The question comes up most often in houses built for a family half the size of the one living in them now. Three or four bedrooms, one bathroom, and a queue outside it every morning.
A client at Figtree put it better than I could. She said she did not want a nicer bathroom, she wanted a second door. That is the whole brief, really, and it is a good one.
What I have learned pricing these is that the room is never the hard part. You can nearly always find the space. What decides whether a second bathroom is a straightforward few weeks or a small renovation is something nobody thinks about when they are looking at the floor plan, which is where the water goes once it leaves the fixture.
Drainage decides it, not the floor plan
Waste runs on gravity. It needs fall, a consistent one, all the way from each fixture to where it joins the existing line, and in a house on a slab or with a low subfloor there is not much vertical room to play with.
That single constraint explains most of what follows. A new bathroom hard against the existing wet-area wall is cheap because the connection is short and the fall is easy. The same bathroom on the other side of the house means running a new line under the floor for its whole length, and either the floor comes up or, on a slab, you are cutting and re-pouring a channel through it.
So the first thing we do on these jobs is not measure the room. It is find the existing waste line and work out what can reach it. Where the sewer connection sits in the yard matters too, because it sets the direction everything has to head.
Three spots tend to work, in rough order of cost. Backing onto the existing bathroom or the laundry, which is the easy one. Directly above or below the existing bathroom in a two storey house, where the stack is already vertical and in the right place. Then anywhere else, which is a real job.
None of that means the far corner is impossible. It means it should be priced knowing why it costs what it does, rather than as a surprise once the floor is open.
Finding the space without wrecking the house
Where the room comes from is the other half of it, and the options are more limited than a magazine would have you believe.
The end of a hallway is the underrated one. A lot of post-war Illawarra houses have a hall that runs further than it needs to, and capping it with a small bathroom costs you circulation rather than a room. A built-in robe wall is the other. Robes are usually about the right depth already and they back onto a bedroom you were not going to use that strip of anyway.
Borrowing from a bedroom works and is the most common answer, but it is worth being honest about what you are left with. The bedroom has to keep its window and enough floor to still be a bedroom. If the ensuite turns a three bedroom house into a two bedroom house, that is a resale conversation, not just a comfort one, and I would rather have it at the sketch stage than after.
Under the stairs almost never works, for the reason above. There is rarely fall available and the head height goes exactly where you need to stand.
On the size question, people consistently overestimate. A shower, toilet and small vanity in a line down one wall fits into a narrower room than you would guess. What cannot be squeezed is the door swing and the clear space in front of each fixture, so the shape you can borrow matters more than the area. A cavity slider buys back the floor a swing door was stealing, and in a small wet room it is nearly always worth it.
The parts that are not negotiable
Two things on these jobs are not places to save money.
Waterproofing is the first. It is invisible when it is finished, it is the only thing keeping water out of the floor structure and the wall behind it, and it has to be applied properly and left to cure before anything is tiled over it. That curing time is a real gap in the program, and it is the step that gets squeezed when an owner is sequencing their own trades and the tiler is only free on Thursday. The requirements sit under NCC 2025 Volume Two. A failed wet area does not announce itself for a couple of years and then costs far more than the renovation did.
Ventilation is the second, and in a bathroom with no window it is the whole ballgame. An ensuite carved out of the middle of a house has no external wall to put a window in, so the extraction has to be designed rather than assumed, and it has to actually discharge outside rather than into the roof space. Venting a shower into your own ceiling is a slow way of growing mould in the roof.
The plumbing has to be done by a licensed plumber and certified, and the general licensing and consumer side of renovation work is covered on NSW Fair Trading's building and renovating pages.
Approval, and why it is not exempt
Adding a bathroom means new plumbing and usually some change to the layout, so it is not exempt development in NSW. It runs as a complying development certificate or a development application depending on the work, and your certifier or council confirms which. CDC vs DA in NSW explains what actually differs between the two paths.
If the new bathroom involves taking out a wall that turns out to be carrying something, that is its own piece of work with an engineer attached, which I have covered in removing a load-bearing wall.
Worth doing at the same time
If the existing bathroom is also tired, price both together before you decide to stage them.
The wet-area trades come through once instead of twice, the waterproofing and tiling happen as one sequence, and the drainage work you are already doing for the new room is usually the same work that would let you improve the old one. It is the same argument as renovating the kitchen and bathroom together, and it holds up better here because the two rooms genuinely share plumbing.
The counter-argument is living through it. Doing both at once in a one bathroom house means no bathroom at all for a stretch, which is fine if you have somewhere to go and miserable if you do not. We have staged plenty of these deliberately so the new one is finished and working before the old one comes out, which costs a bit more in return visits and is worth it for a family staying put.
The Figtree job ended up as an ensuite off the main bedroom, borrowed from an oversized robe, backing onto the existing bathroom wall so the plumbing barely had to move. About three weeks on site. She got her second door.
If you are weighing up where one could go at your place, that is a site visit and a look under the floor rather than a phone conversation. Call 0434 037 851 or use the contact page. Our bathroom renovations page covers how we run the build, and what a bathroom costs in 2026 is the honest starting point on budget.
Common questions
- Where is the cheapest place to put a second bathroom?
- Against the existing wet-area wall, or directly above or below the existing bathroom. The further the new fixtures sit from the current waste line, the more floor has to come up to run new drainage at the right fall, and that work is usually a bigger line than the tiling and the fittings. A bathroom that backs onto the laundry or the existing bathroom is almost always the cheapest one to build.
- How much space do you need for an ensuite?
- Less than most people assume, if the layout is drawn for the actual dimensions rather than around stock fittings. A shower, a toilet and a small vanity in a line along one wall works in a surprisingly narrow room. What you cannot compromise is the door swing and the clear space in front of each fixture, so the constraint is usually the shape of what you can borrow rather than its area.
- Can you take space from a bedroom for an ensuite?
- Usually, and it is the most common way one gets added. The catch is what the bedroom is left with. A bedroom needs to keep a window and enough floor to still function as a bedroom, and if borrowing the space turns a three bedroom house into a two bedroom house with an ensuite, that is a decision about resale as much as comfort. A built-in robe wall or the end of a hallway is often the better donor.
- Does adding a bathroom need council approval?
- Adding a new bathroom involves new plumbing and usually structural or layout changes, so it is not exempt development in NSW. It runs as a complying development certificate through a private certifier or a development application through council depending on the work, and your certifier or council confirms which applies. The plumbing work itself must also be done by a licensed plumber and certified.
- How long does it take to add an ensuite?
- On site, a straightforward ensuite against existing plumbing is usually a few weeks rather than a few months, because the sequence is fixed: rough-in, waterproofing that has to cure before tiling, tiling, then fit-off. What stretches it is drainage that has to travel, a floor that has to come up, or waiting on a fixture that was ordered late. Lead time on tapware and screens catches more jobs than site work does.
Want a hand with this at your place? Get a free quote or call 0434 037 851.