Waterproofing defects in new homes — how to identify them and what to do

Waterproofing failures are the single most common major defect in Australian new builds, and they are among the most expensive to fix because by the time they become visible, water has usually already caused damage behind walls and under floors. If you know what to look for — and where to look — you can identify a waterproofing problem early, document it correctly, and enforce your rights under the statutory warranty before the damage compounds.

Why waterproofing fails in new builds

Most waterproofing failures are not caused by a single catastrophic error. They result from a combination of small shortcuts, sequencing mistakes, and inadequate supervision during construction. The most common causes are:

Incorrect membrane application. Liquid-applied waterproofing membranes must be applied to a minimum thickness and allowed to cure fully before tiling begins. When trades are under schedule pressure, membranes are applied too thin, coverage is inconsistent at junctions and corners, or tiling begins before the membrane has cured — bonding tiles to an incompletely formed membrane rather than to the substrate underneath.

Inadequate treatment at junctions. The junctions between floors and walls, around penetrations such as floor wastes and pipes, and at the base of shower screens and bath hobs are the highest-risk points. The NCC (National Construction Code) and AS 3740 (Waterproofing of domestic wet areas) both require specific treatment at these junctions — typically a coved fillet or flexible sealant. When these are missed or rushed, water finds the path of least resistance.

Wrong product for the location. Not all waterproofing products are suitable for all locations. A membrane rated for interior use may not be appropriate for an exposed balcony. Using an interior membrane on a balcony that experiences UV, foot traffic, and thermal movement is a common defect in multi-storey homes and apartments.

Inadequate preparation of the substrate. If the concrete or screed substrate is uneven, has sharp edges, or contains contamination (dust, oil, residue from previous trades), the membrane may not adhere correctly. This leads to delamination — the membrane lifts away from the substrate and water bypasses it entirely.

Drainage falls that are incorrect or reversed. Even a correctly installed membrane cannot compensate for water that pools in a wet area rather than draining away. AS 3740 requires shower floors to drain to the floor waste and not retain standing water. Falls that are too shallow or, in some cases, actually slope away from the drain send water toward the walls and junction points.

Where to look: the high-risk areas in every new home

Waterproofing is required by the NCC and AS 3740 in any “wet area” — any room or space where water is used or drained. In a typical new home that includes:

Showers and bathroom floors. The most common location for waterproofing failures. The floor and walls of a shower enclosure must be waterproofed to a minimum height (300mm up the wall for showers, 150mm in adjoining areas under AS 3740). The waterproofing must extend under the shower screen base and be continuous to the floor waste.

Bath surrounds. The area around a freestanding or built-in bath requires waterproofing under AS 3740 — this is regularly missed or installed incorrectly, particularly where the bath meets the wall.

Laundries. Floor waterproofing is required in laundries. Failures here are common because laundry defects are often inspected less carefully at handover than bathroom defects.

Balconies, terraces, and podium decks. External waterproofing is subject to greater thermal movement and UV degradation than internal wet areas. Balcony waterproofing failures are classified as major defects in all Australian states because water penetrating a balcony typically tracks down into the structure below.

Roof and roof penetrations. The roof membrane, sarking, and flashings around any penetrations (vents, skylights, solar systems, stacks) are a frequent source of water ingress. Flashings that are incorrectly lapped, undersized, or not properly sealed at penetrations allow water to enter the wall cavity.

Windows and door frames. Incorrect or missing flashings above window and door openings cause water to track down the cavity and appear as internal water staining or damp walls remote from the original entry point — which makes the source harder to identify.

Visible signs: what to photograph at handover and during the defects liability period

Many waterproofing failures are not immediately visible at handover — they emerge over the first weeks and months after the home is occupied and wet areas are in regular use. However, some indicators are visible at or shortly after handover:

Grout cracking and missing grout. Grout cracks at joints — particularly at the junctions between floor and wall tiles — are a significant indicator. Grout is not a waterproofing material. If the membrane beneath is moving or the substrate was not properly prepared, the grout will crack and open a direct water path. Photograph the full length of every floor-to-wall junction in wet areas.

