Yes, you can double glaze existing windows in three ways. You can retrofit a sealed double glazed unit into the current frame, add secondary glazing to the inside, or replace the whole window with a new double glazed one. In most Perth homes with single glazed aluminium frames, full replacement gives the biggest gain because the old metal frame keeps leaking heat whatever glass sits in it.
This guide explains how each method works and why the frame decides the result. It covers which frames suit retrofit, how to check your own windows and what each option costs in Perth. It also explains what changes for heat, noise and condensation, and how a full replacement runs from measure to install.
Three Ways to Double Glaze Existing Windows
There are three ways to add double glazing to a home without building new openings. Each method keeps a different amount of the old window, so each one delivers a different result. These are the three options a Perth homeowner can choose from.
Retrofitting a Double Glazed Unit Into the Existing Frame
Retrofitting means removing the single pane and fitting a sealed double glazed unit into the same frame. A sealed unit, also called an insulated glass unit (IGU), is two panes of glass held apart by a spacer around a sealed gap of air or argon gas. The frame, seals and locks stay as they are, so only the glass changes. Retrofit works only when the glazing rebate is deep and strong enough to carry the thicker, heavier unit. The rebate is the channel that holds the glass, and frames built for a single 3 mm or 4 mm pane often have little room to spare.
Adding Secondary Glazing Inside the Window
Secondary glazing leaves the original window untouched and fixes a second pane of glass or acrylic to the inside of the frame or reveal. The still air trapped between the old glass and the new panel slows heat flow and blocks sound. Many systems hold the panel with magnetic strips, so it can be lifted out for cleaning. Secondary glazing is the least invasive option, which makes it popular for rentals and heritage homes. It cannot add new locks, fix a draughty frame or match the seal of a factory-made unit.
Replacing the Whole Window With New Double Glazing
Full replacement removes the old window, frame and all, and installs a new window built for double glazing from the start. The new window arrives with an insulated frame, a factory-sealed argon-filled unit, new weather seals and multi-point locks. Replacement costs the most per opening and takes the longest to arrange because every window is made to measure. It is also the only option that upgrades the frame as well as the glass. For single glazed aluminium homes, which make up much of Perth’s older housing, replacement is the option Canon Double Glazing recommends most often.
All three methods improve on a bare single pane, but they do not improve it by the same amount. The gap between them comes down to one part of the window that most people never picture when they think about double glazing.
Why the Frame Decides How Well Double Glazing Works
The frame decides how much of the new glass’s benefit actually reaches your room. Heat takes the easiest path through a window, and in an old aluminium window that path is often the metal frame rather than the glass. Aluminium soaks up the sun outside and passes that heat straight to the inside face. Better glass in the same frame still leaves a metal bridge for heat to cross in summer and escape through in winter.
Figures from the Australian Government’s YourHome glazing guide show how much the frame matters. A U-value measures how easily heat passes through a whole window, and a lower number means better insulation. YourHome lists a single glazed aluminium window at a U-value of 6.9, and the same 3 mm/6 mm air/3 mm double glazed unit at 4.2 in aluminium but 3.0 in timber or uPVC. That is about 29% less heat flow from changing the frame alone. Engineering ToolBox data puts common aluminium alloys at 150 to 190 W/m·K against about 0.19 W/m·K for PVC, so aluminium conducts heat roughly 800 to 1,000 times more readily.
The glass you choose matters, but the frame sets the ceiling on what that glass can achieve. That is why the right upgrade depends so heavily on what your current frames are made of and what shape they are in.
Which Frames Suit Retrofit and Which Need Replacement
Retrofit suits sound, deep timber frames, while old single glazed aluminium almost always needs full replacement. The material sets how much heat the frame leaks, and its condition sets whether it can carry a heavier sealed unit at all. These are the frame types found in most Perth homes and what each one suits.
