it as a bathroom floor job, not a fitting swap. Once the tub is gone, the area it covered becomes floor that gets wet every day, and that floor has to fall to a drain, be waterproofed and pass a ponding test before anything is tiled on it. Three things decide the price: where the shower and its floor trap end up, what the hacking finds under and around the tub, and how much of the bathroom is re-tiled so that the result looks like one room and not a patch.

Keep the tub or take it out?

This part is a household decision and no builder should make it for you. Three questions are worth answering honestly before you ask for a quote:

• Who uses it, and is there another bath or shower in the home? If a baby or toddler is bathed in it, or it is your only bathroom, that is a good reason to keep it for now. If it has become a place to park the laundry basket, it is not earning its floor space.
• Is the tub the only thing stopping a comfortable shower? A shower over a tub means stepping over the rim. For someone with a stiff knee, or an elderly parent, that step can be the real problem. Our guide to renovating for elderly parents covers the wider picture.
• Is the bathroom already due for a redo? If the tiles are hollow or the room is twenty years old, a tub removal is a sensible moment to do the whole floor properly, because the hacking is happening anyway.

What is under and around the tub

A built-in tub sits inside a tiled box, and the box sits on the floor slab. Three things are hidden behind and beneath it:

• The tub's own waste outlet. A tub drains through its own outlet, separate from the floor trap elsewhere in the room. When the tub goes, that pipe either has to be reused or closed off properly. A pipe that is left half-sealed under new tiles is a future leak.
• The floor under it. The surface under a tub was never meant to be seen or walked on, so it may sit at a different level from the rest of the room and may not fall towards any drain. Nobody knows until it is opened.
• The lower part of the wall. The wall tiles may stop where the tub rim was, or may never have been laid behind the tub at all. Either way the wall has to be finished down to the new floor.

Our guide to renovating just one bathroom notes that the floor trap and the pipe penetrations are where most old bathrooms actually fail. A tub adds one more pipe to that list.

Where the shower goes, and where the water goes

There are two ways to lay it out, and they do not cost the same.

1. The shower goes where the tub was. The area is clear and the water supply is close, but there is probably no floor trap at that end of the room. A new trap has to be fitted, the floor re-screeded to fall towards it, and the SP and SW pipes may have to be re-routed within the screed, which our bathroom page describes as part of repositioning a toilet, shower or sink.
2. The shower stays where it is and the tub area becomes something else. A cabinet, a washing area or just floor. The existing trap and fall may already suit the shower, so less is moved, but the tub's waste outlet still has to be dealt with and the area it covered has to be re-floored.

Whichever you choose, the floor has to fall to the trap. Our bathroom page states the figure we work to: hack down to the slab, re-screed to a 1:80 gradient and replace the floor trap, rather than skimming over the old surface. That is roughly 1.25 cm of fall for every metre. A tub holds water in a basin; a shower floor has to send it away, and if the new floor is level, or falls the wrong way, you find out the first time someone showers. Our guide to mould, floor slope and the exhaust fan shows what a wrong fall looks like afterwards.

Getting that fall can raise the finished floor level, which moves the door, the threshold and the height of the screen. Ask about it at the site visit, before the tiles are chosen.

The waterproofing covers the whole floor, not just the gap

It is tempting to think that only the patch where the tub stood needs new waterproofing. Our published specification for a bathroom reads differently: two coats of approved waterproofing membrane on the full floor and 1.5m up the wet walls, then a mandatory 24-hour ponding test before any tiling begins. Once the tub is out, the whole floor is a shower floor and takes water, so ask for the whole floor to be covered. A patch of new membrane beside old membrane leaves a joint, and a joint is the kind of place where a leak starts.

The ponding test is a full day in which nothing visible happens, and nobody should offer to save you that day. Someone should look at the ceiling of the unit below while the floor is flooded, not just at your own floor. We explain the test in our guide to toilet waterproofing and the ponding test. If the unit below already has a stain, see who is responsible for a ceiling leak first.

Condo or HDB flat: approvals first

• Condo. Our bathroom page states that condos require MCST approval before bathroom hacking and plumbing work, that common conditions include working hours, a deposit and noise restrictions, and that we coordinate the application with your management office. Ask the office for its renovation requirements before you book anyone.
• HDB flat. Our bathroom page states that bathroom hacking, plumbing alteration and electrical works need an HDB renovation permit, which we file as the licensed contractor (HB-09-5667H). We advise on where the shower can go at the site visit, so have the layout checked before you commit to a plan.

What it costs, and what it does not

We do not publish a price for converting a tub to a shower, and we are not going to make one up. The ranges on our bathroom renovation page are for a full bathroom hack-and-retile with new fittings: $5,000 to $12,000 for an HDB bathroom, $8,000 to $20,000 for a condo bathroom and $10,000 to $25,000+ for a landed bathroom. They tell you the scale of a bathroom job. They are not a quotation for this one, because your number depends on where the trap goes, how much pipework moves, what the hacking finds, how much of the wet wall is re-tiled, the screen and fittings you choose, and how the tub leaves the unit.

How long the bathroom is out of use

Our bathroom page gives a typical bathroom remodel as 2 to 4 weeks per bathroom: hacking on days 1 to 2, plumbing and electrical re-routing on days 3 to 5, waterproofing on day 6, the 24-hour ponding test on days 7 to 8, floor screed and tiling on days 9 to 14, then sanitaryware, fittings, ceiling and handover out to about day 20. Whether taking out a tub changes that outline for your bathroom is something to have written down at the visit, and if the flat has only one bathroom, say so then.

Seven lines the quote should name

Our quotations itemise the waterproofing, tile cost, sanitaryware, accessories and labour separately. For a tub conversion, check that the quote names each of these:

1. Hacking out the tub and its tiled surround, and how the tub leaves the unit.
2. What happens to the tub's waste outlet: reused, re-routed or closed off, and how a closed opening is waterproofed.
3. The new floor trap, where it sits and the fall to it (the figure we publish is 1:80).
4. The waterproofing: two coats, full floor and 1.5m up the wet walls, with the ponding test as its own line. We document the test and provide photos at handover.
5. The tiling extent: which walls, and to what height. Floor-to-ceiling tiling is standard in our scope.
6. The screen, mixer and shower set, by named model.
7. What happens if the hacking finds something unexpected: how it is priced and agreed before the work continues. Put it in writing as a variation order; see our guide to variation orders.

Our guide to comparing bathroom quotations line by line shows where a cheap quote saves its money.

What to do this week

1. Take four photos: the whole room from the door, the tub and its surround, the floor trap, and any stain on the ceiling of the unit below.
2. Decide who uses the tub, and whether you want a screen or an open walk-in shower. Note where the floor trap is, and how far it is from the tub.
3. Ask each contractor to answer the seven lines above, and compare the answers, not just the totals.

We are an HDB Licensed Renovation Contractor, HB-09-5667H. Thinking of replacing a bathtub with a shower? WhatsApp us on 9107 2601 with your property type, your estate and the four photos above, and we will arrange a site visit. Any price depends on that visit. Full scope and pricing for bathrooms is on our bathroom renovation page.

Related reading: the ponding test before any tile goes down · renovating just one bathroom · bathroom quotations line by line · variation orders: changing your mind mid-job