The 6 Building Services Defects NSW Keeps Finding in New Apartments (NCC 2022 and 2025)
Building Commission NSW lists six services defects its auditors keep finding on apartment sites, all in ventilation and ductwork. Here is each one with its NCC 2025 and NCC 2022 clause and when to catch it, plus a natural ventilation calculator.
Building Commission NSW audits apartment buildings while they are under construction, and the same defects keep 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 works through the Library one element at a time and adds what it leaves out: the NCC 2025 clause beside the NCC 2022 one it was written against, the stage of work when each defect is still in view, and what to check. Part 5 of five is building services, and all six of its defects are in ventilation and ductwork.
In one minute
Key services defects were reported in 15% of the 520 buildings in the 2025 strata survey, and in 31% of the buildings registered in 2018, up from 16% two years earlier. The survey's key services also covers plumbing, electrical services, acoustics and lifts, so these are not the shares of buildings with the six defects below.
The Library's six services defects are all ventilation and ductwork: one in the car park, one in the rooms and four in the ducts.
The NCC clauses kept their numbers. NCC 2025 adds AS 1668.4 as a route to natural ventilation, calls up the 2024 edition of AS 1668.2, and its E2D12 no longer names clause 5.5 of AS 1668.1: the system is designed and installed as a car park ventilation system to AS 1668.1.
The duct defects are Standards defects. Both editions call up AS 4254.1:2021 for flexible duct and AS 4254.2:2012 for rigid duct. The Library quotes the 2012 edition of AS 4254.1, whose clause numbers differ.
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 services defects in new apartments?
The 2025 Strata Defects Report, from Building Commission NSW with Strata Community Association NSW, asked strata managers about serious defects in 520 Class 2 buildings of four or more storeys, registered from July 2018 to June 2024. Its "key services" covers mechanical, plumbing and electrical services, acoustics and lifts (page 10), so it is wider than the Library's six. Key services defects were reported in 15% of buildings, close to the 14% of the 2023 survey (page 12).
The age of the building matters more. Among buildings registered in 2018, the share with a reported key services defect rose from 16% in the 2023 survey to 31% in 2025, an increase the report calls significant (pages 12 and 13). It reads this as defects coming to light as buildings age, so the low rates in the newest buildings may not last.
Which NCC edition applies to my project?
The Library was written against NCC 2022. Each state calls up NCC 2025 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 each 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 |
Only one clause below has state variations. NSW replaces F6D6 in both editions to delete the reference to AS/NZS 3666.1, the microbial control Standard for air-handling and water systems, because NSW regulates that under its Public Health Act 2010. NCC 2022 also has a South Australian F6D6, which adds an option for storage sheds and grain stores. E2D12, F6D7, F6D8, F8D4, S7C5 and J6D7 have no state variations in either edition.
What changed for services in NCC 2025?
Very little. Every clause below has the same number in both editions, and the ductwork Standards are the same editions. Three changes matter: F6D6 accepts natural ventilation designed to AS 1668.4 as well as the openings of F6D7; E2D12 no longer names clause 5.5 of AS 1668.1 but has the system designed and installed as a car park ventilation system to AS 1668.1; and NCC 2025 calls up the 2024 editions of AS 1668.2 and AS 1668.4.
| Requirement | NCC 2022 | NCC 2025 |
|---|---|---|
| Outdoor air, odours and contaminated air (performance) | F6P3, F6P4, F6P5 | F6P3, F6P4, F6P5 |
| Ventilation of rooms | F6D6: openings to F6D7, or mechanical to AS 1668.2 | F6D6: adds natural ventilation to AS 1668.4 |
| Openings of 5% of the floor area | F6D7 | F6D7 |
| Ventilation borrowed from an adjoining room | F6D8 | F6D8 |
| Car park ventilation | F6D11; E2D12: clause 5.5 of AS 1668.1 | F6D11; E2D12: designed and installed as a car park ventilation system to AS 1668.1, no clause named |
| Bathroom, toilet, kitchen and laundry exhaust in a Class 2 unit | F8D4 | F8D4 |
| Fire hazard properties of ductwork | S7C5: AS 4254.1 and AS 4254.2 | S7C5 |
| Sealing the ducts of an air-conditioning system of 3,000 L/s or more | J6D7 | J6D7 |
| Ventilation Standards called up | AS 1668.1:2015, AS 1668.2:2012, AS 1668.4:2012 (car parks only) | AS 1668.1:2015, AS 1668.2:2024, AS 1668.4:2024 |
| Ductwork Standards called up | AS 4254.1:2021, AS 4254.2:2012 | AS 4254.1:2021, AS 4254.2:2012 |
The car park and the rooms
The first two defects are in the NCC itself: Part E2 for the car park, Part F6 for the rooms.
