NCC 2025 Class 2 Glazing and Energy Efficiency: A Practical Apartment Guide

If you own, manage, or live in an apartment, the way your windows and building envelope perform can influence day-to-day comfort, running costs, daylight, and how straightforward it is to keep the building compliant. This NCC 2025 Class 2 glazing energy efficiency apartment guide breaks down what the National Construction Code (NCC) expects of multi-unit residential buildings, how the energy performance of glazing is assessed, and what you should verify before design, construction, or a retrofit. It is written in plain English and prioritises practical, actionable steps over dense code language, so you can use it as a working reference.

Understanding NCC 2025 and Class 2 Buildings

The National Construction Code is the technical code that sets the minimum standards for building work across Australia. It is developed and published by the Australian Building Codes Board, commonly known as the ABCB. The NCC is organised into Volumes; Volume One deals with the design and construction of buildings, which is the part most relevant to apartments. The 2025 edition continues the code’s regular cycle of review and update, so provisions around thermal comfort, glazing, and energy use should be checked against the edition that is in force for the building work in question.

Before you look at any specific requirement, it helps to understand how the NCC categorises buildings. Classifications determine which provisions apply, so misidentifying the class of a building can lead to the wrong assumptions about compliance.

What “Class 2” Means in the NCC

Class 2 covers multi-unit residential buildings. In practical terms this is the category that most apartment and unit complexes fall into: buildings with more than one storey, or buildings containing two or more dwellings, that are not classified as a different residential class. A single family home is Class 1, while a large apartment building or a complex of units is Class 2. Because Class 2 buildings house multiple owners and residents in a shared structure, the code places particular weight on the collective performance of the building fabric, including the windows, walls, roof, and external envelope.

The distinction matters because Class 2 buildings are assessed as a whole rather than dwelling by dwelling in many respects. Design decisions made for the external envelope, the orientation of the building, and the glazing in the shared and individual units all interact. This is why a glazing or energy question in an apartment rarely has an answer that belongs to a single resident — it is usually a building-level decision.

The Role of the ABCB and the 2025 Edition

The ABCB is the national standards body responsible for developing and maintaining the NCC. Its website is the authoritative source for the code itself, explanatory documents, and information about how and when amendments take effect. When a provision is described in this guide, the ABCB’s published NCC is the document you should consult to confirm the exact wording and the edition that applies to your work. Local and state building regulators may also operate the code with additional local provisions, so the code and the local regulatory layer should both be considered.

For anyone working with a 2025-era project, the key practical point is that “which edition applies” is a decision made by the building work and its approval timing. If you are retrofitting, extending, or re-glazing, the relevant edition and its application date will shape the requirements. Confirming this early saves costly surprises later.

NCC 2025 Class 2 glazing energy efficiency apartment guide: what to check first

This section is the heart of the guide: the practical sequence of checks you should run before committing to a glazing or energy decision in a Class 2 apartment building.

Start with the edition and application date that governs your work. Then move to the classification to confirm Class 2 applies to the building or part of it. Next, identify the performance requirements for glazing and the energy efficiency provisions that apply to the building as a whole. Only then should you evaluate specific window products or retrofit options. Finally, confirm the compliance pathway — whether a prescriptive approach, a performance-based approach, or a combination of both is appropriate.

Running this sequence keeps the work grounded in the code rather than in assumptions. It also makes it far easier to explain your reasoning to a building surveyor, an engineer, a strata or body corporate committee, or a resident who is asking why a particular change is or is not acceptable.

The Glazing Performance Requirement

The NCC contains dedicated provisions on the energy performance of glazing in buildings. In Volume One, the glazing requirement is found within Part H1P2, which sets out performance requirements for the energy performance of windows in new building work. The intent of these requirements is to ensure that glazing contributes to, rather than undermines, the overall thermal and energy performance of the building. In a Class 2 apartment, the external windows, balconies, and any large glazed areas are a significant part of the envelope, so their performance carries real weight in the overall outcome.

