Window frames showing oxidation, weatherseals shrinking and failing, persistent leaks that repairs alone cannot fix — when these problems appear together, a full window replacement is often the only lasting solution. Yet many owners find it difficult to estimate the cost: how much does one window cost to replace? How should a full-flat budget be calculated? Is frame-in-frame installation or full frame removal the better approach? This guide breaks down the key factors affecting replacement costs, 2026 market price references, and declaration requirements, so you can budget accurately and avoid unexpected expenses.
5 Key Factors That Affect Aluminium Window Replacement Costs
Window replacement costs are not a fixed figure — they depend on a range of variables. Understanding these five factors will help you estimate your budget accurately and avoid overspending.
1. Aluminium Profile Grade Profile thickness is typically measured in millimetres, with 40mm and 50mm being the most common grades. 50mm aluminium is structurally stronger and suited to larger window openings; 40mm is commonly used for standard residential windows. The thicker the profile, the more aluminium material is required, and the higher the cost.
2. Glass Selection Single-pane glass is the most affordable option but offers limited soundproofing and thermal insulation. Double-glazed insulating glass costs more but delivers noticeably better noise reduction — particularly valuable for units near busy roads or train lines. Tempered glass is also available for enhanced safety, at a higher price point.
3. Installation Method: Frame-in-Frame vs Full Frame Removal The installation method is one of the most significant cost factors, explained in detail below. Frame-in-frame installation fits a new window inside the existing frame with minimal disruption and lower cost; full frame removal takes out the old frame entirely and reinstalls from scratch, which involves greater labour and higher cost.
4. Window Size and Quantity Larger window openings require more aluminium and glass, which increases material costs. For full-flat replacements involving multiple windows, some contractors offer package pricing — it is worth requesting a combined quote rather than pricing each window separately.
5. Scaffolding For higher-floor units where external wall work requires scaffolding, the scaffolding cost can be substantial. Always confirm during the quotation stage whether scaffolding is included in the quoted price.
2026 Hong Kong Window Replacement Cost Reference
The following ranges reflect general market pricing. Actual costs depend on building conditions, window dimensions, and installation complexity — an on-site assessment is needed for an accurate quote.
| Item | Reference Cost |
|---|---|
| 40mm single-glaze aluminium window (materials + labour) | From $160–$200 / sq ft |
| 50mm single-glaze aluminium window (materials + labour) | From $200–$250 / sq ft |
| Double-glazed insulating glass window (materials + labour) | From $280–$350 / sq ft |
| Old frame removal | From $1,000–$2,000 / window |
| Scaffolding | From $2,500 (floor-dependent) |
| Mandatory window inspection & Class 2 Minor Works declaration | From $250 |
Important: Full aluminium window replacement is classified as a Class 2 Minor Works project under Hong Kong building regulations. A licensed contractor registered with the Buildings Department must submit the declaration on your behalf. Amgen Windows holds licence number MWC 316/2021 and handles all declaration procedures. For full details of what is included, visit our window replacement services page.
Frame-in-Frame vs Full Frame Removal: Which Is Right for You?
These are the two most common window replacement methods in Hong Kong, with a clear difference in cost and scope. The right choice depends on the condition of your existing frames.
Frame-in-Frame Installation This method fits the new aluminium frame directly inside the existing old frame, without removing it. Installation is simpler, quicker, and causes minimal disruption to surrounding walls and finishes — making it the lower-cost option. Because the old frame is retained, the usable window opening is slightly reduced, though the impact on light and ventilation is generally minimal.
Best suited when: the existing frame is structurally sound without serious loosening; the owner wants to minimise disruption and installation time; budget considerations make controlling replacement cost a priority.
Full Frame Removal This method removes the old frame entirely down to the structural wall before installing a new frame. It involves more labour and takes longer, but fully preserves the original window opening size and allows for more thorough waterproofing and sealing between the new frame and the wall structure. If the existing frame has suffered severe oxidation or structural deformation, full removal is often the more reliable long-term choice.
Best suited when: the existing frame has severe oxidation or deformation that cannot support a new window; the owner wants to maximise the window opening area; the works are being carried out alongside a full renovation.
Real Case Study: Tsuen Wan Private Flat Owner Replaces All Windows
A private flat owner in Tsuen Wan, in a building over thirty years old, contacted Amgen after noticing that oxidation had spread across multiple window frames throughout the flat, with weatherseals shrinking and failing — causing varying degrees of water ingress every time it rained. The owner was planning a full renovation and wanted to replace all windows at the same time.
After an on-site assessment, our team found that several window frames were still structurally sound and well-suited for frame-in-frame installation, allowing new windows to be installed without disturbing the surrounding finishes. A number of larger windows near the external wall, however, had suffered severe oxidation and were recommended for full frame removal to ensure effective long-term waterproofing. Our team provided itemised quotes for each window, clearly indicating the recommended method and cost breakdown, so the owner could prioritise accordingly.
The owner chose to complete all replacements in one visit. All works complied with the Buildings Department's Class 2 Minor Works declaration requirements, with Amgen handling the complete documentation process. The entire job was completed in two days, and after completion the windows were fully watertight with noticeably improved noise reduction.
Frequently Asked Questions
Does window replacement require a Buildings Department declaration?
Yes. Full aluminium window replacement is classified as a Class 2 Minor Works project, and must be declared to the Buildings Department by a licensed contractor. Failing to file the required declaration can cause complications when selling the property or during future mandatory window inspections. Amgen Windows holds licence MWC 316/2021 and handles the complete declaration process on your behalf — owners simply need to provide their personal documents.
Does the window replacement quote include scaffolding?
Not necessarily. Scaffolding is typically charged separately and depends on floor height and the scope of the works. Most lower-floor units (fifth floor and below) can have windows replaced from inside the flat without scaffolding; higher floors or large-scale external wall works require separate assessment. Our team will clearly advise during the on-site assessment whether scaffolding is required and what the associated cost would be — no hidden charges.
How long does a full-flat window replacement take?
It depends on the number of windows and the installation method. For a typical three-bedroom flat using the frame-in-frame method, the job can generally be completed within one to two days. Cases involving full frame removal or larger windows may extend to two to three days. If scaffolding is required, the time for erecting and dismantling the scaffold must be factored in separately. Our team provides a clear project schedule after the on-site assessment.
Ready to Replace Your Windows? Start with a Free On-Site Assessment
Aluminium window replacement costs vary considerably depending on building conditions, window specifications, and the installation method — online price guides are only a rough reference, and an on-site assessment is the only way to obtain an accurate quote. If you are considering full-flat window replacement, WhatsApp us at 6586 3435 to arrange a free assessment. Our team will inspect your windows on-site, recommend the most suitable replacement approach, and provide a clear, transparent quotation.
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