The real price lives in the opening, not the frame
A useful benchmark is the aluminum window replacement cost guide, but the number on the first page of a quote is never the full story. In Australian homes, a standard supply-and-install replacement might sit around A$600 to A$1,500 per window, yet the final invoice can move sharply once the old frame comes out and the wall starts telling the truth.
The reason is simple: the window unit is visible before the job starts. The opening is not. The opening can hide softened timber, failed flashing, corrosion, uneven masonry, asbestos-containing linings, or damage from years of water ingress. A contractor can estimate the visible part with confidence. The part behind the plaster or render is where budgets usually break.
What a basic quote usually covers
A proper replacement quote should cover the new frame, glazing, standard labor, removal of the old unit, sealing, and a basic finish. That sounds complete until the actual site conditions appear. On a clean ground-floor swap in a modern home, the job may stay close to the quote because the opening is square, the structure is sound, and access is easy.
That is the exception, not the rule in older housing stock.
The moment a quote says “supply and install,” it is worth asking a harder question: supply and install what, exactly? A bare frame and glass? Or a finished opening ready for paint, with disposal, trimming, patching, and weatherproofing included? Two quotes can show the same headline price while covering very different scopes.
Where the final invoice grows
The cost creep usually comes from five places.
- Trim and reveal repair: Removing an old aluminum frame often chips plaster, breaks internal architraves, or leaves uneven edges. Budget A$100 to A$300 per opening if repainting or patching is needed.
- Weatherproofing and flashing: Old membranes or degraded sealant may need replacement before the new window can go in. That can add A$80 to A$200 per opening.
- Structural remediation: Rot in timber studs, corroded lintels, or damaged masonry can add A$200 to A$800 per affected opening, sometimes more if the damage spreads beyond the immediate frame.
- Access equipment: Second-story work, steep sites, or narrow side access can require scaffolding or an elevated work platform. That often adds A$300 to A$1,200 to the project, not just the window.
- Hazardous materials and compliance: Asbestos, lead paint, permits, and inspection fees can turn a straightforward replacement into a regulated job. A single affected opening can absorb A$500 to A$2,000 before the new window is even installed.
Those are not “extras” in the casual sense. They are the cost of making the opening sound, safe, and code-ready. A quote that excludes them is not cheaper; it is incomplete.
Why older homes see the biggest swings
The worst surprises usually show up in homes built before the 1990s. Frame removal in those properties often exposes the exact problems the original window was hiding. Timber weatherboards can be rotten behind the frame. Render can crack when the old unit is pulled. Brick veneer can reveal mortar breakdown or damaged cavity details. Even when the window size stays the same, the opening may need rebuilding before a new frame can sit properly.
That is why the same style of aluminum window can cost very different amounts on two neighboring houses. One opening is clean and square. The other needs patching, leveling, and a waterproofing fix before installation can begin. The product is the same. The labor is not.
A realistic example of how quotes change
Picture three bedroom windows on the second floor of a brick home.
The first quote says A$3,300, or A$1,100 per window. It includes the frames, install, and basic sealing.
The second quote is A$3,900. Higher at first glance, but it includes scaffold hire and old-frame disposal.
The third quote lands at A$4,600 after the installer discovers damaged reveals and adds patching, repaint prep, and a minor flashing repair.
Only one of those numbers reflects the actual job. The cheapest quote is not automatically the best value if it leaves out the things that make the installation last.
The fastest way to avoid overpaying
The safest budget is built from scope, not guesswork. Before signing anything, every quote should answer the same set of questions:
- Is removal of the old frame included?
- Is disposal of waste included?
- Are internal trims, architraves, and reveal patching included?
- Is external flashing or waterproofing included?
- Are access costs, scaffolding, or elevated platform hire included?
- Are permits, inspections, asbestos checks, or lead-paint work excluded or allowed for?
- What happens if the opening is not square or the substrate is damaged?
If those items are not written down, they usually reappear later as variation charges.
A sensible contingency is 15% to 20% above the quote total, with the higher end reserved for older homes, upper-storey work, or any property that has already shown signs of water damage. That buffer does not mean the installer is overcharging. It means the job has not been fully uncovered yet.
The real savings come from forcing a quote to describe the opening as thoroughly as it describes the window. Once the scope is explicit, price comparisons become meaningful. Until then, the cheapest number is often just the most optimistic one.
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