TL;DR
- Removing a bath and fitting a walk-in shower is not just a demolition and tiling job. The drain position, drain size, waste pipe fall, water supply height, and waterproofing all need to be addressed before a single tile goes on.
- The biggest plumbing variable is the drain. A bath drain sits at one end of the tub; a shower drain usually sits in the centre or at the lowest point of the floor. Moving it means working under the slab or subfloor — and that changes the scope significantly depending on your floor type.
- All plumbing work in this conversion must be done by a licensed plumber in NSW. Waterproofing must also be done by a licensed waterproofer. These are not optional steps.
- The job is very achievable in most Sydney homes. The key is knowing what you’re getting into before the bath comes out.
Why this conversion is more than a cosmetic change
Most people picture the job as: pull out the bath, tile the floor, put in a shower screen. That’s the visible part. The plumbing underneath is a different story.
A bathtub and a walk-in shower use the same space but handle water in fundamentally different ways. A bath fills up and drains slowly through a waste at one end. A shower delivers a continuous flow of water directly onto a tiled floor and needs to drain fast, from wherever the floor falls to. Those two things require different drain positions, different pipe sizes in some cases, and a completely different approach to waterproofing.
Get the plumbing right and the conversion lasts decades. Get it wrong and you’re looking at damp subfloors, mould behind tiles, and a repair bill that dwarfs the original job.
Here’s what actually changes.
Change 1: The drain position
This is the biggest variable in the whole job, and it’s the one most people don’t think about until the bath is already out.
A bathtub drain is typically at one end of the tub, close to the wall. A walk-in shower drain needs to sit at the lowest point of the shower floor — usually somewhere near the centre of the space, or along one edge depending on the floor gradient design. In most conversions, those two positions don’t line up.
Moving the drain means a plumber needs to access the waste pipe underneath the floor and extend or redirect it to the new position. How hard that is depends entirely on what your floor is made of.
Timber subfloor (most pre-1980s Sydney homes)
Accessing the waste pipe under a timber subfloor is usually straightforward. A plumber can get under the floor from a crawl space or by lifting boards, reposition the drain outlet, and adjust the pipe fall. It adds time to the job but it’s not a major drama.
Concrete slab (most post-1980s builds and ground-floor apartments)
This is where drain repositioning gets more involved. The waste pipe is encased in concrete. Moving the drain means cutting into the slab, rerouting the pipe, and making good afterwards. It’s a legitimate part of the job — not a rare complication — but it adds cost and time, and it needs to be factored into the plan before demolition starts.
In some cases, a plumber can design the shower floor gradient to fall toward the existing drain position, avoiding the need to move it at all. That’s worth discussing before you commit to a layout.
Change 2: The drain size
A bathtub typically drains through a 40mm waste pipe. Showers — particularly walk-in designs with larger shower heads or rainfall heads — benefit from a 50mm drain to handle the flow rate properly. If your existing waste pipe is undersized for the shower you’re planning, the plumber will need to upsize it as part of the repositioning work.
A slow-draining shower floor isn’t just annoying. It means water is sitting on the tiles longer than it should, putting extra pressure on your waterproofing and grout. Getting the drain size right from the start avoids that problem entirely.
Change 3: The water supply lines
A bath usually has a mixer or tap set positioned low on the wall — close to the tub rim — because that’s where you fill the bath from. A walk-in shower needs the mixer valve positioned higher on the wall, at a comfortable operating height, with the shower head above that.
In most conversions, the existing supply lines can be extended or rerouted to the new valve position. The plumber will cap off the old bath spout connections, relocate the mixing valve to the correct height, and run supply to the shower head position. If you’re adding a rail shower, a fixed overhead head, or multiple outlets, each of those needs to be planned at the rough-in stage — before the walls are closed up.
This is also the point where the plumber checks whether your existing hot and cold supply lines are in good enough condition to reuse, or whether sections need replacing. Older Sydney homes with galvanised supply pipes often reveal corrosion at this stage that’s worth sorting while the wall is open.
Change 4: The floor level and shower base
A walk-in shower floor needs to fall toward the drain. The required fall under AS/NZS 3500 is typically around 1:60 to 1:80 — enough to move water to the drain without creating a slope you can feel underfoot.
In a conversion, achieving that fall usually means screeding the floor to the correct gradient before waterproofing and tiling. If the existing bathroom floor is already tiled, those tiles come up. The substrate underneath gets assessed, screeded to the correct fall, and then waterproofed before anything goes back on.
If the subfloor underneath is damaged — from years of moisture around the bath — that damage needs to be repaired before the screed goes down. It’s one of those things you can’t know for certain until the bath is out and the floor is exposed.
Change 5: Waterproofing — the step that decides everything
This is where a lot of budget conversions fall apart. Waterproofing a shower is not the same as waterproofing a bath surround. A shower floor and the lower walls of the shower recess need to be waterproofed to a membrane standard that complies with the National Construction Code — applied to the prepared substrate, cured properly, and inspected before tiling starts.
In NSW, waterproofing in wet areas must be done by a licensed waterproofer. It’s not a job for a tiler with a tin of membrane, and it’s not something you can inspect by looking at the finished tiles. The membrane goes on before the tiles, and if it’s wrong, you won’t know until moisture has been working its way into the subfloor for months.
