The 10 Waterproofing Defects NSW Keeps Finding in New Apartments (NCC 2022 and 2025)
Building Commission NSW lists ten waterproofing defects its auditors keep finding on apartment sites. Here is each one with its NCC 2025 and NCC 2022 clause and when to catch it, plus the new NCC 2025 balcony rules and a floor fall calculator.
Building Commission NSW audits apartment buildings while they are going up, and a small group of defects keeps turning up. It publishes them as the Building Defects Library: 40 defects across waterproofing, fire safety, structure, building enclosure and services, each with the clauses it breaches.
This series takes the Library one building element at a time and adds what the Library leaves out: the NCC 2025 clause beside the NCC 2022 one it was written against, the point in construction where each defect is cheapest to catch, and what to keep as evidence. Part 1 is waterproofing, the most commonly reported serious defect in NSW apartment buildings.
In one minute
Waterproofing is the most commonly reported serious defect in NSW apartment buildings, reported in 44% of the 520 buildings in the 2025 strata survey, and more of it surfaces as buildings age.
The Library lists ten waterproofing defects: five on balconies and roofs (AS 4654.2) and five in bathrooms (AS 3740).
NCC 2025 adds Code rules around the balcony defects. F1D4 now requires a fall of at least 1:80 in the slab itself, an overflow at least 20 mm below the inside slab, a 70 mm step down at the door and a 70 mm hob. The membrane details are still AS 4654.2.
The bathroom rules did not change. F2D2 and F2D4 read the same in both editions: falls of 1:80 to 1:50 to the floor waste, and AS 3740 for the rest.
Which edition applies depends on your state and a date. NSW, Queensland, South Australia and Tasmania are on NCC 2022 until 1 May 2027, and the Northern Territory has not adopted NCC 2025.
How common are waterproofing defects in new apartments?
Since 2021, strata managers have been surveyed every two years about serious defects in Class 2 buildings of four or more storeys, a sample chosen to match the six-year statutory warranty for major defects. The 2025 survey, the first led by Building Commission NSW, with Strata Community Association NSW, covered 520 buildings registered from July 2018 to June 2024. Just over half (53%) had at least one serious defect in common property, the same as in 2023 (page 10).
Waterproofing led again, in 44% of buildings. It also keeps growing after handover: among buildings registered in 2018, the share with a waterproofing defect rose from 46% in the 2023 survey to 66% in 2025 (pages 12 and 13). Only 7% of buildings registered in 2024 had reported one, but defects often appear years after occupation, so the report warns that low rates in the newest buildings may not last. Where strata managers knew the cost, serious defects had cost an average of A$215,400 per building (page 4).
Which NCC edition applies to my project?
The Library is written against NCC 2022. NCC 2025 is published nationally but called up by each state on its own date, and the date that decides is usually when the approval is applied for or issued, not when work starts. Your certifier or building surveyor confirms the edition for a project.
| State | In force on 7 November 2026 | NCC 2025 from | The date that decides |
|---|---|---|---|
| NSW | NCC 2022 | 1 May 2027 | Construction certificate application made |
| VIC | NCC 2025 | 1 May 2026 | Building permit issued |
| QLD | NCC 2022 | 1 May 2027 | Building development application approved |
| SA | NCC 2022 | 1 May 2027 | Building consent application made |
| WA | NCC 2025 (NCC 2022 may still be used for permit applications made by 30 April 2027) | 1 May 2026 | Permit application made |
| TAS | NCC 2022 (NCC 2025 applied from 1 May to 4 June 2026) | 1 May 2027 | Certificate of likely compliance issued |
| ACT | Either, chosen per project | Required for approvals from 1 May 2027, unless a DA or works approval was lodged before 1 November 2026 | Building approval determined |
| NT | NCC 2022 | Not adopted | Building permit granted |
The waterproofing clauses below are national. Of them, South Australia has its own versions of F2D2 and F2D4 (and an extra SA F2P3), so SA wet areas are checked against those; check your state's appendix to the NCC for anything else.
