Retrofit double glazing means fitting double glazed glass into the window frames you already have, instead of replacing the whole window. As of October 2026, What’s The Damage puts retrofit double glazing into sound single-glazed frames at about $400 to $1,200 per window (typical $750, including GST), while the NSW Government gives $600 to $2,000 or more per new double glazed window installed. Both are indicative only.
- What’s The Damage (October 2026): retrofit double glazing costs about $400 to $1,200 per window, with a typical job around $750 including GST.
- Retrofit only works when the existing frames are sound and deep enough to hold a thicker double glazed unit.
- Secondary glazing adds a second pane inside the window. YourHome says it can give good noise control but will not insulate as well as a sealed unit.
- In the WERS figures on YourHome, a single glazed aluminium window has a U-value of 6.9, double glazed aluminium 4.2 and double glazed timber or uPVC 3.0. Lower is better.
- In NSW strata buildings, installing double or triple glazed windows is a minor renovation that needs owners corporation approval.
What is retrofit double glazing?
Retrofit double glazing is when a glazier takes the single pane out of your existing frame and fits a double glazed unit in its place. A double glazed unit is two panes of glass sealed together with a gap of air or gas between them.
The term is used loosely, so check what each company means. Some businesses sell secondary glazing, a separate pane of glass or acrylic fitted inside your window, and call it retrofit double glazing. Both can help, but they are different products with different results.
YourHome, the Australian Government’s sustainable home guide, says the gap in a sealed unit is usually 6 to 18 mm, with 12 mm normally preferred. That makes the glass much thicker than a single pane, which is why the frame matters so much.
Retrofit glass vs secondary glazing vs new windows: which is right?
The right choice depends on the state of your frames, your budget and whether you need to keep the look of the window. Here is how the four common options compare.
| Option | What is done | Indicative cost | Best for | Watch out for |
|---|---|---|---|---|
| Retrofit double glazing | Single pane replaced with a sealed double glazed unit in the existing frame | About $400 to $1,200 per window, typical $750 (What’s The Damage) | Sound timber or aluminium frames with room for thicker glass | The frame stays the same, so a plain aluminium frame still loses heat |
| Secondary glazing | A second pane of glass or acrylic fitted inside the existing window | About $400 per m² (Airtasker, 2024); no current Sydney per-window figure found | Heritage homes and apartments where the outside of the window must not change | Not fully sealed, so it insulates less than a sealed unit |
| Replace a failed double glazed unit | Foggy or leaking sealed unit swapped for a new one | About $300 to $1,200 per window (What’s The Damage) | Double glazing that has gone cloudy between the panes | Check the frame and drainage at the same time |
| New double glazed windows | Whole window, frame and glass, removed and replaced | About $600 to $2,000 or more per window installed (NSW Government) | Rotten, rusted, warped or leaking frames, or a change of style | Making good around the frame, and approval if the opening changes |
Sources: What’s The Damage glazier cost Sydney (updated October 2026, includes GST); NSW Climate and Energy Action (updated July 2026); Airtasker double glazed windows cost guide (updated July 2024). Indicative only.
How much does retrofit double glazing cost in Sydney?
Expect about $400 to $1,200 per window for retrofit double glazing, based on What’s The Damage’s Sydney glazier guide, updated October 2026. Its typical figure is $750 per window, and prices include GST.
The same guide puts whole-home reglazing or double glazing at about $8,000 to $40,000, with a typical job around $18,000. Its Sydney and national tables show the same figures, so treat them as a national guide rather than Sydney-only prices.
Other sources run higher for full new windows. The NSW Government says new double glazed windows cost $600 to $2,000 or more per window installed. Windows Republic, a Melbourne uPVC window maker, puts double glazed windows at about $2,200 to $3,800 per window fully installed. The sources disagree, so get itemised quotes.
The main things that change the price are:
- Window size and number of windows
- Glass type: clear, low-e, toughened or laminated for safety or noise
- Whether the frame needs repairs, new glazing beads or other changes to take the thicker unit
- Access: upper-storey windows and large panes take more labour
- Odd shapes, leadlight or coloured glass
For prices on full window replacement, read our guide Double Glazed Windows Cost Sydney: 2026 Price Guide.
What frames suit retrofit double glazing?
Frames suit retrofit when they are straight, solid and deep enough to hold a double glazed unit. A glazier should check every window before quoting.
- Timber frames: often good candidates if the timber is sound. Rot, loose joints or sashes that stick should be fixed first, or the window replaced.
- Aluminium frames: can take retrofit units in some systems. YourHome warns that aluminium conducts heat well and lowers the insulating value of the glass unless the frame is built to reduce this, for example with a thermal break.
- Steel frames: YourHome says some steel frames are set up for double glazing with thermal breaks. Older, slim steel frames may have little room for thicker glass, so ask.
- Old timber sash windows: the sashes are counterbalanced for their current weight. Two panes weigh more than one, so ask whether the balances, cords or springs need changing.
The NSW BASIX default window data shows why the frame matters. An aluminium window with single clear glass is rated at a U-value of 6.7. Double glazing it with clear glass brings that to 4.8. A thermally broken aluminium frame with the same glass is 3.6, and timber or uPVC is 3.0. Lower numbers insulate better.
Does double glazing reduce noise?
Yes, but it helps most with voices and other mid to high-pitched sound. YourHome says sealed double glazing reduces medium to high-frequency noise such as the human voice. For low rumbles like traffic and planes, it recommends thicker or laminated glass, ideally double glazed with the largest air gap possible.
