The short answer: NCC 2025 Volume Two changes are deliberately moderate. Building Ministers agreed to pause further residential energy efficiency changes until mid-2029 — the 7-star NatHERS minimum introduced in NCC 2022 remains in place. The primary residential changes are strengthened condensation management provisions (drained and ventilated cavities required as the DTS pathway in Climate Zone 7), restructured waterproofing requirements, and updated condensation-related roof ventilation. Several proposed changes — including EV charging readiness for homes — were removed from the final code.

NCC 2025 Volume Two addresses Class 1 buildings (houses, townhouses) and Class 10 non-habitable structures (garages, sheds, carports). The reforms are deliberately contained — Building Ministers agreed in October 2025 to pause residential energy efficiency changes until approximately mid-2029, except where essential safety or quality issues arise.

The focus in NCC 2025 for residential buildings is quality and durability — particularly addressing moisture, condensation and waterproofing defects that have become a significant source of building failure in Australian residential construction over the past decade.

Change 1: Condensation Management — Housing Provisions Part 10.8 and Volume One Part F8

This is the most significant residential change in NCC 2025 and the one with the greatest practical impact on external wall specification in Canberra.

Part 10.8 / F8  Strengthened Condensation Management — Drained Cavities Required Under DTS

What changed:  NCC 2025 introduces new control layer requirements for external walls. Any vapour barrier or water control layer installed on the exterior side of the primary insulation layer must meet vapour permeability requirements in all climate zones. Vapour permeability requirements for wall sarking are extended to all climate zones. For Canberra (Climate Zone 7, a high-condensation-risk zone): the DTS pathway now requires drained and ventilated cavities in external wall construction. Direct-fix cladding systems — those applied without a drained and ventilated cavity — do not comply under the DTS pathway unless the system can demonstrate hygrothermal performance through certified testing or documented evidence. This is not an absolute ban: a Performance Solution pathway remains available for systems that can demonstrate condensation management without a cavity. In practice, the majority of previously compliant direct-fix systems in Canberra will require a cavity retrofit or redesign for NCC 2025 compliance under the DTS pathway. Cavity dimensions are specified; ventilation calculation methods have changed. Roof ventilation requirements are also updated — for small roofs ventilation requirements are reduced; for steeper pitched roofs in cooler zones, airflow requirements increase. Note: condensation zoning uses heating degree day classifications that broadly align with but are not identical to the NatHERS climate zones.

Design impact:  The DTS pathway effectively makes drained and ventilated cavities standard for most Canberra residential projects. Brick veneer with its existing 40mm cavity remains compliant. For projects using fibre cement cladding, metal cladding, timber cladding or render systems in direct-fix applications, the specification must be reviewed against the cavity requirement. If a cavity system cannot be accommodated — for example, on tight urban sites where the additional 20–40mm of wall thickness across the perimeter affects setback compliance or floor area — a Performance Solution pathway is available but requires consultant documentation. On sites in RZ2 or other zones where setbacks are tight, the extra wall depth created by the cavity should be accounted for in early design to avoid setback exceedances that are discovered late.

ACT note:  All new Class 1 residential buildings in the ACT must comply with the condensation management provisions. The ACT variation exempting existing buildings from the new waterproofing provisions does not apply to condensation management in new residential construction.

Why Condensation Management Matters Specifically in Canberra

Canberra's Climate Zone 7 status — cold winters, wide diurnal swings and dry air — creates specific conditions for interstitial condensation risk within wall assemblies. Moisture that forms within the wall rather than on visible surfaces can accumulate over years, degrading insulation performance, causing timber decay and creating conditions for mould growth that is invisible until structural damage has already occurred.

The mandatory cavity in the DTS pathway creates a drained and ventilated path for moisture to escape rather than accumulate. For homeowners, this means new homes will be more durable and more resistant to the moisture-related defects that have become increasingly prevalent in Australian residential construction. For builders, it requires immediate review of external wall specifications for any new residential project in the ACT.

Change 2: Water Management — Restructured Provisions

Section F / Housing Provisions  Waterproofing — Falls Required in Structural Substrate Under DTS

What changed:  NCC 2025 restructures water management Performance Requirements with new defined terms and DTS provisions. For residential buildings: wet area and bathroom waterproofing under the DTS pathway requires membranes to be applied to the structural concrete substrate. Falls (typically 1:80 minimum) must be achieved in the structural concrete — not corrected by a screed or levelling compound between the substrate and the membrane. Where the structural slab cannot achieve compliant falls, a Performance Solution remains available — requiring consultant documentation and certifier agreement. Balcony waterproofing provisions are strengthened.

