NCC 2025 External Glazing: A Practical Guide to Window Energy Performance in Australian Homes

Windows and glazed doors are usually the part of a house where the most heat escapes in winter and where the most solar energy enters in summer. That is why the energy performance of external glazing is one of the most consequential parts of the residential energy rules in the National Construction Code 2025. If you are planning a new home, a major renovation, or a full window replacement, the question is no longer whether your windows must meet energy performance rules – it is which rules apply to your site, how performance is measured, and how you demonstrate that the windows pass.

This article is a practical guide to NCC 2025 external glazing windows Australia: it explains the residential glazing energy rules in plain English, and it is built on the official texts published by the Australian Building Codes Board (ABCB) – Part H6 (Energy efficiency) of NCC 2025 Volume Two, Part H6’s associated Specifications, and Part 13 (Energy efficiency), including Part 13.3 (External glazing), of the ABCB Housing Provisions. Throughout, code requirements are clearly separated from design advice, so you can tell which statements are obligations under the code and which are recommendations for a more comfortable, efficient home.

The guide also explains how a compliance-focused manufacturer, Meichen International Windows & Doors (MC Windows), documents the performance of its Australian window and door systems, so you know exactly which numbers to ask for when you are comparing products.

What Is the NCC 2025, and Who Must Comply?

The NCC in brief

The National Construction Code (NCC) is Australia’s model building code, developed and published by the Australian Building Codes Board. The NCC 2025 edition is published on the ABCB’s official NCC platform, and the volumes and the Housing Provisions are available as PDFs from the NCC 2025 edition page. Because the NCC is a model code, each state and territory adopts it in its own legislation with its own adoption date and its own set of variations. The edition that has legal effect for your project depends on where the building is and when work is approved or started. For example, in Queensland the NCC 2025 edition has legal effect from 1 May 2027.

For houses, the energy rules sit in two linked places: Part H6 (Energy efficiency) of NCC 2025 Volume Two, which applies to Class 1 and Class 10 buildings, and the ABCB Housing Provisions, which provide the practical deemed-to-satisfy (DTS) provisions for houses, including Part 13 (Energy efficiency) with its building fabric, external glazing, and sealing Parts.

DTS provisions and performance solutions

The NCC distinguishes between DTS provisions and performance solutions. DTS provisions are specific, measurable rules: if you follow them, your building is deemed to comply. A performance solution is an alternative route that demonstrates, by other means such as engineering assessment or advanced simulation, that the performance requirements are still met. Part H6 is organised around performance requirements – H6P1 for thermal performance and H6P2 for energy usage of domestic services – with the verification methods in H6 (H6V2 and H6V3) and the Housing Provisions providing the step-by-step DTS path that most residential projects use.

When the window energy rules apply

The Part H6 verification methods apply to a Class 1 building and to an enclosed Class 10a building attached to a Class 1 building – for example an attached garage. They are not intended for detached garages or open carports. The Housing Provisions Part 13.3 (External glazing) applies to Class 1 buildings and to Class 10a buildings that contain a conditioned space. In practice, that means the window energy rules apply to houses, townhouses, and the attached carport or workshop of a house.

Two cautions. First, state variations matter: in New South Wales the adopted NCC 2025 deletes H6V2, and in Western Australia the application clause for Part 13.3 has been replaced by a state-specific version. Always confirm which adopted version applies in your jurisdiction. Second, energy efficiency compliance is normally assessed at building permit approval (or, where no permit is required, at commencement of construction), so check which edition your certifier must apply before you finalise window schedules.

Key Definitions: U-Value, SHGC, Climate Zones, and the Language of Part 13.3

Total system U-value

The U-value of a window measures how fast heat flows through it, expressed in watts per square metre per kelvin (W/m2K). A lower U-value means better insulation and less heat loss in winter. What matters for the NCC calculations is the Total System U-Value: the performance of the complete window – frame, glass, spacer and all – not the glass alone. Assessor bodies that rate whole windows often publish this figure under slightly different names, including “U Factor” or “Uw”. When you are comparing windows, always ask for the total system figure, because a low-U glass pane in a standard single-glazed aluminium frame performs very differently from the same glass in a thermally broken system.