Single Glazed Aluminium Frames
Standard aluminium frames without a thermal break are the weakest candidates for retrofit. A thermal break is a strip of low-conducting material that separates the inside and outside of a metal frame, and most older Perth sliders do not have one. Their glazing channels are usually too shallow for a full-depth sealed unit, so any retrofit unit ends up with a narrow, less effective gap. Coastal salt adds a second problem. The Western Australian Department of Finance notes that corrosive conditions around Perth can extend several kilometres inland, which shortens the life of exposed metal.
Timber and Character-Home Frames
Timber insulates naturally, so a solid, deep timber frame can be a genuine retrofit candidate. That makes retrofit or secondary glazing attractive in character homes where the original look matters. Condition is the deciding factor. Rot, soft sills, sticking sashes and joints that move under light pressure all signal a frame near the end of its life. English Heritage testing found that secondary glazing lowered the U-value of a single glazed timber sash window from 4.8 to about 2.9, which shows how well sound timber responds to an added layer.
Heritage-Listed Homes, Rentals and Strata Properties
Some owners cannot change the window at all. A heritage listing may protect the original joinery, a lease may stop tenants altering the building, and strata by-laws may control what appears on the outside of each unit. In these cases secondary glazing is often the only practical option because it fits inside and can be removed later. Check with your local council, the Heritage Council of Western Australia or your strata company before ordering work, as approval rules differ between properties.
Knowing your frame type narrows the choice. The final call, though, depends on what you find when you look closely at each window in your own home.
How to Check if Your Existing Windows Can Be Double Glazed
You can assess most windows yourself in about 10 minutes per room. Work through the checklist below for each window and note every problem you find. One problem or none suggests the frame may accept a retrofit, while three or more problems usually point to replacement.
- Frame material. Note whether it is aluminium without a thermal break, timber or uPVC.
- Rot or corrosion. Look for soft timber, flaking paint or white powdery pitting on aluminium.
- Gaps and draughts. Check for daylight or moving air around the edges when the window is shut.
- Operation. Note sashes that stick, rattle in the wind or need force to lock.
- Sill condition. Look for water stains, swelling or soft spots on the sill.
- Winter condensation. Note water pooling on the frame or sill on cold mornings.
- Channel depth. Ask your installer whether the glazing channel can hold a full-depth sealed unit.
Draughts deserve extra attention because they undo much of what new glass can achieve. In testing reported by English Heritage, draughtproofing a window cut air leakage by over 50% and improved energy savings by over 25%. A retrofit keeps the original seals and gaps, so a leaky frame stays leaky after the new glass goes in. A simple tally of passing and failing windows also gives you a far clearer basis for comparing quotes.
How Much Does It Cost to Double Glaze Existing Windows in Perth?
Secondary glazing is usually the cheapest per window, retrofit sits in the middle and full replacement costs the most upfront. The difference reflects how much of the window each option renews. The table below compares what your money buys with each method.
| Option | Upfront cost | What gets upgraded | What stays old | Best suited to |
|---|---|---|---|---|
| Secondary glazing | Lowest | Adds an inner panel | Window, frame, seals, locks | Heritage homes, rentals, noise-first fixes |
| Retrofit sealed unit | Moderate | Glass only | Frame, seals, locks | Sound, deep timber frames |
| Full replacement | Highest | Frame, glass, seals, locks | Nothing | Single glazed aluminium, worn frames |
For whole-home uPVC replacement, Canon Double Glazing’s current installed guide prices are shown below. Prices depend on the number of openings, window styles and site access.
| Home size | Indicative installed price |
|---|---|
| 3×2 home | $18,000 to $20,000 |
| 4×2 home | $25,000 to $30,000 |
| 5×2 or two-storey home | $35,000 to $40,000 or more |
| Single uPVC sliding window | $3,500 to $5,500 |
The upfront price is only half the sum because the upgrade also changes what you spend on cooling and heating. YourHome works through 70 m² of aluminium-framed clear glass at a U-value of 6.2, which loses about 6,510 W of heat when it is 15°C colder outside. Halving that U-value with double glazing avoids roughly 3,000 W of loss, and efficient windows can cut the air conditioner size a home needs by around 30%. The double glazed windows cost guide breaks down what drives each quote. Those running savings show up in how a home feels, which is what most owners notice first.
