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Waterproofing and Weatherproofing — The Most Reported Building Defects in NSW

Of all the defects that arise in residential building work, water is the most common culprit. In the Building Commission NSW 2023 Strata Defects Survey, waterproofing was the single most prevalent serious defect — present in 42% of affected apartment buildings. When water enters where it shouldn’t, the consequences compound: damaged finishes, structural deterioration, and disputes that frequently end up before the NSW Civil and Administrative Tribunal (NCAT).

Waterproofing vs Weatherproofing — They Are Not the Same

This distinction matters, and getting it right is part of presenting a defect properly. Waterproofing concerns keeping water in check at wet areas and trafficable surfaces — showers, bathrooms, balconies and decks — governed primarily by AS 3740 (internal wet areas) and AS 4654 (external above-ground). Weatherproofing concerns keeping the weather out of the building envelope — roofs, box gutters, flashings and external walls. Roofing and box gutters fall under weatherproofing, and are governed by the NCC’s weatherproofing provisions and standards such as AS/NZS 3500.3 for roof drainage.

How a "Major Defect" Is Established

An alleged defect only becomes a defect when it can be tied to a breach. A well-prepared expert report traces the pathway from the ground up: a breach of an Australian Standard, which is called up by a clause of the NCC, which exists to satisfy a Performance Requirement of the NCC, which in turn breaches the statutory warranties under the Home Building Act 1989 — and, depending on its nature, may meet the definition of a major defect under section 18E.

The Most Common Water-Related Defects

Bathroom and wet area defects — failed waterproofing membranes, insufficient floor falls, ponding water, absent puddle flanges, and non-compliant waterstops.
Balcony and deck defects — leaks into rooms below, ponding water, efflorescence, inadequate parapet detailing, and inadequate membrane terminations at thresholds and parapets/hobs.
Roof and box gutter defects — overflowing box gutters, incorrect overflows, inadequate rainheads, inadequate box gutter detailing, gutters discharging back into the building, and non-compliant drainage design.
The legal picture — when a waterproofing failure amounts to a major defect under the Home Building Act 1989, and what that means for your matter.

Where to From Here

If you are dealing with a water-related defect — whether you are a homeowner who has been told “it’s normal,”, a band-aid fix (epoxy grout), or a builder responding to an allegation — the starting point is understanding whether the work actually breaches the relevant standard, the NCC, and ultimately the Home Building Act. The pages in this section explain each of the most common defects, how they are identified, and how they are assessed.

RESOURCE HUB

Bathroom and Wet area Defects

Discuss Your Matter

Speak directly with a building expert about the specifics of your dispute — the defects, the standards, and where you sit in the NCAT process.