Solar Heat Gain Coefficient (SHGC)

The Solar Heat Gain Coefficient is the fraction of incident solar radiation that passes through a window and is ultimately available as heat inside the space, expressed as a number between 0 and 1. A low SHGC admits less solar heat – useful where summer cooling dominates. A higher SHGC admits more low winter sun – useful where heating dominates. In the NCC 2025 winter glazing calculation, the SHGC value used in the formula is capped at 0.7. As with U-value, the relevant figure for the code check is the Total System SHGC of the complete window assembly.

Climate zones 1 to 8

The NCC divides Australia into eight climate zones, defined in the NCC glossary with a national climate zone map (Figure 2). Zone 1 covers the hot northern regions, and the zones progress south and inland through hot, warm, temperate, and cool conditions, with Zone 8 covering the cold southern alpine and highland regions. Your zone determines which glazing checks apply to your project: the winter glazing check applies in climate zones 2 to 8, and the summer glazing check applies in climate zones 1 to 7. A single site is always in one zone, and your building certifier can confirm it from your address.

Code requirements versus design advice

Read this section as the map for the rest of the article. Where a clause number is cited – H6P1, H6P2, H6V1, H6V2, H6V3, Specification 44, or Housing Provisions clauses 13.2, 13.3, and 13.4 – the statement is a code requirement as published in the NCC 2025, and it applies in its binding form only once the NCC 2025 has legal effect in your state or territory, subject to that jurisdiction’s variations. Where this article says “design advice” – strategies for orientation, shading, glazing choice beyond the minimum, and product selection – it is professional guidance for a better-performing house, not an obligation. If you are ever unsure which side of that line a statement sits on, your building certifier is the right person to ask.

NCC 2025 external glazing windows Australia: What the Code Actually Requires

This section translates the official NCC 2025 text into plain language. Every clause reference below is to the NCC 2025 edition as published by the ABCB, and the clause texts are the source of the requirement – this guide is an explanation, not a substitute for the code.

Winter glazing limits (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 of the building – including any mezzanine – must not exceed the allowances obtained from Table 13.3.2a of the Housing Provisions. In simple terms, each storey gets a budget of allowed heat flow, and the glazing in that storey must stay inside the budget.

The calculation weights every window by its area and by a set of factors defined in the clause: the Total System U-Value of each glazing element; its Total System SHGC (not exceeding 0.7 for this formula); a winter exposure factor (EW) that reflects orientation and floor type; a bedroom conductance factor (BC); an orientation sector conductance factor (OC); and further factors for rooflights, shading, and window configuration (RW, LW, and related factors in the formula). The practical message: winter performance rewards low total system U-values everywhere, and it rewards or penalises solar gain depending on where the window faces. South-facing and west-facing glazing loses the most heat in the cold zones, while north-facing glazing receives the low winter sun.

Summer glazing limits (clause 13.3.3, climate zones 1 to 7)

In climate zones 1 to 7, the aggregate solar heat gain of the glazing in each storey, again including any mezzanine, must not exceed the allowance obtained by multiplying the floor area of that storey – measured within the enclosing walls – by a constant CSHGC from Table 13.3.3a. The clause formula sums, over every glazing element, the product of area, Total System SHGC, and a set of factors including a summer exposure factor (ES) that varies with orientation sector, floor construction, and – in zone 5 – wall construction (lightweight or masonry veneer versus concrete or masonry).

External shading has an explicit place in the calculation. An external shading device that complies with clause 13.3.4(b) is considered to achieve a P/H value of 2.00, and where the clear gap under a shading device exceeds 500 mm, the projection (P) must be halved. In cooling-dominant climates, well-designed eaves, pergolas, and shades can be a genuine compliance tool – not just an aesthetic feature.