Design impact:  The substrate requirement changes the documentation obligation. Structural drawings must specify slab falls with the precision required to achieve compliant profiles in the poured concrete. A concreter working to a flat slab specification and then adding a screed for falls is not the DTS pathway under NCC 2025. Address falls in the structural documentation. Where concrete placement cannot reliably achieve compliant falls, engage a Performance Solution consultant before construction begins — not during. This is particularly relevant for bathrooms on upper floors where formwork and slab thickness constraints may make precise falls difficult to achieve.

ACT note:  New Class 1 residential buildings in the ACT are subject to the full waterproofing provisions. The ACT government variation exempting existing buildings from the new requirements does not apply to new builds.

Change 3: Structural Reliability and Performance Solutions

A2G2 / H1P1  Performance Solution Assessment Methods — Clarified

What changed:  Amendments to A2G2 (Performance Solution assessment) and H1P1 (Structural reliability and resistance — Housing Provisions) specify the assessment methods required to support consistent, robust Performance Solutions. These changes clarify the evidentiary requirements for any Performance Solution that varies from DTS provisions — including structural matters.

Design impact:  For standard residential construction, this change has minimal practical impact. For projects using non-standard structural systems, unusual site conditions or requiring Performance Solutions for any reason — including the waterproofing and condensation matters noted above — the documentation of the assessment methodology is more explicitly prescribed. Engage your certifier early on any Performance Solution to understand what evidence is required under NCC 2025.

ACT note:  ACT residential projects using Performance Solutions should confirm with the certifier what assessment documentation is required under the updated A2G2 and H1P1 provisions.

Change 4: EIFS — New DTS Pathway Under AS 5346:2023

Part H1  External Insulation and Finish Systems — New Referenced Standard

What changed:  NCC 2025 now references AS 5346:2023, providing a new DTS compliance pathway for External Insulation and Finish Systems (EIFS — typically render applied over polystyrene or mineral wool insulation board) under Part H1 (Structure). This simplifies structural compliance for these systems. However, EIFS systems must still satisfy the condensation management provisions — in Climate Zone 7, this means the EIFS system must either incorporate a compliant drained and ventilated cavity or demonstrate via certified testing that condensation management is achieved without one.

Design impact:  The new DTS pathway under AS 5346:2023 simplifies structural compliance for EIFS systems. But the condensation management interaction is important — a direct-fix EIFS system without a cavity does not comply under the DTS condensation pathway in Climate Zone 7. The structural compliance simplification does not remove the moisture management requirement.

ACT note:  For ACT projects specifying EIFS, confirm with the manufacturer and your building designer that the system includes a compliant cavity or has documented condensation performance evidence meeting NCC 2025 requirements for Climate Zone 7.

The Passive House Compatibility Question

A concern raised after the initial publication: does the mandatory cavity requirement conflict with Passive House airtightness? The answer is no — and understanding why is important for any high-performance residential project in Canberra.

In a correctly designed NCC 2025 compliant wall assembly, the control layers are sequenced as follows from inside to outside: interior lining → airtight membrane (whether interior or exterior to the frame) → frame with insulation → vapour-permeable sarking → drained and ventilated cavity → cladding. The cavity sits entirely outside the airtight layer. The airtight membrane remains continuous and undisturbed by the cavity.

For Passive House projects, the vapour-permeable sarking — which is required to be airtight in Passive House but vapour-open — satisfies both the NCC 2025 condensation management requirement (vapour permeability) and the Passive House airtightness requirement (air barrier continuity). The two requirements are complementary. They do require the design team to specify the control layer sequence correctly and ensure the sarking is detailed as a continuous air barrier with sealed laps and penetrations — but there is no inherent conflict between NCC 2025 condensation provisions and Passive House certification.

The 7-Star NatHERS Requirement

The 7-star NatHERS minimum for new Class 1 homes was introduced in NCC 2022 (the original edition published 2022). This requirement remains unchanged in NCC 2025 — Building Ministers specifically agreed to pause further residential energy efficiency changes until approximately mid-2029. The energy compliance standard you design and document to now is the standard that will apply for the next several years.

What This Means for Passive Solar Design in Canberra

The condensation management changes interact with passive solar design in an important way for Canberra homeowners pursuing high-performance homes. The cavity requirement under NCC 2025 must be integrated into the wall assembly alongside the insulation levels required for passive solar performance — and for Passive House certification.

The correct wall assembly for a high-performance Canberra home under NCC 2025 will typically be: structural frame with insulation in the cavity, vapour-permeable airtight sarking on the exterior of the frame, a drained and ventilated cavity of compliant dimensions, and then the external cladding. This assembly satisfies the condensation management requirements and supports passive solar performance simultaneously. The cavity adds 20–40mm of wall depth relative to a direct-fix assembly — a dimension that matters for setback compliance on tight urban sites and should be accounted for at schematic design.