What changed for balconies in NCC 2025?
NCC 2022 left most of a balcony's detail to AS 4654.2. NCC 2025 renumbered Part F1 and added Code rules around the balcony defects: where the fall goes, the overflow level, a step down and a hob. The membrane details themselves are still AS 4654.2.
| Requirement | NCC 2022 | NCC 2025 |
|---|---|---|
| Rainwater performance requirement | F1P2, F1P3 | F1P1 |
| Falls, overflow, step down, hob | None (AS 4654.2 covers falls) | F1D4 (new) |
| Concrete substrate and its preparation | None (AS 4654.2 covers preparation) | F1D5 (new) |
| Exposed joints | F1D4 | F1D6, now on a ridge or high point |
| External membranes to AS 4654.1 and AS 4654.2 | F1D5 | F1D7, now laid directly on the structural slab |
| Surface finishes | None | F1D10 (new): self-draining or fixed to the membrane |
| Wet areas to Specification 26 and AS 3740 | F2D2 | F2D2 |
| Floor wastes, falls 1:80 to 1:50 | F2D4 | F2D4 |
The biggest practical change is where the fall goes. Under NCC 2022 the fall could be made in a screed over a flat slab. Under NCC 2025 the structural slab itself must fall at least 1:80 (F1D4(1)(b)); a screed, topping or tile bed does not count except inside a planter box (Note 3), and the membrane goes directly on the slab (F1D7(2)). The fall now has to be designed into the formwork.
The five balcony and roof defects
All five break AS 4654.2:2012, which both editions call up for a roof, balcony, podium or similar horizontal surface.
1. The membrane stops at the outlet
The membrane ends at the edge of the outlet instead of running onto its flange and down into it, so water tracks under the membrane at the drain.
| NCC 2025 | F1P1; F1D7(1)(b); a drainage system to F1D3 (F1D4(1)(a)) |
| NCC 2022 | F1P2 and F1P3; F1D5(1)(b) |
| Standard | AS 4654.2 cl 2.10: turned down into the inlet, or clamped or bonded to a flange; a sump, pit, grate or cage against debris |
| Catch it | At the membrane inspection, before screed or tiles. Photograph every outlet with the membrane lapped in. |
2. The membrane is not turned into the overflow
The overflow is there, but the membrane does not run into it, so water that backs up gets behind the membrane.
| NCC 2025 | F1D4(1)(a): sufficient overflow provision; F1D4 Note 1: its invert at least 20 mm below the adjacent internal floor slab |
| NCC 2022 | F1D5(1)(b); the NCC sets no overflow level |
| Standard | AS 4654.2 cl 2.11: membrane turned into the overflow, and the finished floor must not reduce an outlet's design flow. The Library notes one alternative: a pre-formed overflow outlet with its own flange. |
| Catch it | Set the overflow level before the pour, then check the membrane at it. Record the invert and the inside slab level. |
3. Water ponds on the balcony or roof
The surface holds water instead of draining it to the outlet.
| NCC 2025 | F1D4(1)(b): at least 1:80 in the plane of the structural slab, where a screed does not count (Note 3); F1D7(2): membrane directly on that slab |
| NCC 2022 | F1D5(1)(b) |
| Standard | AS 4654.2 cl 2.5.2: no water retained beyond surface-tension residue; the fall in the slab or a screed over it; its note recommends no flatter than 1:100 |
| Catch it | At the formwork, before the pour. Survey the slab levels before the membrane goes down. |
4. The surface is not ready for the membrane
Protrusions, voids, formwork marks, dust or a wet slab stop a bonded or liquid membrane from adhering.