Orientation sectors and true north

The exposure and conductance factors in both the winter and summer calculations depend on the orientation sector of each window. The NCC defines eight orientation sectors, measured clockwise from true north on the plan (Figure 13.3.2a). The figure notes are explicit that magnetic north, as read from a compass, is not an acceptable approximation – you must use the true north bearing from the survey, because magnetic declination varies by location and over time. A two-degrees-of-error issue on a large north wall can change which sector a window falls in, and therefore which factors apply.

The whole-building thermal check (H6P1 and Specification 44)

Passing the per-storey glazing ratios is necessary but not sufficient. Performance requirement H6P1 requires that the total heating load, the total cooling load, and the total thermal energy load of the habitable rooms and conditioned spaces in the building do not exceed the limits set out in Specification 44 (Specifications 44.1, 44.2 and 44.3). Those limits are whole-building numbers: your windows, walls, roof, slab, ventilation, and shading all feed into them. A window schedule that passes Part 13.3 in isolation can still drag a whole house past the Specification 44 limit – which is why residential energy compliance is assessed at the level of the whole building, not the individual window.

The reference building method (H6V2)

One of the DTS verification routes in Part H6 compares the proposed building against a “reference building” – a virtual baseline house of the same size and form with a defined fabric. Under H6V2, compliance with the thermal performance requirement is verified when, compared to that reference building using the same calculation method and location-specific data, the proposed building has: in climate zone 1, a cooling load equal to or less than the reference; in climate zone 8, a heating load equal to or less than the reference; and in climate zones 2 to 7, both heating and cooling loads equal to or less than the reference.

The reference building itself is not a straw man: the code requires it to comply with the DTS provisions of Parts 13.2 (Building fabric), 13.3 (External glazing) and 13.5 (Ceiling fans) of the Housing Provisions. The comparison must use identical assumptions for both buildings – climate data for the location, adjoining structures, soil conditions, orientation, floor plan, number of storeys, roof construction, glazing layout, and operating schedules. The calculation method must comply with ANSI/ASHRAE Standard 140 and be capable of modelling the fabric, glazing and shading, infiltration and ventilation, and the sensible part of the heating and cooling load. The clause also fixes the assumptions: heating thermostats at 20 degrees C; cooling thermostats at 24 degrees C for bedrooms and 27 degrees C (zones 1-4) or 26 degrees C (zones 5-8) elsewhere; defined occupancy and internal gains; and an air infiltration rate of 0.75 air changes per hour, or a blower-door-derived rate where additional sealing is provided. Remember the state variations: NSW’s adopted NCC 2025 deletes H6V2, so NSW projects must use the provisions applicable in that jurisdiction.

Energy usage and building sealing (H6P2, Part 13.4, H6V3)

The energy rules are not only about the fabric. H6P2 requires that the energy value of the building’s domestic services – heating, cooling, domestic hot water, and lighting – does not exceed 70% of a defined reference case (based on 3-star ducted heat pumps, a 5-star instantaneous gas water heater, and a lighting power density of 4 W/m2). Building sealing is part of the same performance picture: the DTS path verifies sealing through Part 13.4 of the Housing Provisions or through H6V3 (verification of building envelope sealing). A window that is thermally efficient on paper but installed with poor seals and gaps performs as a leaky wall in winter and summer alike – sealing is where window energy performance is won or lost in practice.

Two Ways to Demonstrate Compliance

The deemed-to-satisfy route

Most residential projects demonstrate energy compliance the straightforward way: apply the Housing Provisions to the fabric and glazing, run the checks in Part 13.2, 13.3 and 13.4, verify the whole building against H6P1 and Specification 44 (including the reference building comparison where H6V2 applies in your jurisdiction), verify domestic services against H6P2, and keep the paperwork. Done correctly, the outcome is deemed compliance – no further judgement calls required.

AFRC-rated windows and performance documentation

The explanatory notes to Part 13.3 recognise that assessors using AFRC procedures may publish their performance values under slightly different terms – “U Factor” or “Uw” for Total System U-Value, and “SHGC” for Total System SHGC. The note confirms that such values can be used in the Part 13.3 calculations provided they measure the combined glass and frame performance according to AFRC requirements. The practical translation: ask your window supplier for total system (whole window) U-value and SHGC from an accredited assessor, and make sure the figures cover the exact system and glazing configuration you are specifying. Glass-only numbers will not do.