The requirement is expressed as a performance objective rather than a list of mandated product specifications. That means there is not a single “approved window” that every building must use. Instead, the glazing must achieve an acceptable level of energy performance, and the way it is demonstrated depends on the compliance pathway chosen.

Prescriptive and Performance Pathways

The NCC generally offers more than one route to demonstrate compliance. A prescriptive pathway uses specific rules and methods: if you follow the referenced standard and its procedure, you are taken to meet the requirement. A performance pathway is more flexible: you define the outcome you must achieve and then demonstrate it using accepted evidence, which may include a recognised assessment method or a peer-reviewed technical argument.

For glazing, the prescriptive route is commonly supported by a recognised standard that provides a method for assessing the energy performance of windows, and that is discussed in the next subsection. Choosing between pathways is a design decision. A prescriptive approach can be simpler and more predictable, while a performance approach can offer more freedom when an unusual design, orientation, or product is being used. In practice, many Class 2 projects use a blend, applying a standard method for the bulk of the windows and a performance argument where there is a distinctive architectural or thermal feature.

How Glazing Energy Performance Is Assessed

The widely referenced standard for assessing the energy performance of glazing in buildings in Australia and New Zealand is AS/NZS 4200. It provides a method for determining whether the glazing in a building meets the energy performance expectations, taking into account how windows interact with the building and their context. Rather than judging a window in isolation, the assessment considers the role of the glazing within the overall building envelope.

For AS 2047, which covers the design of glazing in buildings, this is the companion standard that addresses the structural and safety aspects of putting glass in a building. Energy performance and safe, structurally sound glazing are related but separate matters, and a complete glazing decision for a Class 2 apartment should consider both.

Two practical implications follow. First, “will this window keep the apartment comfortable” is an energy-performance question that belongs to the assessment method, while “is this window safe and structurally adequate” is a design standard question. Second, in a multi-unit building the two are often decided by different people and at different stages, so it helps to name which of the two you are answering whenever you raise a glazing issue. Mixing them up is a common source of confusion in strata and body corporate discussions.

Energy Efficiency in Class 2 Apartments

Glazing is only one part of a building’s energy story. The NCC also contains broader provisions on the energy efficiency of buildings as a whole, which in Volume One are addressed under Part H1P5. These provisions consider how the building fabric, the thermal performance of the envelope, and the building’s systems work together so that the building does not consume energy needlessly. For an apartment building, this means the walls, roof, floor, glazing, and any shared systems are evaluated in combination.

The reason the code takes a whole-building view is that the energy performance of one element depends on the others. A very high-performance window can be wasted if the walls around it are poor, and an efficient roof can be undermined by a wall of glazing that lets in excessive heat. In a Class 2 building, where units share walls, floors, and sometimes services, the collective effect is what the energy efficiency provision is ultimately concerned with.

The Building Energy Efficiency Provisions

Part H1P5 sets out the performance requirements that a building’s overall energy efficiency must meet. It is a design-stage provision: it is satisfied during the design and documentation of the building, and it is the point at which the interaction between envelope and systems is most influenceable. Once a building is constructed, the energy efficiency framework is much harder to alter, which is one reason getting it right early is so valuable.

For apartments specifically, this means that the shared decisions — the orientation of the building, the proportion of glazing, the insulation approach, and the configuration of any shared heating, cooling, or hot-water systems — are where the energy efficiency outcome is largely set. Individual residents have relatively little ability to change these after the fact, which makes the design-stage decisions consequential for everyone who lives there.

Balancing Light, Ventilation, and Thermal Comfort

A good glazing and energy strategy does not chase a single number. It balances several things at once: adequate daylight and views, healthy natural ventilation, thermal comfort across the seasons, and reasonable energy use. These goals can pull in different directions. A large window brings light and a view but also greater heat gain and loss. A highly insulated, low-transmission window improves energy performance but can reduce passive solar gain if that was part of the heating strategy.