1. A jet fan blows onto the sprinklers or detectors
Jet fans, also called impulse fans, push air along a basement car park at high speed. Where a fan is fixed in line with a row of sprinkler heads or smoke and heat detectors, its air stream can interfere with those devices. The Library also points to Fire and Rescue NSW's guideline on impulse fans in car parks.
| NCC 2025 | E2D12: in a Class 7a car park, basement included, with mechanical ventilation to AS 1668.2, the car park ventilation system is designed and installed to AS 1668.1 |
| NCC 2022 | E2D12: the same car park must comply with clause 5.5 of AS 1668.1 |
| Standard | AS 1668.1:2015 cl 5.5.1(a): a jet fan sits midway between the rows of sprinklers and detectors, blowing along the gap between them; cl 5.5.5: it shuts down when fire mode starts or a sprinkler operates |
| Catch it | On the coordinated ceiling plan, before the sprinkler and detector heads go in. Check each fan's position and direction on site, and its shutdown at commissioning. |
2. A room has no ventilation
A room that must be ventilated has neither openings to outside nor a mechanical system: for example an internal study, or a room whose only window is fixed glass. F6D6 covers every room a person occupies for any purpose, bathrooms and laundries included.
| NCC 2025 | F6D6(1): natural ventilation to F6D7 or to AS 1668.4, or mechanical ventilation or air-conditioning to AS 1668.2 and AS/NZS 3666.1 (NSW deletes AS/NZS 3666.1) |
| NCC 2022 | F6D6(1): natural ventilation to F6D7, or mechanical ventilation or air-conditioning to AS 1668.2 and AS/NZS 3666.1 (NSW deletes AS/NZS 3666.1) |
| Both editions | F6D7: openings that can be opened, at least 5% of the floor area; F6D8: borrowed through an adjoining room in the same unit, except for a sanitary compartment; F8D4: in a Class 2 unit, a bathroom or toilet exhaust of at least 25 L/s, discharged to outdoor air, and if it does not run continuously in a room without F6D7 openings, interlocked with the light switch with a 10-minute run-on |
| Standard | AS 1668.2 for mechanical ventilation: the 2012 edition under NCC 2022, the 2024 edition under NCC 2025 |
| Catch it | In the window schedule, before the windows are ordered: the openable area, not the glass area, against each room's floor area. On site, check that every internal room's exhaust is ducted outside. |
The four ductwork defects
The Library cites no NCC clause for these four: they break AS 4254.1 for flexible duct and AS 4254.2 for rigid duct. The NCC calls those Standards up mainly in two places: S7C5, for the fire hazard properties of all ductwork in a Class 2 to 9 building, and J6D7, for sealing the ducts of an air-conditioning system of 3,000 L/s or more. AS 1668.1 also requires the ducts of systems that keep running in a fire to be built and installed to them (clauses 2.3.4 and 2.3.5).
3. A flexible duct joint is not airtight
Flexible duct is pushed onto a collar, taped and banded, and its insulated jacket is then pulled over the joint and taped again. Where the tape is short or creased, the band is missing or the jacket is left open, air leaks into the ceiling space and the jacket no longer seals the insulation.
| Called up by | Both editions: S7C5 calls up only the fire hazard properties of AS 4254.1 and AS 4254.2; J6D7 calls up their sealing for an air-conditioning system of 3,000 L/s or more, except ducts within the only or last room served. Below that, the sealing requirement comes from the mechanical specification. |
| Standard | AS 4254.1:2021 cl 5.2 and 5.4.2: tape or mastic makes the air seal between the duct core and the collar, with the tape applied in at least three overlapping, tensioned wraps; a drawband goes over the seal; the insulation and jacket are pulled over and taped for a vapour seal; leakage must be negligible (cl 5.2.6). The Library quotes cl 2.2.7 of the 2012 edition. |
| Catch it | At the open-ceiling inspection, before the lining goes up. Check every connection and photograph a sample of each type. |
4. The flexible duct has no compliance label
Insulated flexible duct carries a printed label along its jacket. Without it no one can tell on site who made the duct, whether it claims to meet AS 4254.1, or what R-value it has.
| Called up by | Both editions: S7C5 calls up the duct's fire hazard properties under AS 4254.1, not its label; the label shows it is the tested product |
| Standard | AS 4254.1:2021 cl 5.6: the label repeats every 1,000 mm along the duct, stays legible for its service life, has characters at least 10 mm high, and names the manufacturer, conformance with AS 4254.1:2021 and the insulation R-value (cl 2.7 of the 2012 edition the Library quotes) |
| Catch it | On delivery, before the duct goes up. Check the label on each roll and keep a photo with the delivery docket. |
5. Rigid duct joints are not sealed
Sheet metal duct leaks at its joints, seams and penetrations unless they are sealed. How much has to be sealed depends on the static pressure the duct is designed for, so the seal class comes from the mechanical design.
| Both editions | J6D7: in an air-conditioning system of 3,000 L/s or more, ducts outside the only or last room served are sealed to AS 4254.1 and AS 4254.2 for the system's static pressure |
| Standard | AS 4254.2:2012 cl 2.2.1 and Table 2.2.1: openings closed with adhesive, mastic or gaskets, and welds continuous; the seal class rises with the pressure, from the joints and seams near each end of a duct piece up to every joint, seam and duct wall penetration; no pressure until the sealant has cured. Cl 2.2.4: systems of 3,000 L/s or more are tested for leakage. |
| Catch it | Before the duct is insulated and the ceiling closes. Check the sealing against the pressure class on the mechanical drawings, and keep the leakage test records. |
6. A rigid duct is not properly supported
Hangers too far apart, too light or poorly fixed let a duct sag between supports, which strains its joints and seals.
