Replacing Windows in a Strata Apartment: Approvals, By-Laws and Class 2 Compliance in Australia

Replacing the windows in a strata apartment is not a renovation decision — it is a building-control decision wrapped in a governance process. The glass and frames are usually common property, the wall they sit in is usually load-bearing or fire-rated, the building is usually Class 2 under the National Construction Code (NCC), and the work happens above, beside and below other people’s homes. Anyone who treats it as “just new windows” will lose three to six months to a rejected application, or worse, be ordered to remove installed product at their own cost.

The short answer: in most Australian strata schemes you need (1) owners corporation approval through the correct instrument — often a special resolution or a by-law — and (2) a technical package that proves the replacement product meets AS 2047, AS 1288, the NCC Class 2 provisions, and any acoustic or energy conditions already attached to the building approval. Both parts are required. Neither substitutes for the other.

This guide sets out the actual sequence, the documents that get approvals across the line, and the technical traps that catch owners, builders and installers on apartment window replacement projects.

Key takeaways

• External windows and the wall they sit in are commonly common property in strata schemes, so the owners corporation — not the lot owner — usually controls replacement.
• Approval is normally by special resolution or by-law, governed by state or territory strata legislation, not by a national rule.
• Every replacement must be shown to comply with AS 2047 (performance), AS 1288 (glass selection), the NCC Class 2 fire, energy and access provisions, and any acoustic conditions in the original development consent.
• Match the existing tested system wherever possible. Changing frame depth, glazing mass or opening type can invalidate the building’s performance evidence.
• Installation in occupied buildings needs an access, make-safe and waste plan approved with the application, not after.
• Realistic timelines run 8 to 20 weeks from first enquiry to installation; product lead time is usually the smaller part of that.

1. First question: who actually owns the window?

Almost every dispute about apartment window replacement starts here. In a strata scheme, the boundary between lot and common property is defined by the strata plan. In practice, for most Class 2 residential buildings:

• The external wall and the structure within it are common property.
• The window frame and glazing set into that wall are typically common property, even though only one lot enjoys them.
• Internal linings, reveals, blinds, curtains and floor coverings are usually lot property.

There are exceptions. Some schemes, particularly older or specially drafted plans, define windows as lot property, and some states treat certain elements differently. Read the strata plan and the registered by-laws before assuming anything, and get the strata manager’s written position on the ownership of the specific opening.

Why it matters: if the window is common property, the lot owner cannot unilaterally replace it, and the owners corporation has a positive duty to maintain and repair it. That duty is the lever a lot owner can use when a window has failed — a perished seal, a fogged insulated glass unit (IGU), a seized winder, or a frame that leaks in driving rain. If maintenance is being deferred, the owner can request the owners corporation act, and in most jurisdictions can escalate to a tribunal if it refuses.

2. The approval pathway by jurisdiction

Strata law is state-based. The instrument you need depends on where the building sits and how the scheme’s by-laws are drafted. The table below summarises the common position; always confirm against the current Act and the scheme’s own by-laws.

Two practical notes on this table. First, quorum and voting thresholds are where applications die: a 75% special resolution in a 60-lot scheme requires real campaigning, and postal or electronic voting rules differ by state. Second, a by-law granting exclusive use usually transfers maintenance responsibility to the lot owner — which may be exactly what the owner wants, but they should understand they are accepting a permanent obligation, not just winning a vote.

A well-prepared applicant does three things before lodging: circulates a one-page plain-English summary of the work, provides the technical evidence pack (Section 3), and offers conditions the owners corporation will want — insurance, qualified installer, defect liability period, restoration of common property, and a maintenance obligation.

3. The technical evidence pack

Approvals move quickly when the pack answers every question a committee, a strata manager and a certifier will ask. A complete pack for a window replacement typically contains:

The most common gap is the structural verification. Apartments are tall, exposed and often in terrain categories that generate much higher design wind pressures than a detached house. A window certified for a 6 kN/m² ultimate limit state test on a suburban home may be entirely unsuitable at level 12 on an exposed coastal site. The product certificate must be read alongside the site’s calculated pressure, not instead of it.

The second most common gap is energy compliance. In most states, replacing glazing is assessed as an alteration. If the new glazing has a higher U-value or a materially different SHGC than what was approved, the building may no longer satisfy its NCC energy performance pathway. That is a genuine approval risk, and it is why energy evidence belongs in the first lodgement, not in the eighth week.

4. NCC Class 2: the technical rules that actually bind

Class 2 buildings — residential apartments — carry obligations that Class 1 houses do not. Four matter most for windows.