| NCC 2025 | F1D5: concrete to AS 3600, its surface prepared to suit the membrane under F1D7(1)(b) |
| NCC 2022 | F1D5(1)(b) |
| Standard | AS 4654.2 cl 2.5.1 (a compatible substrate) and cl 2.5.3.1 (smooth, clean, dry, free of dust, with a moisture content that suits the membrane). Partially bonded and unbonded membranes need the same smooth, clean, dry surface (cl 2.5.3.2 and 2.5.3.3); the moisture-content rule is for bonded and liquid membranes. |
| Catch it | Before priming. Keep the moisture reading and the membrane maker's preparation sheet. |
5. The membrane is not terminated at the sliding door
The membrane does not turn up high enough at the door, or there is no sub-sill flashing, so wind-driven water gets under the door.
| NCC 2025 | F1D4(1)(c): at least 70 mm step down from the inside slab to the balcony slab, where applicable. Note 5: the 70 mm is not the membrane's termination height; where AS 4654.2 requires more, the membrane is taken higher. |
| NCC 2022 | F1D5(1)(b); the NCC sets no step down |
| Standard | AS 4654.2 cl 2.8.1.1: the upturn high enough that water, including wind-driven water, cannot flow over it; cl 2.8.3: a sub-sill flashing as part of the membrane system and, where the floor levels allow no upturn, the membrane also fixed under the sill and drained to the stormwater system. The Standard leaves the height to its informative Appendix A, so the Library says the façade engineer should set it. |
| Catch it | Before the door frame goes in. Photograph the upturn and the sub-sill flashing with a tape in shot. |
The five bathroom defects
Bathroom waterproofing did not change between the editions. In a Class 2 or 3 building, F2D2(1) requires wet areas to be water resistant or waterproof under Specification 26 and to comply with AS 3740:2021. For the materials and the shower set-out, see our guides to AS 3740:2021 and waterproof and water-resistant materials.
6. Water ponds on the bathroom floor
The floor outside the shower is too flat, or falls the wrong way, so water sits on it.
| Both editions | F2D4(2): where there is a floor waste, a continuous fall of the floor plane to it of at least 1:80 and no steeper than 1:50. F2D4(1): a bathroom or laundry above a sole-occupancy unit or public space must have one. |
| Standard | AS 3740 accepts 1:100 outside the shower, but the NCC overrules a referenced document where they differ (A4G2), so 1:80 governs. |
| Catch it | Check the falls before tiling, then water test after. |
7. Water ponds in the shower
The shower floor is too flat for water to reach the waste.
| Both editions | F2D2(1); F2D4(2), which also caps the fall at 1:50 |
| Standard | AS 3740 cl 2.3.2: at least 1:80 to the waste in the shower floor finish |
| Catch it | Check the screed falls before the membrane or tiles, depending on the system. |
8. No waterstop at the doorway
There is no waterstop angle at the door, so water on the floor runs under the door and into the next room.
| Both editions | F2D2(1) |
| Standard | AS 3740 cl 4.9.1: a waterstop at every floor-level opening, its vertical leg flush with the finished floor, with the floor membrane sealed to it |
| Catch it | Before the screed and tiles. Photograph each doorway. |
9. The floor waste flange sits proud
The leak control flange (the puddle flange) at the floor waste sits on top of the substrate instead of in a recess, so the membrane cannot run onto it cleanly.
| Both editions | F2D2(1) |
| Standard | AS 3740 cl 4.3.1(b): the leak control flange recessed into the substrate, not above it, and sealed to the riser |
| Catch it | When the plumber sets the risers, before the membrane. |
10. The fillet or bond breaker at the wall is wrong
The junction between the wall and floor has no fillet or bond breaker, or one that does not suit the membrane, so the membrane tears when the junction moves.
| Both editions | F2D2(1) |
| Standard | AS 3740 cl 4.10: a fillet or bond breaker at every change of plane or material, and at movement joints, where the membrane is bonded; Table 4.10 sets the bond breaker's width by the membrane's class |
| Catch it | Before the membrane. Check the class on the membrane's data sheet against the width installed. |
How much fall does a floor need?
