Retrofit double glazing is the process of replacing the single glass pane in your existing window frames with a sealed insulating glass unit (IGU). The frame, hardware, and sash stay exactly as they are. Only the glass changes.
For Melbourne homeowners weighing up the decision, this guide covers actual costs, thermal payback calculations, noise reduction figures, and property value effects — without the vague "you'll love it" sales copy.
What It Costs
Honest supply-and-install pricing for retrofit double glazing in Melbourne:
| Glass type | Price range (per m²) |
|---|---|
| Standard clear float IGU | $495 – $580 |
| Low-E (hard coat) | $560 – $680 |
| Low-E (soft coat, argon fill) | $620 – $750 |
| Acoustic laminated | $650 – $850 |
A mid-size Melbourne home with 15–20m² of window area typically costs $8,500–$14,000 for a whole-home retrofit. The Instant Estimate tool gives you a figure in 60 seconds based on your actual window dimensions.
Thermal Performance: The Real Numbers
A standard single-pane glass window has a U-value of around 5.8 W/m²K — meaning it loses heat rapidly in winter and conducts it inward in summer.
A double glazed IGU with Low-E coating drops that to 1.4–1.8 W/m²K — a 3× to 4× improvement.
In practice: rooms that previously lost warmth overnight hold temperature until morning. Air conditioning that ran for six hours in summer now runs for three.
Payback Period
For a Melbourne home spending $3,000–$4,000 per year on heating and cooling, a whole-home retrofit typically achieves:
- 10–20% reduction in heating/cooling load from improved U-values
- Annual saving of $400–$800 depending on house size and current leakage
- Payback from energy savings alone: 12–18 years
That figure sounds long. But it ignores two things: noise reduction (hard to put a number on) and property value uplift (not hard to put a number on).
Noise Reduction
Standard double glazing (two 4mm panes, 12mm cavity) achieves an Rw rating of around 30–34. Acoustic laminated IGUs reach Rw 40–44.
For context: a 10 dB reduction is perceived as roughly halving the loudness. Going from Rw 28 (typical single pane) to Rw 40 is a substantial, audible change — particularly for mid-frequency road traffic and tram noise.
Read more: Best glass for noise reduction in Melbourne
Property Value Effect
Multiple Australian property studies have found double glazing adds 3–8% to resale value for residential properties. On a $900,000 home, that range represents $27,000–$72,000.
The average whole-home retrofit cost of $8,500–$14,000 sits well below the lower bound of that range. The investment case is strong, independent of energy savings.
Retrofit vs Full Replacement
Retrofit into existing frames costs roughly 40–60% less than full window replacement for equivalent thermal performance. For timber heritage frames, replacement often isn't even an option under heritage overlays.
See the full comparison: Retrofit vs full window replacement
When Retrofit Isn't the Right Answer
Retrofit has limits. If your frames are structurally compromised — rotted timber, cracked aluminium extrusions, failed seals causing condensation inside the frame — replacement is unavoidable.
Similarly, if your rebate depth is less than 14mm, some IGU configurations may not fit without frame modification. A site assessment confirms this in minutes.
Getting a Price
The Double Glazing Cost page has full pricing breakdowns. Or use the Instant Estimate tool to enter your window count and size and get a transparent, itemised figure before committing to anything.
No site visit required. No sales call. The number you get is the number on the invoice.
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