Do You Need Waterproofing in a Laundry? WA Requirements Explained

WA laundries with a floor waste must be waterproofed to AS 3740. Learn the rules, common mistakes, and what it costs in Perth.

Is Waterproofing Required in a WA Laundry?

The short answer is: yes, in most cases. Under Australian Standard AS 3740 (Waterproofing of domestic wet areas), any laundry with a floor waste must have waterproofing applied to the floor and up the walls to a specified height. Even laundries without a floor waste are strongly recommended to have waterproofing applied to protect against washing machine leaks, burst hoses, and overflow from sinks and tubs.

Topic	Key Takeaway
Mandatory Compliance	Waterproofing is required by AS 3740 for all WA laundries with a floor waste.
Perth Substrates	Membrane systems must be matched to your specific floor type (concrete vs timber).
Certification	Membranes must be inspected and certified before tiling begins under the Building Act 2011.
Risk Mitigation	Waterproofing is recommended even without a waste to prevent structural damage from leaks.

In Western Australia, the Building Commission WA enforces compliance with AS 3740 as part of the National Construction Code. If you are renovating a laundry in Perth and the work involves removing existing floor tiles, altering plumbing penetrations, or installing a new floor waste, waterproofing is not optional. It must be carried out by a licensed waterproofer, inspected by an independent certifier, and certified before any tiling can begin over the membrane.

What AS 3740 Requires in a Laundry

The standard defines specific zones within a laundry that must be waterproofed, each with minimum coverage requirements. Here is a summary of the key obligations for a typical Perth laundry:

Modern laundry with timber cabinets and tiled splashback representing a compliant wet area renovation

Area	Waterproofing Requirement	Minimum Height
Entire floor (with floor waste)	Mandatory membrane	Floor level, turned up at all junctions
Floor (no floor waste)	Strongly recommended	Floor level, turned up at all junctions
Walls behind laundry tub/sink	Mandatory	150 mm above finished floor level
Walls in shower area (if combined bathroom)	Mandatory	1,800 mm above finished floor level
Junction of floor and walls	Mandatory bond-breaker and membrane	Minimum 30 mm up the wall face
Penetrations (pipes, wastes)	Mandatory puddle flanges and membrane	Sealed around each penetration

Common Waterproofing Mistakes in Perth Laundries

Skipping Waterproofing Because There Is No Floor Waste

Many older Perth homes in suburbs like Morley, Balcatta, and Armadale have laundries without floor wastes. Homeowners sometimes assume this means waterproofing is unnecessary. However, a washing machine failure can release 60 to 100 litres of water onto your floor in minutes. Without a membrane, that water penetrates the concrete slab or timber subfloor and causes structural damage, mould growth, and costly repairs that far exceed the cost of waterproofing. We recommend waterproofing every laundry floor regardless of whether a floor waste is present.

Using the Wrong Membrane for the Substrate

Perth homes sit on a range of substrates: concrete slabs, timber-framed floors with sheet flooring, and compressed fibre cement sheets. Each substrate requires a compatible membrane system. A liquid-applied polyurethane membrane that works perfectly on a rigid concrete slab may crack and fail on a timber floor that flexes under load. Your waterproofer must select a product that is rated and warranted for the specific substrate in your home, and apply it at the correct thickness.

Tiling Before the Membrane Is Inspected

Under the Building Act 2011, a waterproofing membrane in a wet area must be inspected and approved before tiles are laid over it. If your tiler covers the membrane before an inspection takes place, you may be required to remove all tiling at your expense so the membrane can be checked. This is an expensive and completely avoidable mistake that comes down to scheduling the inspection properly within your renovation timeline.

Close up of washing machine hot and cold taps and drain hose in a Perth laundry room

Not Waterproofing Around Penetrations

Every pipe, waste outlet, and fixture that passes through the waterproofed floor or wall needs a puddle flange and a membrane seal. Missing even one penetration creates a path for water to travel beneath the membrane and into the building structure. In Perth homes on concrete slabs, this moisture can wick through the slab and cause efflorescence, cracking, and long-term degradation.

How Waterproofing Fits Into a Laundry Renovation

Waterproofing sits in the middle of your renovation sequence. After demolition, plumbing rough-in, and any wall or floor preparation, the waterproofing membrane is applied and left to cure for the manufacturer’s specified period, typically 24 to 48 hours. Once inspected and certified, tiling proceeds over the top. If you are doing a full laundry renovation in Perth, expect waterproofing to add one to two days to the overall timeline for application, curing, and inspection.

If your laundry shares a wall with a bathroom, coordinating the waterproofing across both rooms at the same time is more efficient and ensures continuous membrane coverage at the shared junction. This is particularly relevant if you are planning a combined bathroom and laundry renovation.

What Does Laundry Waterproofing Cost in Perth?

For a standard laundry of 4 to 6 square metres, waterproofing typically costs between $600 and $1,400 in Perth. The price includes surface preparation, primer application, membrane application in multiple coats, puddle flanges at all penetrations, bond-breaker tape at junctions, and the mandatory inspection certificate. For combined laundry-bathroom spaces, costs are higher because of the larger area and the additional shower zone requirements that demand wall coverage up to 1,800 mm.

James Officer

James Officer, has been renovating homes for more than 20 years. Over a decade ago, James founded Perth Property Improver with a clear vision — to create a reliable, professional service where homeowners could feel confident that their project was in safe hands. Over the years, he has built strong relationships with trusted local contractors, carefully weeding out the average from the excellent, so only the most skilled, dependable tradespeople work on your home.