TL;DR
- New flooring laid over an active leak, a failing toilet seal, or a slow drain problem will need to come up again — often within months. Fix the plumbing first.
- The checks that matter most: hidden leaks under existing floors, toilet pan collar condition, flexible hose age, drain flow in every wet area, and pipe condition in any wall or slab you’re opening.
- Older Sydney homes — anything built before the mid-1980s — carry a higher risk of finding corroded pipes, clay drain lines, and past water damage once the floor comes up.
- Get a plumber in before the flooring contractor, not after. The sequencing matters.
New flooring is one of the more satisfying upgrades you can make to a home. It changes how a room feels immediately. But it also permanently covers everything underneath — pipes, drains, subfloor framing, and any moisture that’s sitting there quietly doing damage.
The mistake people make is treating the flooring job and the plumbing as separate decisions. They’re not. If there’s a slow leak under your bathroom floor, a toilet seal that’s been weeping for two years, or a drain that’s been sluggish since the previous owners moved out, laying new flooring over the top doesn’t fix any of it. It just makes it harder and more expensive to deal with later.
Here’s what to check — and fix — before the flooring goes down.
Run the Water Meter Test Before Anything Else
Before you pull up a single board or tile, do a two-minute check at your water meter. Turn off every tap, appliance, and fixture in the house, then watch the meter dial. If it’s moving, water is going somewhere it shouldn’t be.
This test won’t tell you exactly where the leak is, but it tells you whether there’s an active one. If the dial is moving, you need a plumber before the flooring contractor. There’s no point laying new floors over an unresolved leak.
If you want the full process, this post on what a moving water meter actually means walks through the isolation test step by step.
Check 1: The Bathroom Floor — The Highest-Risk Room
Bathrooms produce more pre-flooring plumbing problems than any other room. The combination of water, steam, tile grout, silicone seals, and fixtures that see daily use means things fail gradually and quietly.
The toilet pan collar
This is the seal between the toilet pan and the drain pipe in the floor. When it fails, wastewater seeps under the pan with every flush — slowly saturating the subfloor and surrounding framing. By the time you notice a soft spot or a smell, the damage is often significant.
Before new flooring goes in, the toilet needs to come off the floor anyway (to allow for proper installation around the base). That’s the moment to inspect the collar and replace it if there’s any sign of deterioration, staining, or movement. Don’t reuse a questionable seal and cover it with new tiles.
The shower drain and floor waste
A shower drain that’s been slow for months isn’t just inconvenient — it’s a sign the drain body, the trap, or the pipe below may have a partial blockage or a structural problem. Clear it and confirm it’s flowing freely before new waterproofing and tiles go on top.
Also check the drain grate and drain body for cracking or movement. A loose drain in a tiled shower floor is a common source of leaks that travel down to the ceiling below.
Waterproofing and the membrane under the existing tiles
If you’re retiling a bathroom, the old waterproofing membrane comes off with the tiles. That means a new membrane must go on before any new tiles or flooring. But before the waterproofer arrives, a plumber needs to confirm there are no active leaks from the supply lines, drain connections, or shower fitting behind the wall that would undermine the new membrane from day one.
Check 2: Under the Kitchen Sink and Around Appliances
Kitchen floors take a long time to replace, which is exactly why plumbing problems under the sink or behind appliances tend to go unnoticed for years. A slow drip from a P-trap connection or a flexible hose that’s been weeping at the fitting will quietly soak into particleboard cabinetry and the subfloor beneath it.
Before new kitchen flooring goes down:
- Open the sink cabinet and look carefully at the P-trap connections and the flexible supply hoses. Feel for moisture on the cabinet base. Press on it — if it’s soft, there’s damage underneath.
- Check the flexible hoses behind the dishwasher and the cold water connection to the fridge (if it has a water dispenser). These hoses have a limited service life and are a common source of slow leaks.
- Pull the dishwasher out if you can and look at the floor underneath. Warping, discolouration, or a musty smell are all signs of a water problem that needs to be resolved before the new floor goes in.
Flexible hoses are worth a specific mention. They’re one of the most common causes of sudden, serious water damage in Sydney homes — and they’re cheap to replace before they fail. If yours are more than ten years old, replace them now while the floor is up. It’s a straightforward job for a licensed plumber.
Check 3: The Laundry
Laundry floors take more water abuse than most people realise. The washing machine hoses, the tub waste, the floor drain, and the hot and cold supply taps all live in a small space that often doesn’t get much attention.
Check the washing machine tap valves — they seize over time and can’t be turned off in an emergency. If the handles are stiff or won’t move fully, replace them before the floor goes in. Check the hoses connecting the machine to the wall taps; if they’re rubber and showing any cracking or swelling at the fittings, replace them.