| Called up by | Both editions: S7C5 (fire hazard properties) and, for air-conditioning systems of 3,000 L/s or more, J6D7 call up AS 4254.2; neither edition has a clause of its own on duct supports |
| Standard | AS 4254.2:2012 cl 2.6.1: strap and rod hangers sized and spaced to its tables and fixed to the structure so they keep their load capacity, and where a duct must be fire-rated its rod suspension has the same rating (cl 2.6.1(f)); cl 2.6.2: a wire rope system is a matched, load-tested system installed to its manufacturer's specification; cl 4.1.5: each section between hangers carries its own weight and the loads it was built for |
| Catch it | Before the ceiling closes. Check strap and rod hanger size, spacing and fixings into the slab against the Standard's tables for each duct size, and a wire rope system against its manufacturer's specification. |
How much opening does a room need?
Enter a room's floor area and choose how it gets its air. The calculator gives the openable area F6D7 and F6D8 ask for, the same in NCC 2022 and NCC 2025. For natural light and ventilation room by room, use the light and ventilation calculator.
When should each defect be caught?
Once the ceilings are lined the four duct defects are out of sight, and the jet fan clash is cheapest to fix on paper. Each has a moment when it is still in view:
| Stage | Check | Defects |
|---|---|---|
| Design and coordination | Jet fans midway between the sprinkler and detector rows, the openable area of each window against its room, the pressure class of each duct run | 1, 2, 5 |
| Delivery | A label on every roll of flexible duct | 4 |
| Ceiling open, before lining | Duct joints sealed, flexible connections taped and banded, hangers and fixings, exhausts ducted outside | 2, 3, 5, 6 |
| Commissioning | Jet fans shut down in fire mode, leakage test records, exhaust run-on timers | 1, 2, 5 |
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 services go in: upload the mechanical and fire services drawings to a project and ask it to review the car park ventilation and ductwork. It marks each issue it finds on the sheet, with the clause.
For the site: it builds an inspection and test plan from your mechanical 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 E2, F6, F8 and J6 and Specification 7, and NCC 2022 Volume One with Amendment 2, from the ABCB
AS 1668.1:2015, AS 1668.2:2012 and 2024, AS 1668.4:2024, AS 4254.1:2021 and AS 4254.2:2012, from Standards Australia
This is part 5 of five in our rewrite of the Building Defects Library. The others cover waterproofing, fire safety, structure and building enclosure, and the series index lists all 40 defects.
Questions this guide answers
Which building services defects does the NSW regulator keep finding?
Building Commission NSW's Building Defects Library lists six, all in ventilation and ductwork: a car park jet fan in line with the sprinkler heads or detectors, a room with neither natural nor mechanical ventilation, a flexible duct joint that is not airtight, flexible duct without its compliance label, rigid duct joints not sealed, and rigid duct not properly supported. Key services defects were reported in 15% of the 520 buildings in the 2025 strata survey, but the survey's key services also covers plumbing, electrical services, acoustics and lifts, so that is not the share of buildings with these six defects.
Where does a jet fan go in a car park?
Midway between the rows of sprinklers and detectors, blowing along the gap between them (AS 1668.1:2015 clause 5.5.1(a)), and it shuts down when fire mode starts or a sprinkler operates (clause 5.5.5). The NCC calls this up for a Class 7a car park with mechanical ventilation through E2D12, in NCC 2022 and NCC 2025.
How much openable window does a room need for natural ventilation?
Openings that can be opened with a ventilating area of at least 5% of the room's floor area, open to a suitably sized court or space open to the sky, or to an open verandah, carport or the like (F6D7, the same in NCC 2022 and NCC 2025). In a Class 2 unit a room other than a sanitary compartment can borrow it through an adjoining room in the same unit: the opening between them at least 5% of the room's floor area, and the adjoining room's openings at least 5% of the two rooms' combined floor area (F6D8). Otherwise it needs mechanical ventilation to AS 1668.2 or, under NCC 2025, natural ventilation designed to AS 1668.4.
Does a bathroom without a window need an exhaust fan?
Unless it borrows ventilation through an adjoining room (a sanitary compartment cannot, F6D8) or, under NCC 2025, is naturally ventilated to AS 1668.4, it needs mechanical ventilation to AS 1668.2 (F6D6). In a Class 2 sole-occupancy unit the exhaust must draw at least 25 L/s and discharge to outdoor air, and if it does not run continuously it must be interlocked with the light switch with a 10-minute run-on (F8D4, the same in NCC 2022 and NCC 2025).
Which edition of AS 4254 applies to ductwork?
NCC 2022 with Amendment 2 and NCC 2025 both call up AS 4254.1:2021 for flexible duct and AS 4254.2:2012 for rigid duct, through Specification 7 (S7C5, fire hazard properties) and J6D7 (sealing the ducts of an air-conditioning system of 3,000 L/s or more). The Building Defects Library quotes the 2012 edition of AS 4254.1, whose clause numbers differ.
