Bathroom Renovation Plumbing: A Complete Planning Guide

Plumbing is the invisible backbone of every bathroom. Get it wrong, and you'll be ripping up tiles and redoing waterproofing — the most expensive part of any renovation. Get it right, and your bathroom will perform flawlessly for decades.

Here's what you need to know before you start.

1. Understand What's Behind the Walls

Before you plan your new layout, you need to know what's already there. The three critical systems in a bathroom are:

• Water supply — hot and cold lines feeding each fixture
• Waste pipes — the drain lines carrying waste water out, including the sewer connection
• Waterproofing — the membrane behind and under the tiles that prevents water from leaking into the structure

Moving any of these is expensive. The further you move a fixture from its existing plumbing, the more it costs.

2. Plan Your Layout Around the Plumbing

The single biggest cost driver in a bathroom renovation is moving fixtures. If you keep the toilet, basin, and shower in the same positions, your plumbing costs stay low. Move any of them, and you're looking at:

• Rerouting waste pipes (the most expensive — they're large and need correct fall)
• Extending hot and cold water lines
• Adjusting or replacing the waterproofing membrane
• Possibly cutting into structural floor joists to accommodate new waste pipes

If you must move the toilet, try to keep it on the same wall. Moving a toilet to a different wall can add $2,000–$4,000 to the plumbing cost alone.

3. Don't Cut Corners on Waterproofing

Waterproofing is the single most common cause of bathroom failures. A poorly waterproofed bathroom leaks water into the structure, causing timber rot, mould, and damage to ceilings below.

In NSW, waterproofing must be done by a licensed waterproofer and certified to AS 3740. The membrane must cover:

• The entire shower floor and extend up the walls at least 1800mm in the shower area
• The entire bathroom floor if it's timber or particleboard
• All internal corners and joints

Never let a renovator skip or shortcut waterproofing to save time. It's the one thing that will cost you the most if it fails.

4. Choose the Right Fixtures Early

Your plumber needs to know the exact fixtures before roughing in the pipes. The position of the shower waste, the basin mixer, the toilet pan collar — all of these depend on the specific model you choose.

Buy your fixtures before the plumber starts, or at minimum have the exact model numbers and spec sheets ready. Changing fixtures mid-project means redoing pipework.

5. Budget for Plumbing

A typical bathroom renovation plumbing budget includes:

• Rough-in and fit-off (labour): $1,500–$3,000
• Waterproofing: $800–$1,500
• New fixtures (toilet, basin, tapware, shower): $1,000–$3,000
• Moving a waste pipe (per fixture): $500–$1,500

If you're keeping the layout the same, expect the lower end. If you're moving fixtures, budget for the higher end.

6. Use a Licensed Plumber

Bathroom plumbing must be done by a licensed plumber and certified to NSW standards. Unlicensed work won't pass inspection and can void your insurance.

At Tru Blu Plumbing, we handle the full plumbing scope of bathroom renovations — rough-in, waterproofing coordination, fixture installation, and final commissioning. We work with your builder or tiler to keep the project on schedule.

Call 0452 317 892 to discuss your bathroom renovation plumbing.