Bathroom Renovation Plumbing: The Complete Checklist Before You Start

A bathroom renovation is the most complex domestic trade project most homeowners will ever take on. Get the plumbing sequence right and everything flows. Get it wrong and you’re re-tiling over failed waterproofing, re-cutting floors for badly positioned waste pipes, or chasing leaks in a brand-new bathroom.

Here’s the checklist to work through before demolition starts on your bathroom renovation.

Before you buy anything

• Measure your toilet rough-in. That’s the distance from the finished wall behind the toilet to the centre of the waste outlet. Most Australian homes are 140mm (P-trap), but older homes and European-style toilets can differ. Get it wrong and your new toilet won’t fit.
• Confirm your water pressure. Test with a pressure gauge at the laundry tap. Plenty of premium tapware needs 200–350kPa dynamic pressure, so if yours is lower, check with your plumber before you buy.
• Check your hot water system capacity. If the renovation adds a shower or a second bathroom, make sure your hot water system can handle the extra demand.

Before demolition

• Book your plumber for a pre-demolition consult. They need to mark the positions of supply and waste pipes in the walls before anything comes apart.
• Confirm the waste pipe fall. Your plumber has to be sure the floor can take the required fall of 1:60 minimum before the final floor waste position is locked in.
• Identify any shared walls. Pipes running between two bathrooms, or between a bathroom and a bedroom, need careful handling during demolition.
• Plan around the three plumbing stages: rough-in before the walls close, inspection before tiling in some states, and fit-off after tiling.

During rough-in

• Confirm the floor waste position with your tiler before it’s set — once the drain is in and the concrete is poured, moving it gets expensive.
• Set supply stub heights to suit your chosen fixtures, measured off finished floor level rather than the subfloor.
• In some states, including Victoria and Queensland, rough-in work has to be inspected by the relevant authority before the walls are waterproofed and closed.

The waterproofing stage

Waterproofing isn’t plumbing work — it’s done by the tiler or a waterproofing specialist. It’s also the single most important step for preventing leaks. In Australia it must be applied to all wet areas and comply with AS 3740.

Make sure your plumber and waterproofer talk to each other about pipe penetrations. Every pipe coming through a floor or wall has to be sealed as part of the waterproofing application.

After tiling: the fit-off checklist

• All fixtures connect to correctly positioned supply stubs
• Shower mixer set at the right height for the rose and the people using it
• Floor waste accessible and finished with the drain cover you chose
• Every connection pressure-tested before sign-off
• Certificate of compliance issued by your licensed plumber

FAQs about bathroom renovation plumbing

How much of a bathroom renovation does a plumber do?

Your plumber handles all rough-in and fit-off work — everything to do with water supply, waste pipes and fixture connections. The tiler handles waterproofing and tiling, and a builder or carpenter handles structural changes. Getting those trades in the right sequence is what makes a renovation run smoothly.

Can I use the bathroom while the renovation is in progress?

Usually not. Once demolition starts the bathroom is out of service until fit-off is finished. In a single-bathroom household, the two to four week timeline is worth planning around.

Do I need council approval for a bathroom renovation?

Cosmetic renovations — new fixtures in the same positions, same waterproofing envelope — usually don’t need council approval in most Australian states. Structural changes, or adding a bathroom, may require a development application. Check with your council.