What Changes After You Double Glaze Existing Windows
Double glazing changes three things you can feel, which are summer heat, outside noise and winter condensation. How much each one improves depends on whether the frame was upgraded along with the glass. These are the changes Perth homeowners notice most.
Summer Heat and Cooling Bills
Windows are where most unwanted heat enters a home. YourHome estimates that up to 87% of a home’s heat gain and up to 40% of its heating energy loss happen through windows. Perth makes this especially costly, averaging 26.4 days a year above 35°C between 1994 and 2022, according to the Australia Institute. Canon Double Glazing customers typically report 20% to 35% lower summer cooling costs after a full uPVC replacement. Results vary with orientation, shading and how the home is used.
Outside Noise
Secondary glazing can block noise well because the gap between the old pane and the new panel is often much wider than a sealed unit’s cavity. YourHome notes that secondary glazing gives good noise control even though its thermal performance falls short of a factory-made unit. Full replacement can match that result with laminated or asymmetric glass, where the two panes have different thicknesses so they do not vibrate at the same pitch. Canon Double Glazing’s soundproof windows use this approach for homes near main roads, rail lines and flight paths.
Condensation on Glass and Frames
Condensation forms when warm indoor air meets a surface cold enough to turn its moisture into water droplets. YourHome explains that efficient glazing keeps the inner glass closer to room temperature, which reduces condensation and mould. A glass-only upgrade has a catch. If the old aluminium frame stays, it becomes the coldest surface in the window, so water simply moves from the glass to the frame edges. No window removes moisture from the air, so ventilation still matters with every option.
These results depend on more than the product. The quality of the fitting work decides whether a new window stays sealed, dry and quiet for decades.
How Replacing Single Glazing With Double Glazing Works
Replacing single glazed windows with double glazing runs in four stages, from a free measure to the final clean-up. Canon Double Glazing manufactures and installs every window in-house, so one team handles each stage. The typical sequence looks like this.
- Free measure and quote. A consultant measures each opening, checks frame condition and recommends the right fix for each window.
- Custom manufacture. Every window is made to fit its opening, with a lead time of about 6 to 8 weeks from final measure.
- Installation. The team replaces about 3 to 4 windows a day and only removes windows that can be fitted and locked up the same day. A typical 4×2 home takes 4 to 5 working days.
- Staged upgrades if needed. If the budget does not cover the whole home at once, the work can be split into stages, starting with the rooms that overheat most.
Correct fitting matters as much as the window itself. The Australian Glass and Window Association installation guide names installation problems as the prime cause of leaks in window assemblies, with missing flashing and blocked weep holes (small drainage holes in the sill) among the usual faults. The same guide notes that windows built to AS 2047, the Australian Standard for windows, should carry a label or certificate showing their wind and water ratings. The double glazed windows replacement page explains how Canon Double Glazing handles each install. Homes near bushland, though, face an extra set of rules before any window work starts.
Bushfire Zones and Approvals in the Perth Hills
Homes in bushfire-prone areas need windows that meet the Bushfire Attack Level (BAL) for the site under Australian Standard AS 3959. BAL rates how much ember attack, radiant heat and flame a building could face, and it sets the minimum glass and frame specification. Parts of the Perth Hills and outer suburbs sit in these zones, so confirm your BAL before choosing any upgrade. A retrofit unit or secondary panel does not automatically make an old window compliant.
Bushfire research from CSIRO on windows and doors describes poorly built windows as a weak point in a home, because glass can crack from radiant heat, strong wind or direct flame. Its guidance links annealed glass in a non-combustible or durable timber frame with BAL-12.5, toughened glass in a non-combustible frame with BAL-29 and fire-rated glass with BAL-40. CSIRO also recommends metal mesh screens with gaps under 2 mm on opening windows to keep embers out.
