Bathroom Renovations: The Plumbing Side of Things
A professional plumber working on a bathroom renovation ensures the hidden plumbing infrastructure is done right.
Renovating a bathroom is exciting, but it's crucial to pay attention to the plumbing behind the scenes. Poor plumbing work can lead to leaks, water damage, or costly repairs down the track. This guide will walk you through key plumbing considerations for a bathroom renovation – from choosing a licensed plumber and proper waterproofing, to preparing for the plumber’s visit and understanding how plumbing work differs for concrete slabs versus raised floors. Whether you're simply gathering info or planning to hire a plumber, these tips will help the average homeowner ensure their bathroom reno goes as smoothly as possible.
Verify Your Plumber Is Licensed
Always hire a licensed plumber for any bathroom renovation work. Plumbing is a licensed trade, and using an unlicensed handyman or friend might save a little money upfront but can cause big problems later. Unlicensed work often means no compliance certificate is issued and increases the risk of hidden leaks or poor installations. In fact, insurance claims can be rejected if plumbing work was done by an unlicensed person. This could leave you footing the bill for water damage that a proper plumber would have prevented.
A licensed plumber brings the right qualifications and must meet strict standards. For example, Australian plumbing codes (like AS/NZS 3500) specify how bathroom plumbing must be done safely. If work doesn’t adhere to these standards, you could face health hazards (e.g. incorrect hot water settings causing scalding) and costly fixes. Moreover, if something fails, your home insurance might not cover the damage if the plumbing wasn’t done by a qualified professional. It’s just not worth the risk.
How can you check your plumber’s license? In Victoria, for instance, you can use the Victorian Building Authority (VBA) online register to verify that a plumber is registered and licensed for the class of work required. All licensed plumbers carry a photo ID card listing the types of plumbing work they are authorized to perform – don’t hesitate to ask to see it. Similar license check services exist in other states (for example, NSW has a public license lookup). Taking a minute to verify credentials will give you peace of mind that your renovation is in capable hands.
Waterproofing: Protect Your Bathroom from Water Damage
One of the most critical aspects of a bathroom renovation is waterproofing. Bathrooms generate a lot of moisture, especially in showers, and without proper waterproofing you risk serious damage. If water sneaks into the wrong places – behind tiles or under floors – it can rot structural timber, cause mold and mildew, create bad odors, and even impact your health. Water might not show up right away on the surface, but over time it can seep through tile grout lines or tiny cracks, leading to hidden damage. That’s why simply relying on tiles or a coat of waterproof paint isn’t enough – you need a dedicated waterproofing membrane system under the tiles.
A properly waterproofed bathroom ensures longevity and prevents nightmare scenarios like leaks into adjacent rooms or ceilings below. Remember, tile and grout are not waterproof on their own; they are somewhat porous and can let water through. So during your renovation, a waterproofer (often a certified specialist or the tiler with the right qualifications) will apply a membrane on the floor, shower base, and up the walls before any tiling is done. In Australia, waterproofing in wet areas is so important that it’s classified as a structural element – failures are considered structural defects, underscoring how critical it is to get it right. Skipping or botching the waterproofing is one of the costliest renovation mistakes, often resulting in having to rip up tiles and redo the job.
What can you do? Ensure your plumber/builder uses a licensed waterproofer or is certified to do the waterproofing. They should use the correct membrane products and follow the applicable standard (AS 3740 for waterproofing wet areas). Key spots like corners, wall-to-floor joints, and pipe penetrations must be thoroughly sealed. Don’t be shy to ask your tradesperson about how they will waterproof the shower and tub areas – a true professional will be happy to explain their process. Ultimately, good waterproofing protects your home from leaks and moisture issues, saving you from expensive repairs and giving you a bathroom that stands the test of time.