Efflorescence. White or greyish salt deposits on tiles, grout, brickwork, or render are caused by water moving through a substrate and depositing dissolved salts on the surface as it evaporates. Efflorescence on internal tile grout or on external brickwork adjacent to a wet area is a reliable indicator of water movement behind or through the surface.

Water staining. Discolouration on walls or ceilings adjacent to wet areas — often a brown or yellowish shadow stain — indicates water has penetrated and is tracking along framing or substrate materials. Water staining on the ceiling below a bathroom is a particularly urgent sign. Photograph these from multiple angles in good light.

Bubbling, blistering, or peeling paint. Paint that bubbles away from its substrate or blisters without physical impact has moisture underneath it. This is common on walls adjacent to showers or on ceilings below wet areas. Photograph the full extent of any bubbling or peeling, not just the worst spot.

Swelling or lifting skirting boards and floor materials. Timber skirting boards and engineered timber flooring are highly sensitive to moisture. Skirtings that are bowing outward from the wall base, lifting at the floor junction, or showing visible moisture staining at their base are a strong indicator of water migration out of a wet area. Floor materials — particularly in the room immediately adjacent to a bathroom or laundry — that are cupping, lifting, or separating at joints indicate moisture from below.

Hollow or loose tiles. Tap every tile in a wet area with a hard object (a pen lid works). A hollow sound indicates the tile is not properly bedded — there is an air gap under the tile that will eventually allow water to move freely. In a wet area, hollow tiles are a waterproofing risk, not just a cosmetic issue.

Rust staining. Orange rust staining at floor wastes, grout joints, or around fixings indicates prolonged water contact with ferrous materials — water is sitting in these locations longer than it should.

Hidden signs: what you cannot see but can infer

Some waterproofing failures are not visible at all without invasive testing. If you notice any of the visible signs above, it is worth commissioning a professional building inspector to conduct:

• Flood testing — plugging floor wastes and filling wet areas to a specified water level for a set period (typically 24 hours) to test whether the membrane holds
• Thermal imaging — infrared scanning to identify areas of moisture retention in wall and floor substrates without opening up surfaces
• Moisture meter readings — measuring moisture content in walls adjacent to wet areas, which can identify active water movement not yet visible at the surface

These tests are particularly important on balconies, where water penetrating the slab is often invisible from above but visible as staining or efflorescence on the soffit or balcony edge below.

What AS 3740 actually requires

AS 3740:2010 (Waterproofing of domestic wet areas) is the Australian Standard that sets the minimum requirements for waterproofing in new residential construction. It is called up by the NCC and is therefore mandatory, not advisory.

Key requirements under AS 3740 include:

• Shower floors and walls must be waterproofed to a minimum height of 1,500mm above the floor on the shower walls, or to the full height of the wall if the ceiling is lower
• Areas adjacent to showers (outside the enclosure) must be waterproofed to 150mm above the floor on vertical surfaces and across the full floor area of the wet zone
• Floor wastes must be waterproofed at the penetration point — the membrane must be turned into and bonded to the drain body
• All junctions (floor-to-wall, wall-to-wall inside a shower, at the threshold of a shower screen) must receive a coved fillet of waterproofing material or be treated with flexible sealant
• Balconies must be waterproofed across the full surface area, with the membrane turned up at perimeter edges and all penetrations sealed

When documenting a waterproofing defect, referencing AS 3740 specifically — and identifying which clause has not been met — significantly strengthens your defect notice.

Defects liability period versus statutory warranty for waterproofing

These two protections are different in scope and duration, and it matters which one applies to your situation.

The defects liability period (DLP) begins at practical completion (handover) and typically runs for 13 weeks to 12 months depending on your contract and state. During the DLP, your builder is obligated to return and rectify defects that were not apparent at handover. The DLP applies to all defects, including waterproofing.

The statutory warranty for waterproofing extends well beyond the DLP. Waterproofing failures are classified as major defects in all Australian states, which means they attract the longer statutory warranty period:

These are approximate. Check your specific state legislation and your contract.

The practical implication: even if you miss your DLP because you didn’t notice a waterproofing problem until 18 months after handover, you may still have valid statutory warranty rights. The key is notifying your builder in writing as soon as you discover the defect.