A proper conversion treats waterproofing as a non-negotiable step, not an afterthought. Make sure whoever is managing your job has a licensed waterproofer confirmed before demolition starts.
Change 6: The floor waste gully
Under NSW plumbing requirements, a floor waste is required in shower areas. This is the drain fitting in the shower floor that connects to the waste pipe below. It needs to be the right size for your drain pipe, correctly positioned at the low point of the floor, and installed with the correct trap depth to prevent sewer gases from entering the bathroom.
If you’re repositioning the drain, the floor waste goes in at the new location as part of the rough-in. If you’re keeping the drain in roughly the same position, the existing floor waste may be reusable — but the plumber will check the trap and seal condition before signing off on it.
The approval question
Most bath-to-shower conversions in NSW are considered exempt development and don’t require council approval. The work doesn’t change the footprint of the building or alter any structural elements.
That said, the plumbing work itself still requires a licensed plumber, and a Certificate of Compliance (also called a compliance certificate) must be issued after the work is complete. This is the document that confirms the plumbing was done to the required standard. Keep it — you’ll need it if you ever sell the property or make an insurance claim related to the bathroom.
If you’re in a strata building, there’s an extra step. Most strata schemes require you to notify the owners corporation before carrying out any work that involves waterproofing or changes to plumbing. Some require written approval. Check your strata by-laws before you start, and factor in the approval timeline. Doing the work without notifying strata can create liability issues if something goes wrong later.
What the job sequence actually looks like
Understanding the order of work helps you plan the timeline and avoid the most common mistakes.
- Plumbing rough-in first. Before any tiling, screeding, or waterproofing, the plumber repositions the drain, adjusts the waste pipe, and relocates the supply lines to the new valve and shower head positions. The walls and floor are open at this stage.
- Floor screed. Once the drain is in the right position, the floor is screeded to the correct fall. This needs to cure before waterproofing goes on.
- Waterproofing. The licensed waterproofer applies membrane to the floor and lower walls of the shower recess. This also needs curing time — typically 24 to 48 hours minimum, sometimes longer depending on the product and conditions.
- Tiling. Once waterproofing is cured and inspected, tiling can begin.
- Plumbing fit-off. The plumber returns to install the shower mixer, shower head, and any other fixtures once tiling is complete. This is also when the shower screen or frameless glass is fitted.
- Certificate of Compliance. The plumber issues the compliance certificate once the work is inspected and signed off.
Rushing any of these steps — particularly waterproofing cure time — is how conversions fail. A job that takes five to seven days done properly can look identical on day one to a job that was rushed through in three. The difference shows up two years later.
What the job uncovers in older Sydney homes
Older Sydney homes — anything built before the 1980s — tend to have a few things behind the bathroom walls that aren’t obvious until the bath comes out.
- Galvanised supply pipes. These corrode from the inside over decades. If the pipes serving the bathroom are galvanised, the conversion is a good opportunity to repipe that section in copper or PEX while the wall is open.
- Damaged substrate. Years of moisture around a bath can soften timber framing and deteriorate the wall sheeting behind tiles. Any damaged material needs to come out and be replaced before waterproofing goes on.
- Undersized or poorly graded waste pipes. Older drainage in Sydney was often laid in clay or early PVC. If the existing waste pipe is in poor condition or incorrectly graded, the plumber will flag it during rough-in.
None of these are reasons not to do the conversion. They’re reasons to get a proper assessment before you lock in a budget, so you’re not surprised halfway through the job.
One thing worth thinking about before you commit
If your home has only one bathroom and it contains the only bath, removing it can affect resale value — particularly if your home is likely to appeal to families with young children. It’s not a reason to keep a bath you don’t use, but it’s worth thinking through before demolition day.
If you do want to keep the option open, some conversions are designed to accommodate a freestanding bath in the same space as a walk-in shower. That’s a more involved job, but it’s possible in bathrooms with enough floor area. Worth raising with your plumber at the planning stage.
What you can’t do yourself in NSW
To be clear: the plumbing work in a bath-to-shower conversion is not a DIY job in NSW. Repositioning a drain, rerouting supply lines, adjusting waste pipe falls, and installing a new shower valve all require a licensed plumber. Waterproofing requires a licensed waterproofer. Doing this work without a licence voids your home insurance cover for any related water damage and can create problems when you sell.
What you can do yourself: help clear the space before the plumber arrives, remove personal items from the bathroom, and make sure there’s clear access to the work area. That’s genuinely useful and costs nothing.
For a broader look at what happens to your plumbing during a bathroom renovation, the bathroom plumbing upgrades guide covers the full picture — from keeping the existing layout versus moving fixtures, to what compliance documents you should have when the job is done.
Ready to get it sorted?
If you’re planning a bath-to-shower conversion in a Sydney home and want a straight answer on what the plumbing will actually involve, get in touch with Jasco Plumbing. Bill or one of his licensed plumbers will look at the bathroom, tell you what needs to move, and give you a fixed price before any work starts. No vague estimates, no surprises on the invoice.
Call us, book online, or tell us what you’re planning and we’ll take it from there.