Tiled Showers and the Importance of Water Stops
A beautiful tiled shower is often the centerpiece of a bathroom reno – but it's not just about looks. Correct installation of a tiled shower is vital for function and preventing leaks. One common oversight is drainage slope: the shower floor must be properly sloped toward the waste outlet. If the slope (fall) is too shallow or the drain is poorly positioned, water will pool on the floor instead of flowing away. Showers placed far from the existing drain, or without adequate fall, can lead to slow drainage and annoying standing water. Always ensure your plumber and tiler coordinate to get the drain location and floor gradient right. Additionally, all fixtures (shower, basin, toilet) need proper venting and trap design – things a licensed plumber will account for so you don’t get gurgling drains or sewer smells later.
Another critical element in showers is the water stop. If you haven’t heard this term, a water stop is basically a barrier (often a small hob or an aluminum angle embedded at the shower threshold) that keeps water within the wet area. In Australia, water stops are typically installed around the perimeter of the shower base and at the entry of any walk-in shower or wet area doorways. They are tied into the waterproofing system. The idea is that if any water sneaks under the tiles (for example, through grout or a minor crack), the water stop will “stop” it from travelling to the rest of the bathroom floor or into the building structure. Instead, the water is directed back towards the shower drain (often via a puddle flange that connects the waterproof membrane into the waste trap).
Why are water stops so important? Without a proper water stop, water that escapes the immediate shower area can seep under adjacent floor tiles, causing damp patches, warping timber subfloors, or dripping to the level below. Over time this leads to rot and mold in places you can’t see until the damage is severe. A well-installed water stop, combined with correct waterproofing, ensures that your shower water stays in the shower. It also helps prevent those little rivulets of water from escaping the shower onto your bathroom floor where they could cause slip hazards. Australian standards mandate water stops for domestic bathrooms, so make sure your renovation includes this detail. When your tiler builds the shower, you'll either have a curb (hob) or a flush strip at the threshold – both serve as water stops. The bottom line: a correctly built, tiled shower with proper slope and water stopping will protect your bathroom from future leaks and give you a worry-free experience.
Preparing for the Plumber’s Rough-In Work
To keep your project running smoothly (and avoid extra charges), it pays to prepare before the plumber arrives for the rough-in stage. "Rough-in" is when the plumber runs new water supply lines and drain pipes in the walls or floor before everything is closed up and tiled. As the homeowner, your job is to make sure the plumber has all the info they need to do the job right the first time. Here are some steps to get ready:
Plan your layout and choose fixtures early. Ideally, you should know exactly where your toilet, shower, bath, and vanity will go before rough-in. Last-minute changes to fixture locations can be costly, especially if pipes have already been laid. If you can keep new fixtures close to the original plumbing layout, you'll save money – moving pipes around is complex and expensive. For instance, shifting a toilet even a small distance means moving the big waste pipe; if the bathroom is on a concrete slab, that might involve jackhammering the slab. So, finalize your layout and discuss it with your plumber in advance.
Have all your fittings and fixtures on hand (or at least selected). This includes tapware (faucets, shower heads, mixers), the toilet suite, the vanity (and what kind of basin it uses), the bathtub, and any specialty items like a wall niche or shower mixer diverter. The plumber doesn't need the physical items on day one, but they do need the specifications. Different fixtures have different requirements – for example, a wall-hung vanity might need the drain positioned at a certain height, or a freestanding tub filler may require plumbing coming up from the floor. If you supply the spec sheets to your plumber ahead of time, they can rough in the pipes at the correct positions and avoid having to redo work later. This prevents the scenario of “Oops, the vanity drain is 5cm off-center for the sink” which could incur extra charges to fix.
Clear the work area and prepare the site. Remove any personal items, and if it’s a renovation (not a new build), typically demolition of the old bathroom will happen before the plumber does rough-in. Make sure any old fixtures that are being replaced (toilet, tub, etc.) are removed or that the plumber knows whether they are removing them. If you’re doing a DIY demolition, have it done and all debris cleared out so the plumber has space to work. Also, ensure the plumber has easy access to the water shut-off for the bathroom (they’ll likely need to turn off water during the rough-in).