The performance solution route

Where the DTS route does not suit – unusual site geometry, heritage constraints, large glazed envelopes, or designs that intentionally trade one element against another – the NCC allows a performance solution under Part A2. A performance solution demonstrates that the performance requirements (H6P1 and H6P2) are met by other means, typically with engineering-level thermal modelling. This route is more flexible and more expensive, and it should be agreed with your certifier before design is locked. Note that in Western Australia, for existing buildings undergoing alterations, extensions, or associated pool work, the adopted NCC references the older NCC 2019 provisions as an option instead of NCC 2025 Part H6 – another reason to confirm the local rules early.

Compliance Checklist for Homeowners, Designers and Builders

Work through this list before window orders are placed. Items 1-11 are code-related checks (where the NCC 2025 has legal effect in your jurisdiction); the final item is good-practice documentation.

• Confirm the adopted edition and date. Check which NCC edition your state or territory has adopted, its legal effect date, and its variations – for example, Queensland’s NCC 2025 takes effect 1 May 2027; NSW has deleted H6V2; WA has replaced the 13.3.1 application clause.
• Identify the climate zone. Use the NCC climate zone map (glossary, Figure 2) for your address. Winter checks apply in zones 2-8; summer checks in zones 1-7.
• Collect total system values. For every window and glazed door, obtain documented Total System U-value and Total System SHGC from an accredited assessor (AFRC-rated values are acceptable where they measure combined glass and frame performance).
• Run the winter check (13.3.2). For zones 2-8, the conductance and solar heat gain ratio for each storey must not exceed the Table 13.3.2a allowance, using the clause formula and factors.
• Run the summer check (13.3.3). For zones 1-7, the aggregate solar heat gain per storey must not exceed floor area multiplied by the Table 13.3.3a constant, using the clause formula and factors.
• Apply true north orientation. Assign each window to its orientation sector using the survey’s true north bearing – not a compass reading.
• Apply shading correctly. Use the P/H factors for any external shading; a device compliant with 13.3.4(b) counts as P/H 2.00, and P is halved where the gap exceeds 500 mm.
• Complete the whole-building check (H6P1). Verify the total heating, cooling, and thermal energy loads against the Specification 44 limits.
• Verify the reference building comparison (H6V2) where applicable. Confirm the load comparison for your zone and that the reference building complies with DTS Parts 13.2, 13.3 and 13.5.
• Check sealing and fabric. Confirm the building sealing provisions (Part 13.4 or H6V3), fabric insulation (13.2.2), thermal break requirements (13.2.3(7), 13.2.5(5)), and floor edge insulation (13.2.6).
• Verify domestic services (H6P2). Confirm the energy value of heating, cooling, hot water and lighting is within the 70% reference limit.
• Document everything. Keep the assessor data, calculations, shading drawings and survey orientation for the building certifier and for future resale energy disclosure. Install windows to the applicable installation standard – Meichen’s Australian product lines are certified to AS4666 (installation) – and keep installation records with the file.

Design Advice: Choosing Windows Beyond the Minimum

Everything in this section is design advice. It is not a code requirement, and nothing here changes what the NCC 2025 demands – it only explains how to get a more comfortable, lower-running-cost house once the minimum is met.

Strategy by climate zone

In cooling-dominant climates (roughly zones 1 to 3, and the warmer parts of zone 4), the sensible strategy is low-SHGC glazing on the north, east and west, generous external shading, and careful control of west-facing glass, which receives harsh late-afternoon sun. In heating-dominant climates (zones 6 to 8), the strategy reverses: low total system U-values everywhere, higher-SHGC glazing to the north to harvest low winter sun, and minimal unshaded west glazing. In the mixed, temperate zones in between, balance – lower SHGC on the problem orientations, better SHGC where the winter sun is wanted, and strong insulation in the frame. In all zones, the whole-building check means the glazing decision should be made together with the roof, walls, slab and ventilation design, not in isolation.