The size of the gap is key. Viridian Glass says the largest gap in a sealed double glazed unit is about 22 mm, and that a gap of 50 to 200 mm makes a substantial difference. That wide gap is what secondary glazing can give, because the second pane sits well inside the first.
| Glazing set-up | Sound insulation (dB) |
|---|---|
| Single glazed, 3 mm glass | 23 |
| Single glazed, 6 mm glass | 27 |
| Double glazed, narrow 8 to 13 mm gap | 31 |
| Double glazed, wide 100 to 125 mm gap | 38 |
Source: Magnetite noise reduction page, citing CSIRO sound insulation research by John Davy. Higher numbers block more sound. Results depend on the whole window and how well it seals.
Every extra decibel helps, but the ear does not hear it in a straight line. Viridian says each 10 dB reduction sounds about half as loud. It also warns that gaps and air leaks in old frames let a lot of noise through, so sealing matters as much as the glass.
In Viridian’s own product data, its ComfortHush laminated glass gives about a 6 dB improvement over ordinary 3 mm glass. If noise is your main problem, ask each installer for the tested rating of the whole window they are quoting.
Is retrofit double glazing worth it in Sydney?
It is often worth it for noisy streets, flight paths and rooms that get very hot or cold, and less so if your windows are small or your frames need replacing anyway.
YourHome says up to 40% of a home’s heating energy can be lost, and up to 87% of its heat gained, through windows. The NSW Government says double glazing makes a house quieter, warmer in winter and cooler in summer, and that some homes may save $500 or more a year on heating and cooling. Your own savings will depend on your home.
| Window type | U-value (Uw) | Solar heat gain (SHGCw) |
|---|---|---|
| Aluminium, single glazed, 3 mm clear | 6.9 | 0.77 |
| Timber or uPVC, single glazed, 3 mm clear | 5.5 | 0.69 |
| Aluminium, double glazed, 3/6/3 clear | 4.2 | 0.69 |
| Timber or uPVC, double glazed, 3/6/3 clear | 3.0 | 0.61 |
Source: YourHome glazing page, using Window Energy Rating Scheme (WERS) data. Lower U-value means less heat lost or gained through the window. Lower SHGC means less summer sun heat comes in.
Sydney winters are mild compared with Canberra or Melbourne, so many Sydney owners choose double glazing for noise and summer comfort rather than heating bills. For hot west-facing rooms, ask about low-e glass with a lower SHGC as well.
The NSW Government says there is currently no Australian Government rebate for double glazed windows. It points to the NSW Home Energy Saver program, which offers zero-interest loans to eligible households. Check the current rules before you count on it.
Heritage homes, apartments and NSW rules
Most retrofit jobs need no council approval, but heritage homes and strata apartments have extra steps.
- Heritage: replacing glazing like for like is often exempt development if it meets the set standards. Work on a heritage item or in a heritage conservation area may need approval. Secondary glazing sits inside the window and can usually be removed, which is why it is often considered for heritage homes. Ask your council before you order.
- Apartments: NSW strata rules list double or triple glazed windows as a minor renovation. You need approval from the owners corporation, usually by a vote with more than 50% of votes cast in favour, before work starts. Windows are often common property, so talk to your strata manager early.
- Licence: in NSW, glazing work worth more than $5,000 in labour and materials (including GST) needs a contractor licence. The NSW Government’s definition of glazing covers installing glass, acrylic or similar materials in windows.
Before you pay a deposit: check the glazier’s licence on verify.licence.nsw.gov.au, get a written contract for work over $5,000 including GST, and pay no more than 10% up front. For work over $20,000, the contractor must give you a Home Building Compensation certificate before taking any payment, and you get five clear business days to cool off.
Get quotes from vetted local glaziers
Describe your windows to MyTradeCrew: how many there are, roughly how big, the frame type and whether noise, heat or draughts bother you most. We will send your job to up to three vetted, licensed and insured local glaziers and window trades from our crew. They quote and contract with you directly, and it is free for homeowners.
Frequently asked questions
Is secondary glazing as good as double glazing?
It depends on the goal. YourHome says secondary glazing will not insulate as well as a factory-sealed double glazed unit, because the edges cannot be fully sealed. But it can give good noise control, because the gap between the panes can be much wider than in a sealed unit. For noise on a busy road, it is often worth comparing both.
Does argon gas in double glazing make a difference?
A little. Viridian Glass says using argon in a 12 mm gap improves the insulating value by about 6% compared with air. It is a modest gain, so ask for the whole-window U-value with and without argon and weigh the price difference. Low-e coatings usually make a bigger difference to heat flow than the gas fill.
Does a glazier need a licence for retrofit double glazing?
Yes, if the job is worth more than $5,000 in labour and materials including GST. In NSW, glazing work includes fitting glass or acrylic into windows, so it covers retrofit units and many secondary glazing systems. Check the licence on the NSW Government’s Verify NSW register and make sure the name matches your quote.
Can I double glaze just some of my windows?
Yes. Many owners start with the rooms where noise or heat is worst, such as bedrooms facing a main road or a west-facing living room. Glaziers price each window separately, so you can stage the work. Ask for a quote that lists every window, so later rooms can be added at a similar price and specification.
Is there a rebate for double glazing in NSW?
The NSW Government says there is currently no Australian Government incentive or rebate for double glazed windows. It lists the NSW Home Energy Saver program, which offers zero-interest loans for some energy upgrades to eligible households. Eligibility rules apply and can change, so check the NSW Climate and Energy Action website before you sign a contract.
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