Communicate special requests. If you have any non-standard ideas (like a rain-head shower coming from the ceiling, or multiple shower heads, or a bidet spray, etc.), let the plumber know upfront. These can usually be accommodated, but they might require extra plumbing lines or fittings. The earlier you discuss it, the easier it is to include in the rough-in. Good communication will help avoid miscommunication that could otherwise lead to rework later on.
By preparing in these ways, you help the plumbing rough-in go quicker and prevent costly changes down the road. Your plumber will be able to set up all the pipes confidently, and other trades (tilers, electricians, etc.) can follow on schedule.
Plumbing Work: Concrete Slab vs. Raised-Floor Homes
Not all homes are built the same, and the type of foundation your house has will affect how the plumbing work is done in a bathroom remodel. Generally, houses either have a concrete slab foundation or a raised floor (stumps or footings) with a crawl space. Each presents different challenges for moving or adding plumbing:
Homes on a concrete slab: All the plumbing pipes are encased in or beneath the concrete. This means if you need to move a drain (for example, relocate a toilet or shower waste), the plumber must cut into the slab to access and re-route the pipe. This is labor-intensive – typically done by cutting channels in the concrete with a saw and jackhammering it out. When a house is first built, the plumbing layout is set before the slab is poured, so making changes later requires literally going through solid concrete. It’s certainly doable, but it takes time, special tools, and adds cost. For instance, adding a new toilet on a slab where there wasn’t one will involve careful planning of the waste run, likely trenching the slab, then re-pouring concrete over the new pipes. Because of this, minor changes can become major work on a slab – even moving a toilet a short distance can be expensive since both the inlet (water) and outlet (sewer) pipes have to be adjusted in the slab. If you’re on a slab, try to stick to the existing drain locations as much as possible, or be prepared for the extra work. A good plumber will plan the shortest and best route for any new pipes to minimize how much concrete needs cutting.
Homes on stumps or raised foundations: These have a crawl space or void under the floor, which usually makes plumbing modifications easier. The plumber can go under the house to add or move pipes without cutting through concrete. Moving a waste pipe or running a new line is a matter of threading it through the subfloor framing. However, don’t underestimate it – even on a raised floor, moving a toilet or shower still requires reworking pipes within walls and floors, and can be costly. The difference is largely that you won’t need concrete cutting. Plumbers will still need to ensure there’s enough slope for new waste pipes under the floor and that the new pipes can tie into the existing sewer line properly. In some cases, space or structural obstacles under older houses can make the job tricky, but generally a timber floor gives more flexibility for plumbing changes than a slab.
Bottom line: Know what type of foundation you have, and consult with your plumber about what’s feasible. If you plan to change the bathroom layout significantly on a slab, expect a higher cost and a longer timeline due to the concrete work. On the other hand, if your house is on a raised foundation, take advantage of that flexibility – you might be able to move fixtures a bit more easily, but still weigh the benefit against the cost. Always ensure any abandoned pipes are properly sealed and any new cuts (in concrete or wood framing) are done safely and in accordance with building codes. With the right approach (and a skilled plumber), even big changes like relocating a shower or adding a new bath drain can be accomplished in either type of home – it's just a matter of planning, effort, and budget.
Final Thoughts
A successful bathroom renovation isn’t just about picking beautiful tiles and fixtures – it also hinges on solid plumbing work. By hiring a licensed plumber, you protect yourself and your home, knowing the work meets code and won’t void your insurance. By insisting on proper waterproofing and water stops, you safeguard your new bathroom from leaks and moisture damage. And by planning ahead and coordinating with your plumber, you can avoid common pitfalls and keep the project running smoothly. Renovating a bathroom is a team effort between you and your tradespeople. When you take these steps – checking credentials, prepping the site, communicating your plans – you empower your plumber to do their best work. The result will be a bathroom that not only looks great on the surface but is also reliable and watertight behind the walls. Now, armed with this plumbing-side knowledge, you can approach your bathroom reno with confidence and look forward to enjoying your new space without any unwelcome surprises down the line. Happy renovating!