- Retrofit double glazing keeps your existing frame and swaps the single pane for a sealed insulated glass unit. Typical cost is $450 to $900 per window.
- Full frame replacement removes the entire window and installs a purpose-built double glazed system. Typical cost is $900 to $2,200 per window.
- Retrofit achieves whole-window U-values around 3.0 to 4.5. Full frame uPVC reaches 1.4 to 2.6, because the frame sets the performance ceiling.
- Choose retrofit for sound timber frames, heritage overlays, strata restrictions and staged budgets. Choose full replacement for corroded aluminium, rotted timber, noise problems and renovations.
- Assess the frames first. A retrofit quote on frames needing repair often lands within 15 per cent of full replacement.
If your living room is freezing every July, or the west-facing bedroom becomes unbearable by 4pm, your windows are usually the first place to look. Once you start researching, two options dominate: retrofit double glazing, and full frame window replacement.
Both promise double glazing. They deliver it very differently, cost different amounts, and last different lengths of time. This guide explains how each works in Australian conditions, what they cost, what performance you can realistically expect, and how to tell which one your home actually needs.
Retrofit vs Replacement Windows: The Short Answer
Retrofit double glazing keeps your existing window frame and swaps the single pane for a double glazed unit. Full frame replacement removes the entire window, frame included, and installs a purpose-built double glazed system.
Retrofit costs less and causes less disruption, but its performance is capped by the frame you keep. Full frame replacement costs more upfront and delivers better thermal, acoustic and air-sealing results because the frame, glass and seals are engineered to work together.
| Retrofit Double Glazing | Full Frame Replacement | |
|---|---|---|
| What changes | Glass only | Glass, frame, seals, hardware |
| Typical cost per window | $450 to $900 | $900 to $2,200 |
| Install time per window | 1 to 2 hours | 3 to 5 hours |
| Frame condition required | Sound, no rot or corrosion | Any condition |
| Typical U-value achieved | 3.2 to 4.2 | 1.6 to 2.8 |
| Expected lifespan | 10 to 20 years (limited by host frame) | 25 to 40 years |
| Heritage suitability | Excellent | Requires sympathetic design |
| Best for | Sound timber frames, heritage overlays, staged budgets | Corroded aluminium, rotted timber, renovations, maximum performance |
If your frames are structurally sound and you need to preserve their appearance, retrofit makes sense. If they rattle, stick, leak daylight or show corrosion, you are putting good glass into a compromised system.
What Is Retrofit Double Glazing?
Retrofit double glazing replaces the single pane in your existing window with a sealed insulated glass unit, or IGU. The frame stays exactly where it is.
The process usually involves:
- Removing the original glass
- Modifying the glazing rebate or beads so the thicker IGU will fit
- Installing the new unit with fresh seals and packers
On most jobs, an installer works entirely from inside the room. There is no render patching, no plaster repair, no architrave replacement. You keep the look of your windows, the work is fast, and the cost is roughly half that of full replacement.
The constraint is equally clear. Your original frame was designed to hold a 4mm or 6mm single pane. A retrofit IGU has to fit inside that same rebate, which limits how wide the air cavity can be, and narrower cavities mean less insulation. A standard new double glazed window might carry a 12mm to 16mm cavity. A retrofit into an old aluminium frame is often restricted to 6mm to 8mm.
What retrofit double glazing is not
- Secondary glazing adds a second independent pane inside the existing window, usually in a separate frame. The original glass stays. Different product, different acoustic strengths, different maintenance.
- Piggyback inserts bond a second pane to the existing glass rather than replacing it with a factory-sealed unit. These are prone to internal condensation because the cavity is not hermetically sealed. Reputable Australian installers rarely recommend them.
- True retrofit double glazing removes the original pane entirely and installs a factory-sealed IGU into the modified frame. This is the only version worth comparing against full replacement.
What Is Full Frame Window Replacement?
Full frame replacement removes everything: sash, frame, seals, hardware, back to the structural opening. A new purpose-built double glazed window goes in its place.