In a Class 2 apartment, the balance is set by the building’s orientation, its exposure, and the mix of north, east, west, and south-facing glazing. Because residents occupy units at different times and with different habits, the design has to work for a range of use patterns rather than a single ideal occupant. This is one reason the code’s performance approach, which allows the assessment to reflect the actual building and its context, is well suited to multi-unit residential work.

Practical Apartment Checklist

Use this checklist to work through a glazing or energy question for a Class 2 apartment building. You do not need to answer every item in one sitting; the point is to confirm the sequence and to catch gaps before money is spent.

Confirm the NCC edition and the application date that govern the proposed building work.
Verify that the building, or the part being worked on, is correctly classified as Class 2.
Identify the glazing performance requirement (Part H1P2) that applies to the windows, balconies, and external glazed areas.
Identify the building energy efficiency requirement (Part H1P5) and how the envelope is assessed as a whole.
Choose the compliance pathway: prescriptive via a recognised standard, performance-based, or a blend of both.
Confirm that the energy performance of the glazing is assessed using an accepted method such as AS/NZS 4200.
Confirm that the structural and safety design of the glazing follows AS 2047.
Check that the glazing strategy balances daylight, ventilation, views, and thermal comfort rather than optimising one at the expense of the others.
Review how shared walls, floors, and services in the apartment building affect the overall energy efficiency outcome.
Identify who is responsible for each decision: developer, designer, building surveyor, strata or body corporate, or individual owner.
Document the reasoning and the evidence used to demonstrate compliance, in a form a surveyor or engineer can review.
Where retrofit is proposed, confirm which provisions apply to the altered work and whether the original building’s compliance is affected.
Seek advice from a qualified professional — a building surveyor, an energy or thermal engineer, or a glazing specialist — before finalising any glazing or energy decision.

Practical Considerations for Owners, Managers, and Residents

How you act on this guidance depends on your role in the building. The same code requirements are experienced very differently by a developer, a body corporate, and an individual resident.

For Developers and Designers

Designers have the greatest influence, because the energy efficiency and glazing decisions are made before construction. This is where the whole-building view should be applied: orientation, envelope, glazing proportion, and shared systems should be considered together. Using a recognised assessment method for the glazing and a clear compliance pathway for the energy efficiency requirement makes the design easier to document and easier for a building surveyor to accept. Getting the interaction between envelope and systems right at this stage is far less expensive than trying to correct it after the building stands.

For Body Corporate and Strata Managers

For an established apartment building, the manager’s task is usually about change control. When a re-glazing, a balcony enclosure, a window replacement, or a common-area energy measure is proposed, the manager should confirm the compliance pathway and make sure the decision is made at the building level where it belongs. Because Class 2 buildings are assessed collectively, a change that affects the external envelope or the energy performance should generally be treated as a building-level decision rather than a single-owner decision. Keeping a record of the reasoning and the evidence supports both good governance and any later audit of compliance.

For Individual Residents

Individual residents have the least ability to change the building’s core energy performance, but they still have useful actions. Understanding why a particular window or balcony decision was made helps residents participate sensibly in body corporate or strata discussions. Where a resident is considering a change that affects the external envelope, the right first step is to check with the body corporate or strata committee and, if needed, with a building surveyor, before spending money. Knowing the difference between an energy-performance question and a structural-safety question, as described earlier, makes these conversations more productive and less likely to go in circles.