Performance and weatherproofing. AS 2047 is the gateway standard. It establishes structural sufficiency, water penetration resistance and air infiltration performance, and it is the reference used by certifiers and insurers. For high-rise work, look for tested water resistance to the W4 level with test pressures in the order of 960 Pa for exposed coastal projects, and wind pressure capacity in the C4 range (up to 3600 Pa) where the site demand requires it. Note the phrase “where the site demand requires it”: a very high rating is only useful if it matches the calculated load, and a very low rating is a defect waiting for a storm.

Glass safety. AS 1288 governs glass selection. In apartments, the critical zones are glazing that could be mistaken for a doorway, glazing below 500 mm above floor level, full-height panels, and glass in doors and side panels. Grade A safety glass — toughened, or laminated with an appropriate interlayer — is generally required in these locations. Balcony doors and large sliding panels deserve particular attention because human impact loads there are both higher and more likely.

Fire and external walls. Replacements must not reduce the fire-resisting construction required between the building and its boundaries or between buildings. Where openings are within the separation distances set out in NCC Section C, the wall — including the window — must achieve the required fire-resistance level. Swapping a rated assembly for an unrated one is a compliance breach even if it looks identical.

Access and egress. Operable windows serving habitable rooms need to satisfy ventilation and, where relevant, egress provisions. In apartments, the interaction between fixed glazing, restricted openings and openable area is often reviewed during the alteration approval, especially for bedrooms relying on natural ventilation.

There is also the existing approval to consider. Conditions of development consent commonly impose acoustic requirements on windows facing a road, rail line or commercial area. Those conditions travel with the building. Replacing an acoustic window with a standard one can breach an ongoing consent condition even if the new window is fully AS 2047 compliant.

5. Acoustic and thermal upgrades: the real reason most owners apply

Most apartment replacement projects are not cosmetic. They are driven by one of four problems: noise intrusion, condensation, heat gain, or failed IGUs. Each has a specific technical answer, and each needs to be evidenced.

Noise. Effective acoustic performance depends on the whole assembly, not only the glass. A laminated panel with a 0.76 mm or 1.14 mm acoustic interlayer, a drained and ventilated cavity, double compression seals, and a frame with no unsealed paths will outperform a heavier single pane in a leaky frame. If the building fronts a busy road, target the acoustic outcome and then select the assembly — and get Rw figures for the assembly as tested, not extrapolated from glass data alone.

Condensation. Fogged IGUs indicate seal failure and are usually a maintenance item for the owners corporation. Interior surface condensation is a different problem: it points to a cold frame, a thermal bridge at the fixing, or excessive internal humidity. Thermally broken aluminium with a polyamide strip, warm-edge spacers and a properly sealed internal air barrier address the first two. Note that tightening a building’s envelope without adding ventilation can move the problem, not solve it.

Heat gain. In apartments, west and north-west glazing is the dominant cooling load. Solar heat gain coefficient matters more than U-value in most Australian climates, and the right answer is often a spectrally selective coating rather than simply thicker glass. In cooler zones, the balance flips toward U-value retention.

Failed units. A fogged IGU in an apartment is a costly item because access is difficult. It is also a chance to upgrade: replacing a 20-year-old unit with a modern low-e, argon-filled unit with a warm-edge spacer delivers a measurable performance step at similar access cost.

6. Installing into an occupied building

The installation plan is a governance document as much as a construction one. Approvals are refused when committees cannot see how disruption will be controlled.

• Access. External access by elevated work platform, swing stage or rope access must be licensed and insured, and may require a separate building or council permit. Internal-only access is sometimes possible for sliding panels but rarely for fixed glazing above ground floor.
• Make-safe. Every opening must be temporarily weatherproofed at the end of each shift. In a multi-storey building a single unsealed opening during a storm can damage several lots.
• Fire and egress. Do not obstruct stairways, corridors or hydrant access. Do not prop fire doors open for material movement.
• Waste and protection. Broken glass, old frames and packaging must be removed daily. Lift and lobby protection should be specified, not improvised.
• Notifications. Written notice to affected lots at least 5 to 7 days ahead, with a named contact and a daily work window, prevents most complaints.
• Water and dust. Cutting and drilling generate fine dust; wet cutting and local extraction should be specified for interior works.

Sequence matters too. Where the existing frames remain, reglazing is faster and cheaper; where frames are replaced, work typically runs one elevation at a time so that each face is closed before the next begins, which also keeps the building’s weather envelope intact.

7. Costs, timelines and what drives them

Indicative ranges help committees budget, but the spread is wide because access dominates. As a rule of thumb for apartment work, expect the following shape rather than a fixed number.