Because the frame is new, everything can be specified together:
- The IGU cavity width suits the frame rather than being squeezed into an old rebate
- Warm-edge spacers replace conductive aluminium ones
- Compression seals close against the sash
- Drainage and weep paths are designed for the system
- New flashing manages water at the reveal
Frame material becomes a decision rather than a constraint. Multi-chambered uPVC, thermally broken aluminium and timber composite each behave differently, and you choose based on climate, orientation and exposure. The differences across our window ranges come down to thermal performance, appearance and maintenance.
Full replacement also lets you change the window itself. A fixed pane can become an awning. A sliding window can become a casement for better cross-ventilation. Sill heights can be adjusted to meet current fall-prevention requirements.
The trade-off is disruption. Removing a frame means disturbing plaster, architraves, render or cladding at the reveal. Expect making-good work and a longer install per opening.
Side-by-Side Comparison
Thermal performance
Retrofit improves the glass, and glass is typically 70 to 80 per cent of a window’s area. Upgrading from clear single glazing to a low-E IGU noticeably reduces radiant heat loss in winter and heat gain in summer.
But the frame keeps behaving as it always has. Non-thermally-broken aluminium conducts heat readily. On a 3°C Canberra morning, the frame stays cold even when the glass is warm, so you still get cold edges, cold air dropping off the window, and condensation collecting on the frame rather than the glass. Full frame replacement addresses the perimeter as well as the centre.
Acoustic performance
Noise is where the difference is most often underestimated. Sound leaks through gaps far more readily than it passes through glass. A retrofit IGU into a frame with worn sash seals will help, but the improvement is limited by every gap left in place.
Retrofit can incorporate asymmetric glass thicknesses for sound control, which genuinely works. Full replacement adds compression seals and a tighter overall envelope, and allows laminated acoustic glass with wider cavities. On a Sydney arterial road or under a Canberra flight path, that combination performs more consistently.
Air infiltration, security and lifespan
Retrofit replaces glazing seals only. Sash seals, gaskets, weather stripping and hardware alignment stay as they are. If you can see daylight around a closed sash today, you will still see it afterwards. Full replacement resets air-tightness completely.
Retrofit also keeps existing locks, latches and hinges, working within the original frame strength and hardware positions. Full replacement gives you multi-point locking, new hinges and rollers, and frame sections designed to resist forced entry.
A retrofit IGU typically carries a 10 to 15 year seal warranty, but the unit only lasts as long as the frame holding it. If your aluminium frames are already 30 years old and corroding, the practical life of that investment is shorter than the glass warranty suggests. New windows carry 10 to 25 year warranties with realistic service lives of 25 to 40 years.
Appearance
This is retrofit’s clearest win. From the street, a well-executed retrofit is close to invisible. Glazing beads may look slightly deeper from inside and the glass line sits further back, but original profiles, sightlines and proportions survive intact. On a heritage-listed Adelaide villa or a Paddington terrace, that can be the deciding factor regardless of performance.
Cost Comparison in Australia
Prices vary by product, access, glass specification and installer. The ranges below are planning figures, not quotes.
| Option | Typical range |
|---|---|
| Retrofit double glazing, standard sizes | $450 to $900 |
| Retrofit into heritage timber, custom profiles | $700 to $1,400 |
| Full frame uPVC, standard sizes | $900 to $1,600 |
| Full frame thermally broken aluminium | $1,200 to $2,200 |
| Sliding or stacker doors, full frame | $3,000 to $8,000+ |
For a typical 15 to 20 window home:
- Retrofit throughout: $9,000 to $18,000
- Full frame uPVC throughout: $18,000 to $32,000
- Full frame thermally broken aluminium: $24,000 to $44,000
Broadly, full frame replacement runs 60 to 100 per cent more than retrofit on a like-for-like basis. That gap narrows considerably once frame repairs enter the picture.
The costs most quotes don’t include
- Frame repair discovered on removal. You cannot properly assess a timber frame until the glass is out. Rot behind putty lines, failed joints and soft sills are routinely found mid-job. Repair costs of $200 to $600 per window are common.
- Rebate modification. Some frames need machining to accept an IGU. Others cannot be modified safely at all, which is only established once work has started.
