NCC 2025 and windows: stricter solar admittance criteria for commercial glazing, and an allowance for shading by vertical projections

The short answer, by who you are

• Building or renovating a house (Class 1). The national window and glazing clauses in the ABCB Housing Provisions read the same in NCC 2025 as in NCC 2022, on our side-by-side reading of Parts 8.2, 8.3, 8.4 and 13.3. Western Australia is the exception to check: its schedule now varies two of those Parts (below).
• Glazier, facade or shading supplier on commercial work. The Deemed-to-Satisfy limits for glazed walls of Class 3 and Class 5 to 9 buildings are lower in NCC 2025, and the shading calculation now counts vertical projections. The allowance for an external shutter, blind or screen is unchanged.
• Anyone selling an internal blind or curtain on energy grounds. The commercial shading clause, in both editions, names external devices only.

What the ABCB says changed

The Australian Building Codes Board's release notice says NCC 2025 came out on 1 May 2026 and that The most significant technical changes in NCC 2025 apply to new commercial buildings. Its page on the commercial energy changes lists, among other things, stricter solar admittance criteria for wall-glazing constructions, and says These changes apply to Class 3 and Class 5 to 9 buildings such as hotels, offices, retail, hospitals, and schools.

Two lines in the ABCB's list of amendments for Volume One carry the window changes. Against clause J4D6: Total system U-Values, solar admittance values and R-values for walls and glazing have been updated. Against S37C7, the shading clause: Amended to allow for shading of glazing by vertical projections.

Solar admittance is defined in the NCC 2025 glossary as The fraction of incident irradiance on a wall-glazing construction that adds heat to a building's space. A lower maximum is a stricter limit.

The commercial numbers, side by side

We read clause J4D6 in both editions. For the group that covers offices and shops (Class 5, 6, 7, 8 and 9b buildings, and Class 9a buildings other than ward areas), NCC 2022 set one solar admittance limit per climate zone for every aspect. NCC 2025 sets a separate limit for each aspect, lower in every case we tabled.

The hotel and care group (Class 3 and 9c buildings, and Class 9a ward areas) moves the same way: NCC 2022 set solar admittance limits between 0.07 and 0.10 depending on zone and aspect; NCC 2025 sets 0.06 for every zone and aspect. Its U-value limits moved both ways: lower in climate zones 2 and 5 (2.0 to 1.6), the same in zone 1, and higher in five zones, for example 1.1 to 1.6 in zone 6.

One wording change reaches every pane, not only shopfronts. NCC 2022 said The Total System U-Value of display glazing must not be greater than U5.8. NCC 2025 says The Total System U-Value of glazing, including display glazing, must not be greater than U5.8.

Apartments are outside all of this. The Volume One list says A new Note is introduced referring to Section J of NCC 2022 Amendment 2 for Class 2 buildings. Their energy rules stay with NCC 2022.

Shading: what is new, and what is not

Specification 37 is where a designer works out how much shade a window gets, as a multiplier on its solar admittance. In NCC 2022, clause S37C7 offered two routes: a permanent horizontal projection over the window, read from two tables; or a flat multiplier for an external shading device. NCC 2025 adds a third: an external permanent projection that extends vertically for the height of the glazing, with three new tables for northern, western and eastern aspects, and a multiplier of 1.0, meaning no reduction, for the southern aspect. The multiplier for each window is now the lesser of the routes that apply.

The device route is word for word the same in both editions. The multiplier is 0.35 for shading that is provided by an external shading device such as a shutter, blind, vertical or horizontal building screen with blades, battens or slats, which is capable of restricting at least 80% of summer solar radiation and, if adjustable, will operate automatically in response to the level of solar radiation. Neither edition's clause mentions internal blinds or curtains.

For houses: what we compared, and the one change nearby

We read the national clauses of the ABCB Housing Provisions Parts 8.2 (windows and external glazed doors), 8.3 (glass), 8.4 (glazing human impact) and 13.3 (external glazing, the energy rules for house windows) in the NCC 2025 edition and in the NCC 2022 edition the ABCB still publishes online, with every table shown, and compared them line by line. Two lines differ. Clause 8.2.2 now spells load bearing as two words, and Part 8.4 now points to H1D8(3)(a) where it pointed to H1D8(3). Every figure in the Part 13.3 tables is the same.

That matches the ABCB's own list of amendments for the Housing Provisions, which names no change in Section 8 or Part 13.3. Its only energy-efficiency entries are 13.2.5, Amended to allow for overhangs greater than those specified in NCC 2022., and 13.2.6, Amended to clarify application for waffle pod slabs. The 13.2.5 change is to the wall insulation tables, not the windows: where NCC 2022's widest overhang band was capped (for example over 1,800 mm and up to 2,400 mm), NCC 2025 leaves it open (over 1,800 mm). The ABCB adds that it has attempted to include all major changes and gives no warranty on the list, which is why we compared the clauses ourselves.

A house can also comply through a separate Volume Two pathway that uses house energy rating software. The Volume Two list of amendments shows two entries under Part H6, energy efficiency, both clarifications in Specification 42: one removes a reference to the definition of floor area, the other is Amended to clarify (d) applies for slab edge insulation.