Timelines commonly break down as: 2–6 weeks for the technical pack and engineering; 4–12 weeks for the owners corporation process, including meeting cycles; 4–8 weeks for manufacture; 1–4 weeks for installation depending on opening count. Committees that pre-agree a delegated authority for compliant window replacements remove the single largest delay.

8. The five failure modes to design out

1. Wrong instrument. A committee resolution used where a special resolution was required. The work is later challenged and must be re-approved or reversed.
2. Certificate mismatch. The certificate is for a different size, glazing make-up or fixing condition than what is installed.
3. Missing acoustic condition. The building had a consent condition for acoustic performance; the replacement ignores it.
4. Unsealed fixings. Water tracks past the frame into the wall cavity, appearing as a ceiling stain two floors down.
5. No defect closeout. No water test, no photographic record, no as-built schedule — so responsibility for the first leak cannot be established.

Each is cheap to prevent at documentation stage and expensive to resolve afterwards.

9. Specifying a system that survives the approval process

The fastest route through strata approval is a product with evidence that a certifier, an engineer and a committee can all read without translation. That means an AS 2047 certified system with a traceable licence, a documented design pressure capacity, glass selection calculated under AS 1288, and installation details that show how the frame is fixed and sealed.

Meichen (MC Windows & Doors), trading as MEICHEN Windows & Doors from its Zhaoqing facility in Guangdong, manufactures aluminium window and door systems for Australian and New Zealand projects across 33 series and 48 AS 2047 certified window and door types, with AS 2047:2014 certification under CSI Licence 7708, SNZ TS 4211:2022 certification covering 13 products, S-mark licence 3022 issued through BV, and AGWA membership number 39011. The systems use 2.0 mm wall 6063-T5 aluminium profiles, multi-chamber thermal breaks, three-line EPDM sealing, water resistance to W4 (up to 960 Pa) and wind pressure capacity to C4 (up to 3600 Pa), with acoustic assemblies achieving up to 45 dB reduction, and finishes tested to more than 3000 hours of salt spray. Ultra-slim frames with 18–20 mm visible sightlines support glass-to-frame ratios above 90%, which matters in apartments where daylight and outlook drive value. Frames and IGUs carry 10-year warranties, hardware 10 to 15 years, and project files are retained for 10 years — useful when a scheme needs to match a replacement unit to an original specification years later.

For strata work, ask the supplier for three things beyond the standard certificate: the engineering check against your building’s design pressure at the relevant height, the glass schedule per opening, and a written installation methodology suitable for lodgement. Suppliers who can produce all three quickly are signalling that they have done apartment work before.

Frequently asked questions

Can I replace my apartment windows without owners corporation approval?

In most schemes, no. External windows are commonly common property, and altering common property without approval is a breach of the by-laws and the Act. Even where the window is lot property, changing its appearance or performance often requires approval because it affects the building’s facade and its compliance. Get written confirmation of ownership and the required instrument before ordering anything.

Who pays for the replacement?

It depends on the cause and the by-laws. Where the window has reached the end of its service life or failed through normal deterioration, the cost is usually a common property expense met by the owners corporation, sometimes through a special levy. Where the owner is upgrading for amenity — better acoustics, different colour, larger opening — the owner normally pays, and a by-law commonly records that obligation. Damage caused by an owner’s contractor is recoverable from that owner.

Will a like-for-like replacement still need a new building approval?

Not always, but often something is required. Straight substitution of the same opening type, same dimensions and equal-or-better performance is usually handled as maintenance or a minor alteration, subject to the scheme’s rules and local council requirements. Any change to opening size, frame depth, glazing mass, colour or opening type is an alteration, and may need certifier involvement, an energy check and updated documentation.

How do I prove the new windows meet AS 2047 for my building?

The certificate proves the system was tested; the engineering check proves the system suits your building. You need both. Provide the site’s design wind pressure for the specific height and terrain category, confirm the tested capacity exceeds it, and confirm water resistance matches exposure. Then confirm the installed configuration — size, glass make-up, fixing — matches what was certified.

What is a realistic timeframe from application to completion?

Eight to twenty weeks is typical for a straightforward scheme. The owners corporation process usually takes longer than manufacture. Applications fail or stall most often because the technical pack is incomplete, so the practical way to compress the program is to lodge a complete pack and pre-agree the conditions the committee will want.

Conclusion

Apartment window replacement in Australia is a two-track process: a governance track through the owners corporation, and a technical track through AS 2047, AS 1288 and the NCC’s Class 2 provisions. Owners who run only one track end up with either an approval they cannot build or a building they cannot approve. Run both, document the performance of the assembly as installed rather than as tested, plan access and make-safe before the first panel comes out, and the project becomes predictable — which, in an occupied building, is the outcome everyone is actually voting for.