NCC 2025 External Glazing: How Australian Homeowners Should Specify Windows

Buying windows for a new Australian house used to hinge on style, hardware and price. Under the National Construction Code 2025 (NCC 2025), it hinges on a fourth thing: documentation. The residential energy rules treat external glazing as a main driver of a house’s heating and cooling load, checked per storey, with the total system U-value and total system SHGC of every window feeding calculations your building certifier runs before the permit is signed. A specification without those numbers in writing is an invitation to delay.

The phrase that captures the subject is NCC 2025 external glazing Australian windows: the measurable checks that apply to the glass and frames in your house, and the paperwork that proves your exact configuration passes them. This guide walks a homeowner through that process – the edition, climate zone and orientation that apply, the two performance numbers that matter, a window schedule a certifier can assess, and how to separate a genuine data pack from a brochure.

Cited clause numbers reflect the NCC 2025 texts published by the Australian Building Codes Board (ABCB); “design advice” goes beyond the code minimum. Meichen International Windows & Doors (MC Windows) appears as an example of documented manufacturer performance, so you know what to ask for when comparing suppliers.

Why NCC 2025 Makes Window Specification a Written Job

The energy rules that reach your windows

For houses (Class 1 buildings) and outbuildings (Class 10), the energy provisions sit in Part H6 of NCC 2025 Volume Two. Performance requirement H6P1 limits the total heating load, total cooling load and total thermal energy load of the habitable rooms and conditioned spaces to the limits in Specification 44 (Specifications 44.1, 44.2 and 44.3). Those are whole-building numbers: windows, roof, walls, slab, ventilation and shading all feed into them, so a schedule that looks fine on its own can still drag the house past a limit. H6P2 adds that the energy value of domestic services must not exceed 70 per cent of a defined reference case, and the DTS routes H6V1 to H6V3 cover thermal performance, the reference-building comparison and envelope sealing.

Edition, adoption date and state variations

The NCC is a model code: each state and territory adopts its own edition with its own legal effect date and variations. Queensland’s adopted NCC 2025 takes legal effect from 1 May 2027, and New South Wales’s adoption deletes the H6V2 reference-building route. The first line of any window specification should therefore be the adopted edition, its legal effect date and the state variations – confirmed by your certifier in writing, not assumed.

The Two Numbers That Drive the Specification

Total system U-value

The U-value measures how fast heat flows through the window, in watts per square metre per kelvin (W/m2K); lower is better. The figure the code calculations use is the Total System U-value: frame, glass, spacer and all, not the glass alone – sometimes published by assessors as “U Factor” or “Uw”. Because the frame is part of the number, the same low-U glass performs very differently in a standard aluminium frame than in a thermally broken one, which is why your schedule must pin down the frame system, not just the glazing.

Total system SHGC, and the 0.7 cap

The Solar Heat Gain Coefficient (SHGC) is the fraction of incident solar radiation that ultimately enters as heat, from 0 to 1. A low SHGC helps where summer cooling dominates; a higher SHGC admits more low winter sun, which helps where heating dominates. In the NCC 2025 winter glazing formula the SHGC used is capped at 0.7. As with U-value, the relevant figure is the Total System SHGC of the complete assembly you are buying.

Why “a typical configuration” is not buildable

A slim sliding window with triple Low-E glazing will not carry the same total system figures as an awning window with double glazing, even within one product family. If a quote lists numbers for “a typical configuration” only, treat that as a red flag: the schedule must state the series, size family, operation and glazing package per opening, with matching assessor data attached. AFRC-rated values are acceptable where they measure the combined glass-and-frame performance.

How the NCC 2025 external glazing Australian Windows Checks Apply to Your House

Winter check, clause 13.3.2 (climate zones 2 to 8)

In climate zones 2 to 8, the ratio of the conductance (Cu) and solar heat gain (CSHGC) of the glazing in each storey – including any mezzanine – must not exceed the allowances in Table 13.3.2a of the Housing Provisions. Each storey effectively gets a heat-flow budget, and every window in it is weighted by area and by defined factors: total system U-value, total system SHGC (capped at 0.7), a winter exposure factor (EW), a bedroom conductance factor (BC), an orientation sector factor (OC), and further factors for rooflights, shading and window configuration. The lesson: low total system U-values pay off everywhere, and solar gain is rewarded or penalised depending on which wall the window sits on.