Enter the length of the floor in its direction of fall, from the waste or outlet to its high edge. The calculator gives the drop the fall needs, with both editions for a balcony.
When should each defect be caught?
The Library chose defects that can be seen without testing and cost far less to fix during construction than after people move in. Each one has a moment when it is still exposed:
| Stage | Check | Defects |
|---|---|---|
| Formwork, before the pour | Falls and set-downs in the slab, the step down at each door, outlet and overflow positions and levels | 2, 3, 5 |
| Before the membrane | Slab clean and dry, flanges recessed, fillets and bond breakers, waterstops in place | 4, 8, 9, 10 |
| Membrane inspection | Turned into every outlet and overflow, upturns and sub-sill flashings at doors | 1, 2, 5 |
| Before tiling | Falls checked with a level, 1:80 to 1:50 in bathrooms | 3, 6, 7 |
How can AEC Assistant help?
AEC Assistant works from the edition and state of your project, and cites the clauses it relies on.
Before the pour: upload the drawings to a project and ask it to review the balcony and wet-area details. It marks each issue it finds on the sheet, with the clause.
For the site: it builds an inspection and test plan from your specification, with hold points like the ones above.
When a defect is found: it turns site photos and notes into a defect register and drafts the direction notice or defect letter, citing the clause for your edition.
Where to read the source
Building Defects Library, Building Commission NSW, v1.1, June 2025 (written against NCC 2022)
2025 Strata Defects Report, Building Commission NSW with Strata Community Association NSW, November 2025
NCC 2025 Volume One, Parts F1 and F2, and NCC 2022 Volume One with Amendment 2, from the ABCB
AS 4654.2:2012 and AS 3740:2021, from Standards Australia
This is part 1 of five in our rewrite of the Building Defects Library. The others cover fire safety, structure, building enclosure and services, and the series index lists all 40 defects.
Questions this guide answers
Which waterproofing defects does the NSW regulator keep finding?
Building Commission NSW's Building Defects Library lists ten that its auditors find often on apartment sites: on balconies and roofs, a membrane not turned into the outlet or the overflow, ponding, a surface not prepared for the membrane, and a membrane not terminated at the sliding door; in bathrooms, ponding on the floor and in the shower, no waterstop at the doorway, a floor waste flange that is not recessed, and the wrong fillet or bond breaker at the wall junction. Waterproofing defects were reported in 44% of the 520 buildings in the 2025 strata survey.
What fall does a balcony need under NCC 2025?
At least 1:80 in the plane of the structural slab itself (NCC 2025 Volume One F1D4(1)(b)). A screed, topping or tile bed does not count except inside a planter box (F1D4 Note 3), and the membrane goes directly on the slab (F1D7(2)). Under NCC 2022 the membrane follows AS 4654.2, which lets the fall be made in the slab or a screed over it and recommends, in a note, no flatter than 1:100.
What fall does a bathroom floor need?
Where there is a floor waste, the floor plane must fall to it continuously at no less than 1:80 and no more than 1:50 (F2D4(2), the same in NCC 2022 and NCC 2025), the shower included. AS 3740 also requires at least 1:80 in the shower, and accepts 1:100 outside it, but the NCC overrules a referenced document where they differ (A4G2).
Does a balcony need a step down at the door?
Under NCC 2025, yes, where applicable: at least 70 mm from the inside floor slab to the balcony slab (F1D4(1)(c)). That is not the membrane's termination height (F1D4 Note 5): AS 4654.2 requires the upturn to stop wind-driven water, with heights as guidance in its informative Appendix A, and that can mean more than 70 mm. NCC 2022 sets no step down; the termination follows AS 4654.2.
Which NCC edition applies to a project in NSW?
NCC 2022 until NCC 2025 takes effect in NSW on 1 May 2027. The edition is decided by the date the construction certificate application is made, not when work starts, and the certifier confirms it for each project.