- Making good. Full replacement usually involves plaster patching, architrave replacement, render repair or cladding reinstatement. Budget $150 to $400 per opening. Adelaide bluestone and Sydney double-brick both add cost here.
- Access. Second-storey terraces, narrow setbacks, and anything requiring scaffolding or a crane can add $1,500 to $5,000. Neither method escapes this.
- Disposal. Old aluminium frames and glass removal generally add $30 to $80 per window.
The practical lesson: a retrofit quote on frames that turn out to need repair often lands within 15 per cent of a full replacement quote, while delivering a fraction of the performance and a shorter service life. Insist on a physical inspection before committing either way.
Performance: What the Numbers Show
Australian windows are rated through the Window Energy Rating Scheme (WERS), which publishes U-value and Solar Heat Gain Coefficient (SHGC) for tested products.
U-value measures heat transfer through the whole window, frame included. Lower is better.
SHGC measures how much solar radiation passes through, on a scale of 0 to 1. Lower means less summer heat gain. Higher means more free winter warmth.
| Configuration | U-value |
|---|---|
| Single glazed, aluminium frame | 6.2 to 7.5 |
| Single glazed, timber frame | 4.8 to 5.6 |
| Retrofit IGU, existing aluminium frame | 3.6 to 4.5 |
| Retrofit IGU, sound timber frame | 3.0 to 3.8 |
| Full frame uPVC, standard IGU | 1.8 to 2.6 |
| Full frame thermally broken aluminium | 2.2 to 3.0 |
| Full frame uPVC, low-E argon-filled IGU | 1.4 to 2.0 |
Two things stand out. First, retrofit delivers a genuine improvement. Going from 6.5 to 4.0 is roughly a 38 per cent reduction in heat transfer, and you will feel it.
Second, the frame sets the ceiling. Retrofit into old aluminium tops out around 3.6 no matter how good the glass is, because the frame is a thermal bridge running around the entire perimeter. Full frame uPVC reaches 1.8 or better.
NCC 2022 lifted new-home requirements to NatHERS 7 stars, and Section J sets thermal performance requirements for building fabric including glazing. These apply to new builds and significant renovations rather than voluntary upgrades, but they set the benchmark. Ask any installer for the WERS-rated U-value and SHGC of the specific configuration quoted, not the glass alone.
When Retrofit Double Glazing Is the Right Choice
- Your timber frames are sound. Well-maintained hardwood joinery with no rot, tight joints and smooth operation often has decades of life remaining and better inherent thermal performance than aluminium.
- A heritage overlay restricts change. Where councils require original joinery to be retained, retrofit is frequently the only compliant route to double glazing.
- Strata rules limit façade alterations. Retrofit preserves sightlines and profiles, which makes approval far more likely.
- You are staging a budget. Retrofitting the worst rooms now gets you comfort improvements this winter rather than in three years.
- You are not staying long. If you expect to sell within five to seven years, the payback case for full replacement weakens.
- Access is genuinely difficult. Where frames sit behind cladding or fixed external treatments, removal may be impractical enough to change the calculus.
When Full Frame Replacement Is the Better Investment
- Your frames are non-thermally-broken aluminium. This covers most Australian homes built between 1970 and 2005. These frames conduct heat aggressively and undermine any glass you put in them.
- There is corrosion, rot or distortion. Pitting, white powdery oxidation, soft sills, springy timber, or frames that move under hand pressure all indicate end of service life.
- Windows stick, jam or rattle. Symptoms of racked frames or worn hardware. New glass fixes neither.
- You can see daylight around closed sashes. Air infiltration at that scale defeats most of the benefit of better glass.
- You are already renovating. Making-good costs are largely absorbed by work you are doing anyway. This is the single best time to replace windows.
- You want to change the window itself. Different opening style, sill height, larger opening, better ventilation.
- Noise is the primary problem. Air-tightness matters as much as glass, and only full replacement resets it.
How to Assess Your Existing Windows: A 7-Point Check
Walk your home with this list. It takes about twenty minutes.
- Identify the frame material and age. Aluminium with no visible plastic strip between inner and outer sections is non-thermally-broken. Timber, check for painted-over rot. uPVC, check for yellowing or brittleness.
