NCC 2025 condensation management: what changed and when it applies

The ABCB says condensation has been identified as a significant contributor to building defects, particularly in cooler and mixed climates and in more airtight buildings. Knowing which edition of Part 10.8 a home was built to, and what it asked for, helps you explain a finding to an owner, builder or property manager.

Where the condensation rules sit

For houses (Class 1 buildings), NCC 2025 Volume Two sets the Performance Requirement in H4P7: "Risks associated with water vapour and condensation must be managed to minimise their impact on the health of occupants." The Deemed-to-Satisfy route in H4D9 is to follow Part 10.8 of the ABCB Housing Provisions. For a Performance Solution, the Verification Method in H4V5 models a roof or external wall and shows that a mould index greater than 3, as defined in AIRAH DA07, does not occur on the inside face of the water control layer or on the building fabric inside it.

Volume One Part F8 covers apartments and other buildings, and the ABCB says it was strengthened in the same way. This page deals with the Housing Provisions.

NCC 2022 and NCC 2025 side by side

Walls: vapour permeance by climate zone

A pliable building membrane or sarking-type material used as a control layer in an external wall must comply with AS 4200.1 and be installed to AS 4200.2. Any control layer between the cladding and the outside of the primary insulation must meet the vapour permeance in Table 10.8.1, measured in µg/N.s.

The explanatory notes map these ranges to the vapour permeance classes in AS 4200.1: class 4 in climate zones 6 to 8 with a cavity, class 3 or 4 in zones 4 and 5 with a cavity and class 4 without one. The ABCB explains the logic: in cooler climates a more permeable layer lets internal moisture dry outwards, while in tropical climates a less permeable layer limits outdoor moisture being driven in.

A drained and ventilated cavity sits between the cladding and the insulation or outermost control layer. It must be at least 12 mm deep, unobstructed by any control layer, drained to the outside, and have openings with a free area of at least 1,000 mm² per metre of wall at the base and top of the cavity, or at each storey where the cavity is closed. Single skin masonry or concrete walls, full insulated sandwich panel walls, walls outside the building envelope and any part of a wall below natural ground level are exempt.

Roofs in climate zones 6, 7 and 8

Insulation not parallel to the roof plane (10.8.3), for example insulation laid on a flat ceiling under a pitched roof: there must be a roof space at least 18 mm high immediately above the insulation, ventilated to outdoor air. For a pitch of 10° to under 75°, that means 7,000 mm²/m at the eaves or low level and 5,000 mm²/m at high level or the ridge. Under 10°, it is 20,000 mm²/m at the eaves or low level, or at each of two opposing ends for gable roofs; skillion roofs need 20,000 mm²/m low and 5,000 mm²/m high (7,000 and 5,000 for skillion roofs under 10 m²).

Insulation parallel to the roof plane (10.8.4): the roof space sits immediately above the insulation, or above a control layer laid on it, must not be blocked by insulation, must be at least 18 mm high measured square to the roof, and needs 20,000 mm²/m low and 5,000 mm²/m high (7,000 and 5,000 for roofs under 10 m²). A control layer laid directly on the insulation must have a vapour permeance of at least 1.14 µg/N.s.

Vent areas are per metre of the roof's longest plan dimension: the low level total uses twice that length (once for mono pitch and skillion roofs), and the high level total uses it once. High level openings are at the ridge or no more than 900 mm, or a third of the roof height, below the highest point, whichever is less. Concrete roofs, insulated sandwich panel roofs, roofs subject to BAL-FZ under AS 3959 and tiled roofs without a control layer above the insulation are exempt.

Exhaust fans: unchanged, but worth checking

Clause 10.8.2 is the same in both editions. Exhaust systems need at least 25 L/s for a bathroom or sanitary compartment and 40 L/s for a kitchen or laundry, and must discharge directly or through a shaft or duct to outdoor air; so must a venting clothes dryer. A fan that does not run continuously, serving a bathroom or toilet that is not naturally ventilated, must be interlocked with the light switch and have a 10 minute run-on timer. Rooms without natural ventilation need make-up air, for example an opening of 14,000 mm² to the next room, which the ABCB says a 20 mm undercut on a 700 mm door provides.

When NCC 2025 applies, state by state

The NCC takes effect through each state and territory's building laws, so adoption dates differ.

Two variations matter most for condensation. The NSW variation says "Part 10.8 of the ABCB Housing Provisions 2025 does not apply in NSW and Part 10.8 of ABCB Housing Provisions 2022 Amendment 2 applies in NSW." In Tasmania, Part 10.8 is replaced with Part 10.8 of the ABCB Housing Provisions 2022, and the Tasmanian variation to H4D9 points designers to the "Condensation in Buildings Tasmanian Designers' Guide". In the NCC 2025 text on NCC Online, only NSW and Tasmania vary Part 10.8. So the new wall and roof rules are in use in the ACT, Victoria and WA (where the transitions let NCC 2022 still be used until 2027) and apply in Queensland and SA from 1 May 2027. For Victoria, also check the Victorian Building Authority's NCC 2025 amended variations.

Transition periods mean a home finished in 2027 or later may still have been designed to NCC 2022. In WA, for example, most applicants can use the code in effect when the building permit application is made or the one in effect 12 months earlier. Check with the state building regulator rather than going by the completion date.

What to record on a mould inspection

An inspection does not certify a building against the NCC, but it can record the evidence a builder, building surveyor or owner needs. Useful things to note:

• Context: the state, the climate zone for the address, and the approval date if the owner has it, so the right edition and variation can be identified.
• Walls: whether there is a wall wrap and any product or class marking you can see, whether there is a cavity behind the cladding, and whether its vents at the base and top are open or blocked.
• Roof space: whether insulation is on the ceiling or under the roof, the gap between insulation and sarking or roofing, eaves and ridge vents and anything blocking them, and mould or staining on sarking, battens or rafters.
• Exhaust fans: each fan's location and whether it works, where it discharges (outdoors, or into the roof space), whether there is a run-on timer, whether a door undercut or other make-up air path exists, and how a vented dryer is ducted.
• Moisture evidence: readings, temperature and relative humidity, dew point, and dated photos of mould, condensation and staining, room by room.

Where DampApp Pro fits

• Offline on site: record rooms, walls, roof space defects and moisture readings with photos, with no reception needed.
• Dew point on the device: enter temperature and relative humidity and the app calculates dew point, so you can show why a surface was condensing.
• Fan schedule: record each exhaust fan's location, type and whether it worked when tested. The app does not measure flow rates; if you measure one with your own instrument, add it to the notes.
• Dated photos: the report can show each photo's capture time from its EXIF data, or the time it was added.
• A PDF before you leave: the report is built on your device, with optional AI help to turn shorthand into clear wording you check.

The hygrothermal moisture risk calculator can help you screen a wall for condensation risk, but it is not the H4V5 Verification Method and does not show NCC compliance.

Free to start: surveys work offline and free PDFs carry a small app footer. Pro adds your own branding, cloud sync and the full toolkit.

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