Western Australia is different. Its NCC 2025 schedule varies Parts 8.2, 13.2 and 13.3. The WA glazing variation says references to climate zone 6 in Figure 2 and Table 3 under the definition of climate zone in the Schedule 1 may be considered as climate zone 5 for Part 13.3. The WA window installation variation adds an exemption: 8.2.2(b) does not apply to windows in a masonry wall element. That is the 10 mm gap above the window. The WA schedule in the NCC 2022 online edition, read the same day, lists no variation to Parts 8.2 or 13.3.

When it applies where you build

The ABCB says States and territories can adopt NCC 2025 from 1 May 2026, subject to jurisdictional implementation arrangements. Its adoption table, read 7 October 2026, shows this.

Our read

This section is opinion, built on the clauses above.

For a homeowner, the useful news is a non-event: if your builder or window supplier says the new code forces different windows on a house, ask which clause. Outside WA, the national house glazing clauses did not move.

For the shading trade, the commercial changes cut two ways. Lower solar admittance limits make every shading multiplier worth more to a designer trying to comply on the Deemed-to-Satisfy route, and that includes the unchanged 0.35 for an external blind, shutter or screen. But the new vertical-projection tables give designers a fixed, no-moving-parts alternative on east and west walls. The two conditions on the device route also matter in a quote: a product only earns 0.35 if it can restrict at least 80% of summer solar radiation and, if adjustable, operates automatically. A manually operated external blind does not meet the second condition as written. That is our reading of the clause, not a ruling; the building surveyor on the job decides.

And the clause still names only external devices. Whatever an internal blind does for comfort, it is not in this calculation.

Sources

1. Australian Building Codes Board, NCC 2025 released, 1 May 2026 (read 7 October 2026): the release date, that states and territories can adopt from 1 May 2026, and that the most significant technical changes apply to new commercial buildings.
2. Australian Building Codes Board, NCC 2025 state and territory adoption information (read 7 October 2026): every adoption date and transition period in our table, and the variations warning.
3. Australian Building Codes Board, NCC 2025, commercial energy efficiency changes (read 7 October 2026): the stricter solar admittance criteria for wall-glazing constructions, and that the changes apply to Class 3 and Class 5 to 9 buildings.
4. Australian Building Codes Board, List of amendments, NCC 2025 Volume One (read in a browser 7 October 2026): the J4D6 and S37C7 entries and the Class 2 note.
5. NCC 2025 Volume One, Part J4 Building fabric (read in a browser with tables shown, 7 October 2026): clause J4D6 and Tables J4D6a to J4D6d.
6. NCC 2022 Volume One, Part J4 Building fabric (read in a browser with tables shown, 7 October 2026): clause J4D6, its U-value limits and Tables J4D6a to J4D6c.
7. NCC 2025 Volume One, Specification 37, Calculation of U-Value and solar admittance (read in a browser 7 October 2026): clause S37C7 and Tables S37C7a to S37C7e.
8. NCC 2022 Volume One, Specification 37, Calculation of U-Value and solar admittance (read in a browser 7 October 2026): clause S37C7 as it stood.
9. NCC 2025 Volume One, Schedule 1 glossary (read in a browser 7 October 2026): the definitions of solar admittance, wall-glazing construction and display glazing.
10. Australian Building Codes Board, List of amendments, ABCB Housing Provisions (NCC 2025, read in a browser 7 October 2026): the Section 13 entries, the absence of any Section 8 or Part 13.3 entry, and the no-warranty statement.
11. ABCB Housing Provisions, NCC 2025: Part 8.2, Part 8.3, Part 8.4, Part 13.3 and Part 13.2 (each read in a browser with all clauses and tables open, 7 October 2026).
12. ABCB Housing Provisions, NCC 2022: Part 8.2, Part 8.3, Part 8.4, Part 13.3 and Part 13.2 (each read the same way, 7 October 2026), and the edition's Western Australia schedule.
13. ABCB Housing Provisions, NCC 2025, Schedule 11 Western Australia: WA Part 13.3 and WA Part 8.2 (read in a browser 7 October 2026).
14. Australian Building Codes Board, List of amendments, NCC 2025 Volume Two (read in a browser 7 October 2026): the two Part H6 entries.

How we did this. NCC Online is a JavaScript application, so every clause page was opened in a full browser with all clauses expanded and tables shown, and its text saved. We compared each NCC 2025 page with the matching NCC 2022 page line by line, ignoring the 2019 cross-reference labels the 2022 edition carries and the way equations render. The comparison covers the national clauses and tables of the Parts named above; state variations were read only for Western Australia. NCC 2022 was amended after its first release; we compared against the NCC 2022 text the ABCB publishes online today. Commercial limits are the Deemed-to-Satisfy limits; a building can also comply through a Performance Solution or a verification method, which we have not compared. We have not contacted the ABCB.

Work in glazing or shading and read a clause differently? Tell us and we will check it at the source and log the outcome here.