Thermally broken aluminium frames and Low-E glazing

Standard aluminium is an excellent conductor of heat, so a thermally broken frame – with an insulating barrier separating the outer and inner sections – is the standard tool for bringing a large aluminium window’s total system U-value down to useful levels. Low-emissivity (Low-E) coatings on the glass let visible light through while reflecting heat, and double or triple glazing with gas fills adds the air-layer insulation that single glazing cannot match. Meichen International Windows & Doors (MC Windows) is a specialist in exactly this combination: its thermal break product lines – including the MC100 series (awning, fixed, tilt & turn and double hung) and the MC140 sliding door – use thermal break construction with double and triple Low-E glazing, and its Australian product lines are certified to the Australian standards that matter for residential fenestration: AS2047 (windows and doors), AS4284 (performance of windows), AS1288 (glass in buildings), AS4666 (installation) and AS2208 (safety glazing), across 43 certified product series. Meichen also demonstrates water tightness up to 960 Pa under AS4284 – a useful margin against driving rain in a coastal climate – and it has been dedicated to the Australian and New Zealand market since 2017, backed by 18-19 years of industry experience and a 20,000 square metre manufacturing facility. Meichen is actively pursuing CodeMark certification, the highest level of certification in Australia.

Match the product to the opening

Ultra-slim frames – a signature of Meichen’s design language – maximise glass area and minimise frame obstruction, which is why they suit luxury villas, townhouses and apartments that want unobstructed views. Design advice: the more glass you specify, the more the glazing values drive the whole-building numbers, so use the total system figures for the exact slim-frame configuration you are buying, and pair large glazed areas with the shading and orientation strategies above. For a coastal site, water tightness and air tightness ratings matter as much as the U-value – ask for the tested ratings in writing.

Frequently Asked Questions

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

No. The residential DTS pathway does not set a single star rating for windows. It sets measurable checks: the total system U-value and SHGC ratio tests in Part 13.3 (winter in zones 2-8, summer in zones 1-7), the whole-building load limits in H6P1 and Specification 44, and the supporting fabric, sealing and services requirements. Window star-rating schemes exist in the Australian market, but NCC 2025 compliance for houses is demonstrated through the clause checks described in this article.

What is the difference between U-value and SHGC?

U-value measures conductive heat loss – how fast heat leaks through the window in winter; lower is better. SHGC measures solar heat gain – how much of the sun’s energy the window lets in; in cooling climates lower is generally better, while in heating climates a higher SHGC on the north side can be a benefit. A well-designed window in a given climate gets both numbers right, and the NCC checks do exactly that through the separate winter and summer calculations.

When do I need the reference building check?

The reference building comparison (H6V2) is one of the DTS routes for verifying the whole-building thermal performance requirement (H6P1). It is needed when your project demonstrates compliance that way in a jurisdiction where H6V2 applies – note that NSW’s adopted NCC 2025 deletes the clause. The proposed building must beat or match the reference building’s heating load (zones 2-7 and 8), cooling load (zones 2-7 and 1), or both, using the same calculation method and data.

Can single glazing ever comply under the NCC 2025?

It can, in limited cases: in some northern, cooling-dominant zones, the winter conductance test may be achievable with single glazing because the winter requirement is comparatively relaxed. But the whole-building load limits in H6P1 and Specification 44 make single glazing a difficult choice for most of Australia, particularly in the mixed and cold zones. Treat single glazing as a case-by-case question for your certifier or energy modeller – not a default.

How do I find out which climate zone my address is in?

The NCC glossary defines climate zones with Figure 2, the national climate zone map, and the ABCB’s NCC website lets you browse provisions by zone. In practice, your building certifier will confirm the zone for your site as part of the energy assessment – it is a quick, definitive step, so do not rely on memory or on the nearest city.

How does Meichen support NCC 2025 compliance?