Frequently Asked Questions

Does the NCC 2025 apply to my existing apartment?: The NCC generally applies to building work when it is carried out. An existing, unmodified building is not usually “rebuilt” to the current edition. However, when work such as re-glazing, extending, or altering the external envelope is proposed, the provisions that apply to that work need to be confirmed against the relevant edition and its application date. This is a decision to make with a building surveyor rather than an assumption to make alone.
Is there a single approved window that Class 2 apartments must use?: No. The NCC sets a performance requirement for the energy performance of glazing rather than a list of mandated products. Compliance is demonstrated through a chosen pathway — prescriptive via a recognised standard, or performance-based with accepted evidence. That means different buildings, and even different parts of a building, can legitimately use different glazing.
What is the difference between the glazing requirement and the energy efficiency requirement?: The glazing requirement (Part H1P2) addresses the energy performance of windows specifically. The energy efficiency requirement (Part H1P5) addresses the building’s overall energy performance, considering the envelope and systems together. A window can meet the glazing requirement while still needing to be considered as part of the whole-building energy efficiency outcome. The two work together rather than replacing each other.
Which standard is used to assess the energy performance of windows?: AS/NZS 4200 is the widely referenced standard that provides a method for assessing the energy performance of glazing in buildings in Australia and New Zealand. It is the standard typically associated with the prescriptive compliance route for glazing. AS 2047 is the companion standard that addresses the structural and safety design of glazing.
Who decides glazing and energy matters in an apartment building?: Decisions that affect the external envelope or the building’s overall energy performance are generally building-level decisions. In a Class 2 building these are typically handled by the developer and designer at the design stage, and by the body corporate or strata committee for changes to an existing building. Individual residents contribute through consultation but usually do not make these decisions unilaterally.
Can a resident replace their own windows?: Usually not without checking. Because windows form part of the external envelope of a Class 2 building, a resident’s replacement window can affect compliance and the building’s collective energy performance. The resident should consult the body corporate or strata committee and, where appropriate, a building surveyor before proceeding, and should confirm the applicable compliance pathway.
Why does orientation matter for glazing in an apartment?: Because the thermal behaviour of glazing depends on the direction it faces. Windows facing different directions gain and lose heat differently across the seasons, so a glazing strategy that works on one side of the building may not be the right choice on another. A performance-based assessment allows the strategy to reflect the actual orientation and context of the building rather than applying a one-size-fits-all rule.
What is the single most important first step?: Confirm the NCC edition and application date that govern your specific building work, and confirm that Class 2 applies. Everything downstream — the glazing requirement, the energy efficiency requirement, and the compliance pathway — depends on getting these two facts right first.

Official NCC and ABCB References

The following are the authoritative sources to consult for the exact wording, the applicable edition, and official guidance. This guide summarises and explains; the primary documents below remain the controlling references.

Australian Building Codes Board (ABCB) — the national body that develops and publishes the National Construction Code. Official site: abcb.gov.au.
National Construction Code (NCC), Volume One: Building Design and Construction — the primary code for building design and construction, including the provisions for Class 2 buildings.
NCC Volume One, Part H1P2 — Glazing: performance requirements for the energy performance of windows in buildings.
NCC Volume One, Part H1P5 — Energy efficiency: performance requirements for the overall energy efficiency of buildings.
AS/NZS 4200 — Energy performance of glazing in buildings: the method for assessing the energy performance of windows, commonly used in the prescriptive compliance route.
AS 2047 — Glazing in buildings: the standard covering the design of glazing and other transparent materials in buildings, including structural and safety considerations.

Where any detail in this guide appears to differ from the published NCC, the NCC prevails. Always confirm the edition in force and any applicable state or local provisions before acting on building work.

Conclusion

Managing glazing and energy efficiency in a Class 2 apartment building is fundamentally about sequencing: establish the governing edition and application date, confirm the Class 2 classification, identify the glazing performance requirement and the whole-building energy efficiency requirement, and then choose a defensible compliance pathway. The code is built around performance rather than a single mandated product, which gives designers real flexibility but also places the responsibility for making the right choices on the people involved.

Throughout this NCC 2025 Class 2 glazing energy efficiency apartment guide, the consistent theme is that apartments are collective projects. The decisions that shape comfort and energy use are made at the building level, they are best made at the design stage, and they should be balanced across daylight, ventilation, views, and thermal comfort rather than optimised for one goal alone. By working through the checklist, understanding the difference between the glazing and energy efficiency provisions, and relying on the official NCC and ABCB references, owners, managers, designers, and residents can approach glazing and energy questions with confidence and with a defensible, code-grounded reasoning process.