Bathroom Renovation Plumbing: What You Need to Know Before You Start

Bathroom renovation plumbing in Canberra typically involves three stages: rough-in (moving pipes to new positions), waterproofing (required by ACT building regulations), and fit-off (installing fixtures). The plumbing component of a bathroom renovation usually costs between $3,000 and $8,000 depending on scope, according to industry data from Hipages and ServiceSeeking.

What Are the Three Stages of Bathroom Plumbing?

Every bathroom renovation follows the same plumbing sequence. Understanding these stages helps you plan the timeline and coordinate with your other trades.

Stage 1: Rough-In

The rough-in is where all the pipe work happens. This is done after demolition and before tiling. During this stage, the plumber relocates water supply lines and waste pipes to match the new bathroom layout. If you are keeping everything in the same position, the rough-in is minimal. If you are moving the toilet, adding a double vanity, or relocating the shower, the rough-in becomes more complex and more expensive.

Rough-in work includes installing new hot and cold water supply points, repositioning waste outlets, and connecting to the existing drainage system. In slab-on-ground homes (common in many Canberra suburbs), moving waste pipes may require cutting into the concrete slab, which adds cost and time.

Stage 2: Waterproofing

Waterproofing is not optional. Under the Building Code of Australia and ACT building regulations, all wet areas must be waterproofed to Australian Standards (AS 3740). This includes the shower floor, shower walls to a minimum height, and any area where water could pool or splash.

The plumber typically installs the shower waste and floor waste before the waterproofer applies the membrane. The waterproofing must be inspected and pass before tiling can begin. Getting this wrong leads to leaking showers and water damage to the structure below, which is far more expensive to fix after the fact.

Stage 3: Fit-Off

The fit-off happens after tiling and painting are complete. This is when the plumber installs the visible fixtures: taps, toilet, vanity, showerhead, towel rails, and accessories. It is the final plumbing stage and usually takes half a day to a full day depending on the number of fixtures.

When Should You Book the Plumber in Your Renovation Timeline?

The plumber is one of the first trades you need to engage, even before demolition. Here is why:

1. Before you finalise the design: Talk to your plumber about the layout. Moving a toilet from one wall to another might look simple on a plan, but in practice it can be expensive or even impractical depending on where the existing waste lines run. A 5-minute conversation early on can save you thousands.
2. Demolition day: The plumber needs to cap off water and waste lines before demolition begins to prevent flooding and sewer gas issues.
3. During rough-in: The plumber needs to be on site after demolition to install new pipework before the waterproofer and tiler arrive.
4. Final fit-off: Scheduled after all wet trades (waterproofing, tiling, painting) are complete.

The biggest mistake homeowners make is not booking the plumber early enough. Good plumbers in Canberra are busy, and a renovation that stalls because the plumber cannot get there for two weeks is a costly delay.

What Are the Most Common Plumbing Changes in a Bathroom Renovation?

Here are the most common plumbing modifications and what they involve:

• Moving a toilet: This is one of the most expensive changes because the waste pipe is the largest (100mm diameter) and needs to maintain the correct fall. Moving it more than a metre from its current position often means cutting into the slab. Cost: $800 to $2,500.
• Relocating the shower: Requires new hot and cold supply lines plus a new floor waste. Less complex than moving a toilet but still requires slab work if the waste is moving. Cost: $600 to $1,500.
• Adding a double vanity: If you are going from a single to a double vanity, you need additional water supply points and a wider waste connection. Cost: $400 to $800 for the additional plumbing.
• Installing a freestanding bath: Needs floor-level waste and supply connections that may differ from a built-in bath. Cost: $500 to $1,200.
• Upgrading to a rain showerhead: May require changes to the supply pipe position (from wall-mounted to ceiling-mounted). Cost: $200 to $500.

What Do ACT Waterproofing Regulations Require?

In the ACT, bathroom waterproofing must comply with Australian Standard AS 3740. The key requirements include:

• Shower floors must be waterproofed in their entirety
• Shower walls must be waterproofed to a minimum of 1,800mm above the finished floor level
• The area around the bath must be waterproofed to 150mm above the rim
• Wet area floors outside the shower must be waterproofed with appropriate falls to floor wastes
• All penetrations (pipe holes through the membrane) must be sealed with appropriate flanges

A building certifier must inspect and approve the waterproofing before tiling can proceed. Skipping this step or doing it incorrectly is a common cause of bathroom failures and is not worth the risk.

How Much Does Bathroom Renovation Plumbing Cost?

The plumbing cost depends heavily on how much you are changing. Here is a rough guide based on industry data:

• Like-for-like replacement (same layout, new fixtures): $2,000 to $4,000
• Minor layout changes (moving one or two items, adding a fixture): $3,500 to $6,000
• Major layout change (completely new layout, slab work required): $5,000 to $8,000+

These figures cover the rough-in, waterproofing coordination, and fit-off. Fixtures (taps, toilet, shower) are typically supplied by you or quoted separately.

Should You Use Your Builder's Plumber or Hire Your Own?

If you are using a builder for the overall renovation, they will usually have a plumber they work with regularly. This can be easier for coordination, as the builder manages the scheduling. However, you are not obligated to use the builder's plumber, and there are advantages to hiring your own.

Hiring your own plumber gives you more control over the quality and pricing. You can get multiple quotes and choose someone you are comfortable with. The trade-off is that you take on the responsibility of scheduling around the other trades.

If you are managing the renovation yourself (acting as the owner-builder), you will need to book the plumber directly. Make sure you coordinate timing with your tiler and waterproofer, as the sequence is critical. The plumber must finish the rough-in before waterproofing, and the waterproofing must be complete and inspected before tiling begins.

What Permits and Compliance Are Needed in the ACT?

In the ACT, bathroom renovations that involve plumbing work require compliance with the Building Act. Key requirements include:

• Plumbing permit: Your licensed plumber will lodge plumbing work notices with Access Canberra for any regulated plumbing work
• Building approval: If you are making structural changes or altering the layout significantly, you may need building approval from a certified building assessor
• Waterproofing inspection: Must be completed and signed off before tiling proceeds
• Compliance certificate: Your plumber should provide a compliance certificate upon completion of all plumbing work

Using a licensed plumber ensures all the paperwork is handled correctly. This matters if you ever sell the property, as buyers and their solicitors will want to see that renovation work was done compliantly.

How Can You Keep Bathroom Plumbing Costs Down?

Here are practical tips to manage your bathroom plumbing budget:

1. Keep the layout as close to the original as possible. Every pipe that moves costs money. If you can keep the toilet, shower, and vanity in their current positions, the rough-in cost drops significantly.
2. Choose your fixtures early. The plumber needs to know what you are installing before the rough-in so they can position supply points and wastes correctly. Changing your mind after the rough-in means rework.
3. Buy fixtures yourself. Plumbers mark up the cost of fixtures they supply. Buying your own taps, toilet, and shower from a bathroom supplier can save you money, though check with your plumber first to ensure compatibility.
4. Get multiple quotes. Compare at least three quotes from licensed plumbers. Make sure each quote covers the same scope of work so you are comparing like for like.
5. Do not skip waterproofing. Cutting corners on waterproofing to save money now will cost you far more when the shower starts leaking into the room below.