Kitchen and Bathroom Plumbing: What Gets Involved in a Renovation?

Plumbing is one of the parts of a renovation that most homeowners think about least until something goes wrong with it. The tiles get chosen, the cabinetry gets selected, the benchtop gets ordered, and then somewhere in the middle of it all, the question of what the plumber actually needs to do and when they need to do it becomes very relevant very quickly.

Understanding what's involved in kitchen and bathroom plumbing during a renovation helps you plan properly, ask the right questions and avoid the delays that come from not accounting for plumbing early enough in the process.

Why plumbing has to be planned early

Plumbing work in a renovation isn't something that can be slotted in at any point. It has to happen at specific stages, in a specific sequence, and other trades can't proceed until it's done.

In a bathroom renovation, the plumber does a rough-in by running new pipes and drainage to the correct positions, before waterproofing and tiling begins. The waterproofer can't start until the rough-in is complete. The tiler can't start until waterproofing is done and inspected. The plumber then comes back after tiling to connect the fixtures. That sequence is fixed, and a delay at any stage flows through to everything that follows.

In a kitchen renovation, the plumber needs access before the cabinets are installed to rough in the sink and dishwasher connections. Once the cabinets are in and the benchtop is fitted, the plumber returns to make the final connections.

Getting the plumber booked and briefed early in the renovation planning process, not as an afterthought once everything else is organised, avoids a significant amount of stress.

What a plumber does in a bathroom renovation

The plumbing scope in a bathroom renovation depends on whether the layout is staying the same or changing. Keeping the layout the same is significantly simpler and cheaper. Moving fixtures to new positions requires relocating drainage and water supply lines, which involves more work and more cost.

For a standard bathroom renovation where the layout stays the same, the plumber typically handles:

• Capping off existing supply lines and drainage during the strip-out phase

• Rough-in of new water supply lines to the shower, basin and toilet positions

• Rough-in of new drainage connections

• Pressure testing the rough-in before waterproofing proceeds

• Connection of the shower rose, tapware, basin, toilet and any other fixtures after tiling is complete

• Installation of a new bath if applicable

If the hot water system is being upgraded as part of the renovation, or if a heated towel rail is being added, this is also coordinated at the plumbing stage.

A mandatory building inspection is required in Western Australia after waterproofing is applied and before tiling begins, under the Building Act 2011 (WA). The plumber's rough-in work needs to be completed and the waterproofing applied correctly before this inspection can occur.

What a plumber does in a kitchen renovation

Kitchen plumbing is generally less complex than bathroom plumbing unless the layout is being significantly changed, but it still needs to be done in the right order.

For a standard kitchen renovation, the plumber typically handles:

• Disconnecting and capping the existing sink, dishwasher and any other connections during strip-out

• Rough-in of new supply lines to the sink position, including hot and cold water

• Dishwasher connection point

• Filtered or sparkling water tap connection if applicable

• Waste connection for the sink

• Final connection of the sink, tapware and dishwasher after the benchtop is fitted

If the kitchen involves a gas cooktop, a licensed gas fitter is required to connect or relocate the gas point under the Gas Standards Act 1972 (WA). Some plumbers hold both a plumbing licence and a gas licence. Others hold only one. Confirm this before work starts if gas is involved.

When a layout change is involved

Moving a sink, toilet, shower or bath to a new position involves relocating drainage, which is the most complex and expensive type of plumbing work in a renovation.

Drainage runs at a specific gradient to allow waste to flow correctly. Moving a drainage point, particularly in a slab-on-ground house where the drainage runs beneath the concrete, may require cutting into the slab. This adds cost, time and complexity to the project and needs to be factored into the budget and timeline from the beginning rather than discovered halfway through.

If you're considering a layout change in a bathroom or kitchen, raise it with your plumber before the design is finalised. They can advise on what's possible, what it involves and what it will cost. Making this decision after the cabinetry has been ordered is a significantly more painful experience.

Licensing and compliance requirements for renovation plumbing in WA

All plumbing work in Western Australia must be carried out by a licensed plumber registered with Building and Energy under the Plumbers Licensing Act 1995 (WA).

For most renovation plumbing, the plumber is also required to lodge a Plumbing Notice with Building and Energy before or after the work is completed depending on its nature. This is a legal requirement that confirms the work has been carried out to the required standard. A plumber who doesn't mention this when discussing a renovation job is worth asking about it directly.

Under the Building Regulations 2012 (WA), changes to drainage layout or plumbing configuration that form part of a larger building project may also require a building permit. Your builder or licensed building practitioner can advise on whether this applies to your specific project. The Building and Energy division of DMIRS has plain-English guidance on when building permits are required.

The trades sequencing problem

One of the most common sources of delay in Perth renovations is trades that aren't coordinated properly. The plumber can't complete their rough-in because access hasn't been prepared. The waterproofer turns up before the rough-in is done. The tiler is booked but the inspection hasn't happened yet.

Each of these delays is avoidable with proper planning and a team that understands the sequence. When the renovation work and the plumbing are managed by the same team, the coordination happens internally rather than falling to the homeowner to manage across multiple separate businesses.

This is one of the main reasons homeowners and landlords who've been through a renovation once tend to look for a team that handles multiple trades together the second time around.

What to watch out for in plumbing quotes for renovations

A few things are worth checking when you receive a plumbing quote as part of a renovation.

Is the Plumbing Notice included? Some plumbers quote the labour and materials but charge separately for compliance documentation. Ask whether the Plumbing Notice lodgement is included in the price.

Is the second visit included? Renovation plumbing typically involves at least two site visits — rough-in and final fixture connection. Confirm that both are included in the quote rather than discovering a separate charge later.

What happens if drainage needs to be moved? If there's any possibility the drainage layout will need to change once work starts, ask how this is priced. A variation that involves cutting into a concrete slab is a significant cost that should be discussed upfront.

Who is doing the gas work if applicable? If your kitchen has a gas cooktop, confirm whether the plumber holds a gas licence or whether a separate gas fitter needs to be engaged. This affects both the scope of the quote and the coordination of the work.

This & That manages renovation plumbing across Perth as part of a full renovation service, with licensed plumbers, gas fitters and renovation trades working together under one roof. Visit thisandthat.com.au to find out more, request a quote here or call 0487 606 491 to talk through your renovation plumbing needs.