What “major defect” means for waterproofing under state legislation

In most Australian states, a “major defect” is defined as a defect in a structural element or a defect that is likely to render the building or a part of it uninhabitable, or threatens structural integrity, or is likely to result in loss of use of the building for its intended purpose.

Waterproofing explicitly sits within this definition — most state legislation, including the NSW Home Building Act 1989 and the Queensland QBCC Act, specifically names waterproofing of wet areas as a major defect category. This is important for two reasons:

1. It attracts the longer warranty period regardless of how the defect presents — even a waterproofing failure that appears minor at first (a small stain, slightly bubbling paint) is legally a major defect because of the category it falls into, not the extent of visible damage at the time of discovery.

2. It may qualify the home for a claim against home warranty insurance if the builder is insolvent, has died, or has had their licence suspended — because home warranty insurance in most states only covers major defects.

The HIA (Housing Industry Association) and QBCC both publish guidance on what constitutes a major defect for waterproofing. If your builder disputes the categorisation, these are the reference points to cite.

How to document waterproofing defects

Documentation is where most homeowner warranty claims succeed or fail. A builder, building authority mediator, or tribunal member needs to be able to understand the defect from your record alone, without visiting the property.

For each waterproofing defect, record:

1. Location — precisely. “Main bathroom, floor-to-wall junction on the east wall of the shower, from the drain to the corner, approximately 900mm” is useful. “Shower” is not.

2. What you can see. Describe the visible sign — grout cracking, efflorescence, water staining, bubbling paint, swelling skirting — as neutrally as possible. Do not interpret; describe.

3. Photographs — multiple. A wide shot showing the location in context. A close shot showing the defect itself. If the defect has measurable dimensions (a crack, a stain), include a ruler or coin in the frame for scale. Photograph in good natural or artificial light — flash-only photographs of dark grout lines rarely show the defect clearly.

4. Date of discovery. This establishes where you are in the warranty timeline.

5. Any prior communication with the builder. If you raised this verbally first, note the date and who you spoke to. Follow up in writing regardless.

Checka makes this process systematic — photograph, describe, tag the location, and your defect record is timestamped and exportable as a report your builder, certifier, or tribunal can use directly.

How to formally notify your builder

The most important step after documenting a waterproofing defect is notifying your builder in writing. Verbal notification is not sufficient — if the matter escalates to a tribunal, you need to be able to show that the builder was informed and given a reasonable opportunity to rectify.

Your written notice should:

• Identify the specific location of each defect
• Describe what is visible
• Reference AS 3740 and the NCC where the defect represents a non-compliance
• Reference your statutory warranty rights under your state’s relevant legislation
• State a reasonable rectification timeframe (14 days is appropriate for most waterproofing defects; immediate response for anything causing active water damage to the structure or contents)
• Request written confirmation of when the builder intends to inspect and rectify

Send the notice to your builder’s registered business email address and keep a copy of the sent email. If your builder has a defects management process, use it — but also send a direct email to your contract contact so there is no ambiguity.

If your builder does not respond within the stated timeframe, or disputes that a defect exists, you can escalate to your state building authority:

• QLD: QBCC — lodge a complaint at qbcc.qld.gov.au
• NSW: NSW Fair Trading — fairtrading.nsw.gov.au
• VIC: Domestic Building Dispute Resolution Victoria (DBDRV) — dbdrv.vic.gov.au
• WA: Building Commission WA — buildingcommission.wa.gov.au

Key takeaways

• Waterproofing failures are the most common major defect in Australian new builds and are classified as major defects in all states, attracting warranty periods of 6–10 years
• AS 3740 sets the minimum waterproofing standard for domestic wet areas — any departure from it is a non-compliance, not just a workmanship issue
• Key visual signs to photograph include grout cracking at junctions, efflorescence, water staining, bubbling paint, swelling skirtings, and hollow tiles
• Document every defect with precise location, description, and dated photographs — vague descriptions are difficult to enforce
• Notify your builder in writing as soon as a defect is discovered, referencing AS 3740 and your statutory warranty rights by name
• If your builder disputes the defect or fails to respond, escalate to QBCC, NSW Fair Trading, DBDRV, or the relevant state authority — most offer free dispute resolution before tribunal proceedings