Cutaway of a tropical wall showing cladding, a ventilated cavity, a wall wrap, insulation and lining, with humid air stopping at the wrap, on a warm-to-cool gradient background.

Condensation in climate zones 1 and 3: what NCC 2025 changes for warm-climate walls

In short

  • NCC 2025 brings climate zones 1 and 3 into the condensation management rules for the first time, through Housing Provisions Part 10.8 and Volume One Part F8.
  • In those zones, any control layer between the cladding and the outside of the insulation must meet a vapour permeance range that depends on whether the wall has a drained and ventilated cavity.
  • Zone 1 sets an upper limit: the wrap must be less than 1.1403 µg/N.s. The highly vapour-open wraps specified in cooler zones will not comply there.
  • Queensland moves to NCC 2025 on 1 May 2027 with no variation to these parts. NSW has varied them, so NCC 2022 condensation rules continue to apply in NSW.
  • Climate zone 2 is not covered by the vapour permeance table, and the roof ventilation rules still apply only in zones 6, 7 and 8.

Correct as at September 2026.

For years, condensation has been treated as a cold-climate problem. The ABCB’s own examples of cooler climates are Melbourne and Hobart. If you designed in the tropics, the wall membrane permeance rules simply did not reach you.

NCC 2025 changes that. Climate zones 1 and 3 now have wall membrane rules of their own, and they pull in the opposite direction to the southern rules many specifications were written for.

What changed

The ABCB lists the change plainly: NCC 2025 includes “climate zones 1 and 3 for the first time, to address condensation risk in warmer and mixed climates”. It also expanded vapour permeance requirements so they vary by climate zone and wall construction.

On the ABCB climate map, climate zone 1 is described as “high humidity summer, warm winter” and climate zone 3 as “hot dry summer, warm winter”. Check your site by address or postcode on the map, not by council boundary.

The rules sit in Part 10.8 of the ABCB Housing Provisions for Class 1 buildings, and in Part F8 of NCC Volume One for sole-occupancy units in Class 2 buildings and Class 4 parts of buildings.

The new vapour permeance limits

Clause 10.8.1(2) says any control layer between the cladding and the exterior side of the primary insulation layer must achieve the vapour permeance in Table 10.8.1. For zones 1 and 3:

Climate zoneWall constructionVapour permeance (µg/N.s)AS 4200.1 class (explanatory)
1No cavity≥ 0.0022 to < 1.14032 or 3
1Drained and ventilated cavity≥ 0 to < 1.14031, 2 or 3
3No cavity≥ 0.14293 or 4
3Drained and ventilated cavity≥ 0.00222, 3 or 4
The zone 1 trap. In zones 4 and 5, a wall without a cavity needs a Class 4 membrane, 1.1403 µg/N.s or more. In zone 1 the same wall needs less than 1.1403. A specification copied from a southern job can fail in the tropics without anyone changing a word.

Why the tropics run in reverse

The ABCB Condensation in buildings handbook explains the logic. In cooler climates, a higher permeance control layer lets internal moisture dry outwards. In tropical climates, lower permeance materials help limit moisture being driven inwards from outside. The handbook uses Cairns and Darwin as tropical examples.

Air conditioning is the driver. In zone 1, the handbook says the layer just behind the interior lining is often the coldest surface at risk when rooms are mechanically cooled, because cooled surfaces can fall below the dew point of the air. It also warns that low permeance vapour barriers on interior surfaces can increase condensation risk in air conditioned buildings, and that impermeable finishes such as vinyl wall coverings can add to it.

For raised timber floors, which are common in Queensland, the handbook flags a related risk: in air conditioned homes, moist subfloor air can migrate upward in summer. That is guidance, not a Deemed-to-Satisfy requirement, but it is worth reading before you detail a floor.

Cavities in zones 1 and 3

In zones 1 and 3, a drained and ventilated cavity is required where the wall has no pliable building membrane or water barrier between the cladding and the insulation (10.8.1(3)). Otherwise it is a design choice, unlike zones 6, 7 and 8 where it is mandatory. Either way, it changes the permeance you need. The cavity must:

  • sit between the cladding and the outside of the insulation or outermost control layer;
  • be at least 12 mm deep, built with battens, spacers or similar;
  • be unobstructed by any control layer and drained to the exterior; and
  • have openings of at least 1,000 mm² per metre of wall at the base and top, or at each storey where the cavity is closed.

Single skin masonry and concrete walls, full-height insulated sandwich panel walls, walls outside the building envelope and any part of a wall below natural ground level are exempt.

Which states and when

JurisdictionNCC 2025 condensation rules
QueenslandApply from 1 May 2027. NCC 2022 applies until 30 April 2027. No Queensland variation to Part 10.8 or F8 is listed.
New South WalesVaried. Part 10.8 of the NCC 2025 Housing Provisions and Part F8 of Volume One do not apply in NSW. The NCC 2022 Amendment 2 versions apply instead.
Western AustraliaBCA 2025 adopted 1 May 2026. BCA 2022 can be used until 30 April 2027.
South AustraliaBuilding Code of NCC 2025 applies from 1 May 2027.
TasmaniaHousing Provisions Part 10.8 is replaced with the 2022 version.
Northern TerritoryNCC 2025 not adopted.

So for NSW designers, even from 1 May 2027, the NCC 2022 condensation provisions stay.

What stays the same for warm climates

Climate zone 2 is not covered by the vapour permeance requirements. And the roof space ventilation provisions in 10.8.3 and 10.8.4, including the 18 mm roof space, apply only in zones 6, 7 and 8. The exhaust rules in 10.8.2 apply in every zone.

Your next steps

  1. Confirm the climate zone of every live Queensland project on the ABCB map.
  2. Check the permeance class on the data sheet of every wrap and sarking in your standard details.
  3. Decide cavity or no cavity early, because it changes the membrane you can use.
  4. Flag jobs that may be approved after 30 April 2027 so the right edition is applied.

CPD on condensation

A course on condensation in hot humid climates for zones 1 and 3 is in development. These live courses cover the NCC 2025 condensation rules now:

For the wider picture, read how to manage condensation in residential buildings, and see CPD in Queensland, the CPD requirements guide and the CPD deadlines calendar. Working in Queensland? Get the free Queensland guide.

Frequently asked questions

Do NCC 2025 condensation rules apply in climate zones 1 and 3?

Yes. NCC 2025 brings climate zones 1 and 3 into the condensation management provisions for the first time. Control layers outside the insulation in external walls must meet vapour permeance limits set by climate zone and wall construction.

What vapour permeance does a wall wrap need in climate zone 1?

Under Table 10.8.1 of the NCC 2025 Housing Provisions, a wall without a cavity needs 0.0022 to less than 1.1403 µg/N.s. With a drained and ventilated cavity, the range is 0 to less than 1.1403 µg/N.s.

When do the new condensation rules start in Queensland?

Queensland adopts NCC 2025 on 1 May 2027. NCC 2022 applies until 30 April 2027. No Queensland variation to the condensation provisions is listed.

Do the NCC 2025 condensation rules apply in NSW?

No. NSW has varied NCC 2025 so that Part 10.8 of the Housing Provisions and Part F8 of Volume One do not apply. The NCC 2022 Amendment 2 versions of those parts apply in NSW instead.

Is a wall cavity mandatory in climate zones 1 and 3?

Not in every case. In zones 1 and 3 a drained and ventilated cavity is required where the wall has no pliable building membrane or water barrier between the cladding and the insulation. Where a membrane is used, the cavity is a choice, but it changes the vapour permeance range the membrane must meet. Cavities are mandatory in zones 6, 7 and 8.

Sources