Meichen International Windows & Doors (MC Windows) documents the performance of its Australian lines against the standards the code ecosystem relies on: 43 product series certified to AS2047, AS4284, AS1288, AS4666 and AS2208, thermal break systems with double and triple Low-E glazing, and tested water tightness up to 960 Pa under AS4284. Whether a specific Meichen configuration meets the total system requirements for a specific site is a project-level question – the right step is to request the total system U-value and SHGC for the exact series and glazing you are specifying, and let the energy assessment confirm. MC Windows is based at mcwindow.com.au, with local partnerships in Sydney and its manufacturing facility in Zhaoqing, Guangdong, China.

Conclusion

In short, NCC 2025 external glazing windows Australia compliance comes down to a handful of well-defined checks: the winter conductance and solar heat gain ratio in clause 13.3.2 for climate zones 2-8, the summer solar heat gain limit in clause 13.3.3 for zones 1-7, the whole-building heating, cooling and thermal energy load limits in H6P1 and Specification 44, the reference building comparison where H6V2 applies, and the supporting sealing and domestic services requirements. Get the total system U-value and SHGC for the exact products you are buying, orient every window from true north, and keep the documentation your certifier will ask for.

Just as important is the distinction this guide has drawn throughout: the cited clauses are code requirements where the NCC 2025 has legal effect in your jurisdiction, while the selection strategies – shading, orientation and climate-zone playbooks, slim-frame trade-offs – are design advice that goes beyond the minimum. A house that merely passes is different from a house that performs. For Australian window and door systems with documented total system performance, thermal break construction, Low-E double and triple glazing, and 43 certified product series, Meichen International Windows & Doors (MC Windows) at mcwindow.com.au is a compliance-focused manufacturer to ask for the numbers.

References

1. Australian Building Codes Board, National Construction Code 2025 (NCC 2025 edition portal, including Volume Two and the Housing Provisions), accessed 27 September 2026: https://ncc.abcb.gov.au/editions/ncc-2025
2. Australian Building Codes Board, NCC 2025 hub (state and territory adoption dates, supporting information and overview of key changes), accessed 27 September 2026: https://ncc.abcb.gov.au/ncc-2025
3. Australian Building Codes Board, NCC 2025 Volume Two, Part H6 Energy efficiency (H6O1, H6P1, H6P2, H6V1, H6V2, H6V3, including state variations), accessed 27 September 2026: https://ncc.abcb.gov.au/editions/ncc-2025/adopted/volume-two/h-class-1-and-10-buildings/part-h6-energy-efficiency
4. Australian Building Codes Board, NCC 2025 Volume Two, Specification 44 (Calculation of heating load limit, cooling load limit and thermal energy load limit), accessed 27 September 2026: https://ncc.abcb.gov.au/editions/ncc-2025/adopted/volume-two/h-class-1-and-10-buildings/44-calculation-heating-load-limit-cooling-load-limit-and-thermal-energy-load-limit
5. Australian Building Codes Board, Housing Provisions, Part 13.3 External glazing (clauses 13.3.1-13.3.4, Tables 13.3.2a-13.3.3x, Figures 13.3.2a-13.3.2b, explanatory notes including AFRC rating values), accessed 27 September 2026: https://ncc.abcb.gov.au/editions/ncc-2025/adopted/housing-provisions/13-energy-efficiency/part-133-external-glazing
6. Australian Building Codes Board, Housing Provisions, Part 13.4 Building sealing, accessed 27 September 2026: https://ncc.abcb.gov.au/editions/ncc-2025/adopted/housing-provisions/13-energy-efficiency/part-134-building-sealing
7. Meichen International Windows & Doors (MC Windows), product and certification information: https://mcwindow.com.au

Clause references (H6O1, H6P1, H6P2, H6V1-H6V3, Specification 44, and Housing Provisions Parts 13.2-13.5) in this article are cited from the NCC 2025 texts published by the ABCB and are current as published on the ABCB NCC platform at the date of access. This article is general information only and is not building, legal or energy advice; confirm the adopted edition, variations and calculations for your specific project with a qualified building certifier.

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