- Test for rot and corrosion. Press a screwdriver handle firmly into timber sills. Softness means rot. On aluminium, look for pitting, white powder or loose fixings, particularly on coastal elevations.
- Check for daylight gaps. Close the window fully, turn off the lights and look around the sash perimeter. Visible daylight means air infiltration.
- Do the rattle test. Push the closed sash with your palm. Movement means worn seals, worn hardware or a racked frame.
- Inspect the sill. Water stains, paint bubbling, dark patches or spongy sections indicate water is getting in and sitting.
- Test operation. Sticking, jamming or requiring force means the frame has moved or hardware has failed.
- Check sash seals. Hard, cracked, flattened or missing seals mean the window is not sealing regardless of what glass is in it.
Reading your results:
- Zero to one issue across most windows: retrofit is viable.
- Two to three issues: get a professional assessment before committing.
- Four or more, or any structural rot or corrosion: retrofit is putting new glass into a failing system.
Retrofit vs Replacement in Adelaide, Sydney and Canberra
Adelaide
Adelaide sits in NCC climate zone 5, with hot dry summers and cool winters. Cooling load usually dominates, which makes SHGC the more important number. West and north-west facing windows on a 40°C February afternoon are the priority.
The housing stock splits sharply. Bluestone and sandstone villas across Norwood, Unley, Prospect and North Adelaide carry original timber joinery, frequently under heritage overlay. Where that joinery is sound, retrofit is often both compliant and sensible.
Post-1970 aluminium stock in the northern and southern suburbs is a different case. Non-thermally-broken frames plus Adelaide summers is the weakest possible combination. Our replacement windows for Adelaide homes are specified with SHGC ratings suited to zone 5 cooling loads. Note that removing glass from bluestone or double-brick openings requires care, and making-good costs sit at the higher end.
Sydney
Sydney spans climate zones 5 and 6, with three specific complications.
Strata and owners corporations. Windows are often common property. Under NSW strata legislation, alterations to common property generally require a special resolution. Retrofit, which preserves external appearance, is far more likely to be approved. Check your by-laws before getting quotes.
Heritage conservation areas. Paddington, Balmain, Glebe, Newtown, Annandale and large parts of the inner west sit within conservation areas restricting changes to street-facing windows. A common outcome is retrofit to front elevations, full replacement to the rear.
Coastal exposure. Bondi through to Manly and the northern beaches expose aluminium to salt-laden air. Corrosion, pitting and seized hardware are widespread. Our Sydney replacement windows include finish and hardware options rated for salt exposure.
Traffic noise on Parramatta Road, Victoria Road, the Princes Highway and under flight paths also pushes toward full replacement.
Canberra
Canberra is climate zone 7, the coldest capital in the country, with a heating season running April to September. This is where the thermal case is strongest and U-value dominates.
Condensation is the giveaway. Single glazed aluminium in Canberra runs with water on the frames most winter mornings, causing mould at reveals, damaged plaster and rotted sills over time. Retrofit warms the glass but the aluminium frame stays cold and keeps sweating. Full frame uPVC addresses both surfaces.
Much of Canberra’s stock is post-1970 aluminium, poorly suited to retrofit. Older red brick stock across Ainslie, Yarralumla, Reid and Braddon has timber joinery worth assessing individually. The gap between a U-6.5 single glazed window and a U-1.8 uPVC window across a 26-week heating season is where full replacement makes the clearest financial case in Australia. See how we work across our Canberra service area for zone 7 conditions.
Heritage, Strata and Council Considerations
- Heritage listings and overlays. Commonly require original joinery to be retained or replaced like-for-like. Retrofit is frequently permitted where full replacement is not, though slim-profile heritage-styled systems are sometimes approved. Ask your council’s heritage adviser first.
- Conservation areas. Broader than individual listings, typically controlling street-facing elevations only.
- Strata schemes. Window frames are usually common property. In NSW, alterations generally require a special resolution. SA and ACT community and unit title schemes have parallel requirements. Get approval in writing before ordering.
- Development approval. Like-for-like replacement is usually exempt development. Changing opening sizes or altering the façade in a heritage area may require DA.