Settling the BAL, heritage and strata questions early prevents a costly redesign after a quote is accepted. With those boxes ticked, the questions that remain tend to be practical ones about timing, budget and do-it-yourself options.
Frequently Asked Questions About Double Glazing Existing Windows
These are the questions Perth homeowners ask most often about upgrading the windows they already have.
Can I double glaze existing windows myself?
Do-it-yourself secondary glazing kits exist, using acrylic sheets and magnetic strips, and they can help a draughty room. Retrofitting a sealed unit or replacing a whole window is not a realistic home job. Sealed units are heavy and fragile, and glass must suit its location under AS 1288, the Australian Standard for glass in buildings. The wrong glass in a door or low window creates an injury risk, so professional installation is the safer choice.
Is retrofitting double glazing worth it?
Retrofit is worth it when the frame is sound timber with a deep enough rebate and you want to keep the original look. It is rarely worth it in old single glazed aluminium frames. The metal keeps conducting heat and the shallow channel limits the size of the sealed unit. In those homes the money usually works harder in a full replacement.
Is there a cheaper alternative to double glazing?
Secondary glazing is the main lower-cost alternative, and it performs well against noise. Draught sealing, heavy curtains with pelmets and external shading also reduce heat transfer for a fraction of the price. YourHome notes that some window films can halve a window’s solar heat gain coefficient (SHGC), which measures how much of the sun’s heat passes through the glass. These measures help, but none matches a sealed unit in an insulated frame.
Can you retrofit double glazing into aluminium frames?
It is possible in some aluminium frames, but the result is usually disappointing. Most older aluminium sliders have shallow glazing channels that only fit a thin, narrow-gap unit. The frame also keeps conducting heat whatever glass you add, and coastal salt keeps corroding it. Full replacement with an insulated uPVC frame gives a far larger improvement in most Perth homes.
Does double glazing stop condensation?
Double glazing reduces condensation on the glass by keeping the inner pane warmer, but it does not stop condensation entirely. If the old aluminium frame stays, droplets often move from the glass to the frame. Indoor moisture still needs an exit, so opening windows, extraction fans and good airflow remain important.
Can I mix retrofit and replacement in the same house?
Yes, many homes use a different fix for different windows. A heritage front window might get secondary glazing, sound timber bedroom windows a retrofit and tired aluminium sliders at the back a full replacement. An assessment that looks at each window separately helps you spend more where it matters and less where it does not.
How long does it take to double glaze a whole home?
Canon Double Glazing’s full uPVC replacement has a lead time of about 6 to 8 weeks from final measure, because every window is made to order. Installation is much quicker. The team fits about 3 to 4 windows a day, so a typical 4×2 home is finished in 4 to 5 working days.
What are the downsides of double glazed windows?
The main downside is the upfront cost, which is higher than single glazing or simple fixes like curtains. Replacement also brings some disruption while old windows come out. Double glazing cannot fix poor ventilation, and a cheaply made unit can fail at its seals and fog between the panes. Choosing a quality frame and an experienced installer reduces these risks.
Choosing How to Double Glaze Existing Windows in Your Perth Home
Double glazing existing windows comes down to three methods, and the frame decides which one pays off. You can add a removable panel to protect a heritage window, retrofit a sealed unit into sound timber or replace tired aluminium outright. Leaving single glazing in place means more summers of heat pouring through the glass and more winters of water on the frames. Perth already averages more than 26 days above 35°C a year, so every year of delay is another year of higher cooling bills.
Canon Double Glazing manufactures and installs uPVC double glazed windows and doors in-house across Perth, with interest-free finance on full-home packages and warranty on frames, hardware and sealed units. You can book a free measure and quote or call (08) 9249 9974 for a straight recommendation for each window in your home.