Summer check, clause 13.3.3 (climate zones 1 to 7)

In climate zones 1 to 7, the aggregate solar heat gain of each storey’s glazing – again including mezzanines – must not exceed the storey floor area within the enclosing walls, multiplied by a CSHGC constant from Table 13.3.3a. The formula sums, over every element, area times total system SHGC times a summer exposure factor (ES) that varies with orientation sector, floor construction and, in zone 5, wall construction. In cooling-dominant climates the west wall is the most expensive wall in the house: low-SHGC glazing or external shading there is a compliance decision, not a preference.

Orientation: true north, not compass north

The NCC defines eight orientation sectors measured clockwise from true north (Figure 13.3.2a), and the notes are explicit that a compass reading is not an acceptable approximation: magnetic declination varies by location and over time, so a couple of degrees of error on a large north wall can move a window into a different sector and change the factors that apply. Record the survey’s true north bearing in the specification file.

Shading changes the math

External shading has a formal place in the calculation: a device complying with clause 13.3.4(b) is taken to achieve a P/H value of 2.00, and where the clear gap under it exceeds 500 mm the projection (P) must be halved. Eaves and shades can be a genuine compliance tool in cooling-dominant zones, but their dimensions must be agreed before the window schedule is locked, because the shading changes the numbers the windows must meet.

Building Your Window Schedule, Step by Step

Step 1: Fix the edition, zone and orientation

Confirm with the certifier which adopted edition and variations apply; identify the NCC climate zone for the address from the glossary Figure 2 map (zone 1 covers the hot north, zone 8 the cold southern highlands); and record the survey true north bearing. Write all three into the specification header.

Step 2: List every opening

For each window and glazed door: size, floor (including mezzanines), orientation sector, frame series, operation – fixed, awning, sliding, tilt and turn, double hung – and glazing configuration: single, double or triple, Low-E, gas fill. Nothing left as “typical”.

Step 3: Request configuration-specific performance data

Ask the supplier for the Total System U-value and Total System SHGC of the exact series, size family, operation and glazing package, from an accredited assessor. That is the pack the certifier’s energy assessment will actually test.

Step 4: Specify safety glazing and installation

State that glass in hazardous locations complies with AS2208 and that installation follows AS4666, with installation records kept in the compliance file. A window performs to its rated figures only when it is installed to the applicable standard.

Step 5: Lock the schedule before the permit

Energy compliance is normally assessed at building permit approval (or at commencement of construction where no permit is required), and changes to the schedule after approval trigger a new assessment. The schedule, the performance data and the shading dimensions should all be final before the permit package goes to the certifier.

A Short Compliance Checklist for Homeowners

Run any window specification or supplier quote against this list before signing:

Adopted NCC edition, legal effect date and state variations confirmed in writing.
Climate zone for the address identified (glossary Figure 2).
Survey true north bearing recorded; orientation sector assigned per opening.
Per-storey schedule complete, with mezzanines included.
Total System U-value and Total System SHGC attached for each exact configuration.
Winter (clause 13.3.2, zones 2-8) and summer (clause 13.3.3, zones 1-7) ratios checked by the assessor.
Whole-building Specification 44 limits (H6P1) addressed in the energy calculation.
External shading dimensions agreed before the schedule is locked.
AS2208 safety glazing stated for hazardous locations; AS4666 installation specified with records retained.
Documentation pack – assessor data, configuration drawings, calculation inputs – agreed as part of the contract.

What a Credible Supplier’s Documentation Looks Like

The standards that matter for residential fenestration

The Australian standards a residential window specification should name are AS2047 (windows and doors), AS4284 (performance of windows), AS1288 (glass in buildings), AS4666 (installation) and AS2208 (safety glazing). A manufacturer whose product lines are certified against these can evidence the claims your schedule makes; one that cannot should answer why, in writing.