The floor waste in a laundry is also worth running water through before the new floor goes down. If it drains slowly, clear it. A blocked laundry floor waste during a heavy wash cycle means water on the floor — and water on a brand-new floor you just paid to install.
Check 4: Pipes in Any Wall or Slab You’re Opening
If the flooring job involves lifting a concrete slab, cutting into a screed, or opening a wall cavity, that’s an opportunity you don’t want to waste. Once those surfaces close back up, whatever’s inside them stays there for another decade or more.
This is especially true in older Sydney homes, where galvanised steel supply pipes and clay sewer lines are still common. Galvanised pipe corrodes from the inside, restricting flow and eventually failing at joints. Clay sewer lines crack, sag, and let tree roots in. Neither problem gets better with time — and both become significantly more expensive to deal with once new flooring is in place.
If you’re opening up a wet area floor in a home built before the mid-1980s, ask a plumber to assess what’s exposed before it closes back up. The cost of that conversation is nothing compared to the cost of pulling up new tiles twelve months later.
For more on what older Sydney homes tend to hide under the surface, this post on what’s inside the walls of an older Sydney terrace covers the pipe materials and failure patterns worth knowing about.
Check 5: Look for Signs of Past Water Damage in the Existing Floor
Before the old flooring comes up, look at it carefully. The surface often tells you what’s been happening underneath.
- Soft spots or bounce when you walk across the floor — especially near the toilet, bath, or under the sink — point to subfloor damage from sustained moisture exposure.
- Tiles that have cracked repeatedly or grout joints that keep opening up can indicate movement in the subfloor caused by water damage to the framing below.
- Warped or swollen boards near fixtures or appliances.
- Discolouration or staining on the underside of vinyl or linoleum when you lift a corner.
- A persistent musty smell in a room that should be dry.
Any of these signs means the source of moisture needs to be identified and fixed before the new floor goes in. Laying new flooring over water-damaged framing without fixing the cause just repeats the problem on a fresh surface.
Check 6: Drain Flow Across the Whole House
A flooring renovation is a good moment to check that every drain in the house is flowing properly — not because slow drains are directly a flooring issue, but because a blockage that develops after new flooring is installed can sometimes require access through the floor to fix.
Run water in every basin, shower, bath, and laundry tub and watch how quickly it drains. Anything that’s sluggish is worth clearing or investigating before the floor goes down. If multiple fixtures are draining slowly at the same time, that usually points to a problem further down the line — the main drain or the sewer connection — rather than individual fixture blockages.
A recurring blockage that keeps coming back after clearing is a different problem again. That usually means a structural issue in the drain pipe — a crack, a root intrusion, or a section that’s lost its fall. A CCTV drain inspection is the only reliable way to confirm what’s going on, and it’s worth doing before new flooring covers access points.
Check 7: Isolation Valves — Know Where They Are and Confirm They Work
This one doesn’t get mentioned enough. Before new flooring goes in, locate every isolation valve in the rooms being renovated and test that each one actually closes. Isolation valves seize up when they’re not used regularly — and a valve that won’t close in an emergency is no valve at all.
Under bathroom and kitchen sinks, behind the toilet cistern, at the washing machine wall taps, and at the hot water system — test them all. If any won’t turn or won’t fully stop the flow, replace them while the floor is accessible. It’s a small job that matters a lot if something goes wrong after the renovation is finished.
The Sequencing That Actually Protects Your Investment
The right order for any flooring renovation that touches a wet area is:
- Plumber inspects and fixes any active leaks, drain issues, or failing seals.
- Old flooring and tiles come up.
- Plumber assesses exposed pipes and subfloor framing — fixes anything that needs doing while it’s accessible.
- Waterproofing goes on (in wet areas).
- New flooring or tiles go down.
- Plumber returns for fit-off — reconnecting fixtures, resetting the toilet, replacing tap fittings.
The most common sequencing mistake is skipping step one and three, then discovering a problem partway through step five. At that point, the new floor has to come back up, the waterproofing has to be redone, and the job costs significantly more than it would have if the plumbing had been checked first.
What to Do Before the Flooring Contractor Arrives
You don’t need to know exactly what’s wrong before calling a plumber — that’s what the inspection is for. But it helps to have a clear picture of what you’re planning: which rooms are getting new floors, whether any walls are coming down, whether you’re retiling a wet area or just replacing timber or vinyl in a dry space.
A licensed plumber can walk through the space, run the water meter test, check the drains, look at the fixtures and hoses, and give you a clear picture of what needs to be dealt with before the floor goes down. That conversation is much cheaper than pulling up new flooring six months later.
If you’re in Sydney and want someone to check the plumbing before your flooring job starts, call us or get in touch online. We’ll tell you what needs doing and what can wait — no vague tradie talk, just a straight answer.