- Bushfire attack level (BAL). In bushfire-prone areas across the Adelaide Hills, greater Sydney and the ACT fringe, windows must meet AS 3959. Full frame replacement makes compliance simpler because the entire system can be BAL-rated. Retrofit glass does not automatically make a window compliant.
Can You Mix Both Methods?
Yes, and it is often the smartest approach. A common pattern is full frame replacement to the worst elevation, usually west or the noisiest street frontage, with retrofit to secondary bedrooms and rear rooms where frames are sound.
- Sequence by discomfort, not convenience. Start with the rooms you avoid.
- Lock in appearance decisions upfront. Frame colour, sightline width and glazing bead profile should be decided at stage one, even if stage three is four years away. Product ranges change.
- Get one assessment, not three. A single whole-of-house inspection produces a more coherent plan than three separate quotes over five years.
Warranties, Lifespan and Resale Value
Retrofit warranties typically cover the IGU seal for 10 to 15 years and workmanship for 1 to 7 years. The critical exclusion is the host frame. If your timber frame moves and stresses the unit, or your aluminium frame corrodes around it, that is generally not covered.
Full frame warranties typically run 10 to 25 years covering the complete system: frame, glass, seals and hardware, with a single point of accountability.
Resale. Double glazing is an increasingly visible selling point in Canberra particularly, where buyers actively ask about it. Full replacement is more visible to buyers and more defensible in a building inspection, since retrofit into an old frame will still show frame-condition issues in the report.
Getting the Right Advice for Your Home
There is no universal answer. There is a right answer for your specific frames, your climate zone, your planning constraints and how long you intend to stay.
What consistently produces good outcomes is assessing the windows properly before choosing a method, rather than choosing a method and hoping the windows suit it. Oknalux works across Adelaide, Sydney and Canberra on both retrofit double glazing and full frame replacement, which means the assessment comes before the recommendation. Book a free consultation to have your existing windows assessed before you commit.
Frequently Asked Questions
What is the difference between retrofit and replacement windows?
Retrofit double glazing replaces only the glass, installing a sealed insulated glass unit into your existing frame. Full frame replacement removes the entire window, including frame, seals and hardware, and installs a new purpose-built double glazed system. Retrofit costs roughly half as much but is limited by the performance of the frame you keep.
Is retrofit double glazing as good as replacement windows?
No. Retrofit typically achieves a whole-window U-value of 3.0 to 4.5, while full frame uPVC reaches 1.4 to 2.6. The frame sets the ceiling, because non-thermally-broken aluminium conducts heat around the entire perimeter no matter how good the glass is. Retrofit still delivers a genuine improvement over single glazing, roughly a 38 per cent reduction in heat transfer.
Will double glazing stop condensation?
It substantially reduces condensation by raising the internal surface temperature so moisture is less likely to condense. It does not eliminate it. If your home generates a lot of moisture through drying laundry indoors, unflued gas heating or poor bathroom ventilation, you will still see condensation on the coldest surfaces. Retrofit into aluminium frames often just relocates the problem from the glass to the frame.
Can every window be retrofitted?
No. Frames with rebates too shallow to accept an IGU, frames with rot or corrosion, some steel-framed windows, curved or leadlight windows, and certain proprietary systems either cannot be retrofitted or cannot be retrofitted economically. Where rebate modification approaches the cost of a new window, retrofit stops making sense.
Do I need council approval to replace my windows?
Usually not for like-for-like replacement, which is generally exempt development. You likely do if your property is heritage listed or in a conservation area, if you are changing opening sizes or façade appearance, or if you are in a strata scheme where owners corporation approval is required.
Is retrofit double glazing a realistic DIY project?
No. IGUs are heavy, fragile, and must be installed with correct packing, setting blocks and drainage to prevent seal failure. Incorrect installation voids the manufacturer’s warranty and typically causes the unit to fog within a few years. Both methods should be professionally installed.
Disclaimer: This guide provides general information only. Window performance, retrofit suitability, pricing and installation requirements vary significantly between products, home designs, building regulations and climates. Pricing figures are indicative market ranges as at 2026 and are not quotes. Always seek advice specific to your property, local conditions and any applicable council, heritage or strata requirements before proceeding with window upgrades.