Meichen as an example of documented performance

Meichen International Windows & Doors (MC Windows) is a useful benchmark for what “documented” looks like: 43 Australian product series certified to AS2047, AS4284, AS1288, AS4666 and AS2208; thermal break systems with double and triple Low-E glazing across the MC100 series (awning, fixed, tilt and turn, double hung), the MC140 sliding door and the MA73 bi-fold door; ultra-slim systems such as the SD205-AS960 coastal sliding and stacker doors and the SLMA100-20 slim sliding window; and tested water tightness up to 960 Pa under AS4284 – a useful margin for coastal sites. Meichen has served the Australian and New Zealand market since 2017, backed by 18-19 years of industry experience and a 20,000 square metre facility in Zhaoqing, Guangdong, with local partnerships in Sydney, and is actively pursuing CodeMark certification. None of this replaces the total system numbers for your exact configuration: request them, and let the energy assessment confirm.

Frequently Asked Questions

Does the NCC 2025 set a single star rating for windows?

No. The residential DTS path sets measurable checks instead: the per-storey winter and summer glazing ratios in Part 13.3, the whole-building limits in H6P1 and Specification 44, and the reference-building comparison where H6V2 applies in your state. Rating schemes exist in the market, but code compliance for houses is demonstrated through the clause checks, not a star label.

Do single-glazed windows ever pass?

Treat single glazing as a case-by-case question for your certifier or energy modeller rather than a default. The per-storey ratios may be achievable in some mild zones, but once the whole-building Specification 44 limits are considered, single glazing is difficult for most of Australia. If a supplier cannot give you total system numbers for the single-glazed configuration, you do not have enough information to specify it.

Why does the frame matter so much?

Because the code calculations use total system values. Aluminium conducts heat readily, so a frame without a thermal break can dominate the U-value of even a good glass package. A thermally broken frame – an insulating barrier between the outer and inner sections – is the standard way to bring that number down, and it is why the schedule must name the frame system for every opening.

When must the window schedule be final?

Before building permit approval in most projects, because energy compliance is assessed at permit approval or, where no permit is required, at commencement of construction. Lock the schedule, the performance data and the shading dimensions before the permit package goes to the certifier.

Conclusion

Specifying windows under the NCC 2025 is a documentation discipline before it is a product choice. The edition and state variations tell you which rules apply; the climate zone and true north orientation sectors tell you how each wall is weighted; the per-storey checks in clauses 13.3.2 and 13.3.3 tell you what your glazing ratios must achieve; and the whole-building limits in H6P1 and Specification 44 tell you the windows must be designed with the rest of the house. When NCC 2025 external glazing Australian windows comes up in your project – at the architect’s office, the certifier’s counter or the supplier’s showroom – the answer is the same every time: pin the exact frame-and-glass configuration in writing, get the total system numbers for it, run the per-storey and whole-building checks before ordering, and keep the documentation your certifier will ask for.

References

Australian Building Codes Board, National Construction Code 2025 (NCC 2025 edition portal, including Volume Two and the Housing Provisions), accessed 30 September 2026: https://ncc.abcb.gov.au/editions/ncc-2025
Australian Building Codes Board, NCC 2025 hub (state and territory adoption dates and key changes), accessed 30 September 2026: https://ncc.abcb.gov.au/ncc-2025
Australian Building Codes Board, NCC 2025 Volume Two, Part H6 Energy efficiency (H6P1, H6P2, H6V1-H6V3, including state variations), accessed 30 September 2026: https://ncc.abcb.gov.au/editions/ncc-2025/adopted/volume-two/h-class-1-and-10-buildings/part-h6-energy-efficiency
Australian Building Codes Board, Housing Provisions, Part 13.3 External glazing (clauses 13.3.1-13.3.4, Tables 13.3.2a and 13.3.3a, Figure 13.3.2a), accessed 30 September 2026: https://ncc.abcb.gov.au/editions/ncc-2025/adopted/housing-provisions/13-energy-efficiency/part-133-external-glazing
Meichen International Windows & Doors (MC Windows), product and certification information: https://mcwindow.com.au