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Double glazing is an excellent investment in a home, so it’s fair to ask how long double glazed windows last before spending the money. The answer depends on which part fails, when and why, which is more nuanced than most guides suggest.
Quality double glazing, installed correctly in a typical Australian home, should last 20 to 30 years or more. This guide explains the factors that affect that range, the common signs of failure and what double glazing needs to reach its full life.
If you’re considering new double glazing and want to understand the product options before thinking about lifespan, our guides to double glazed casement windows and window replacement in Melbourne are useful starting points — the first covers how casement windows are specified and what to look for in a quality product, and the second walks through the replacement process and what to expect from an installer.
A double glazed window is a system with several components, and they don’t all age at the same rate. The frame, the sealed insulating glass unit (IGU), and the hardware each have their own lifespan, and failure in any one of them constitutes a problem even if the rest is fine.
The insulating glass unit — the sealed double glazed panel itself — is typically the element people are most concerned about. The IGU consists of two panes of glass separated by a spacer bar and a sealed air gap. The hermetic perimeter seal, formed during the manufacturing process, keeps the cavity dry and (where argon gas fill is used) keeps the gas in. When the seal fails, allowing moisture into the cavity, the desiccant in the spacer becomes saturated, and fogging or condensation appears between the panes. This is the classic failure mode of double glazing.
Under good conditions, quality IGUs should maintain their seal for twenty years or more. Some last considerably longer.
The factors that shorten seal life include:
The frame typically outlasts the glass unit. Quality uPVC frames are low maintenance and, when formulated for Australian UV, typically last 25 to 40 years. Powder-coated aluminium frames in normal suburban conditions can last forty or fifty years without structural failure. Timber windows can last a long time too, but wooden windows need regular painting and sealing to get there. In coastal environments with salt air, the frame finish and hardware are under more stress and deteriorate faster without an appropriate marine-grade specification.
Hardware — hinges, winders, handles, locks, rollers, and seals — is the component category that typically requires the most maintenance attention over the window’s life. These are wear parts that see daily use, and their lifespans range from 5 to 20+ years, depending on quality, usage frequency, and environmental conditions.
When thinking about lifespan, it’s also useful to consider how long it takes for the initial investment to pay itself back through energy savings and comfort improvements. This guide to the double glazing payback period outlines what homeowners can realistically expect based on different climates, usage patterns, and window specifications.
Four variables have the greatest influence on how quickly double glazing degrades. Understanding them helps set realistic expectations and supports better specification and maintenance decisions.
In Australia’s climate, the thermal demands on double glazed windows are substantial. A window frame and glass unit in an Australian home can cycle through significant temperature ranges daily — cool nights and hot days, particularly in inland regions with continental temperature swings and extreme weather. Each cycle of heat and cooling causes the glass, spacer, and sealant to expand and contract at slightly different rates. Over thousands of cycles across decades, this stress accumulates and can eventually compromise the seal.
West- and north-facing windows are under greater thermal stress than east- and south-facing ones, particularly in summer. Ultraviolet (UV) degradation of the silicone or polysulfide edge seal also occurs faster on sun-exposed elevations. This is one reason IGU failure is often noticed first in windows facing the afternoon sun, and why orientation and exposure matter for how long a seal holds up.
This is the factor that most homeowners have no way to assess from a completed installation, yet it has an enormous influence on how long the IGU lasts.
A double glazed unit that is installed with inadequate ventilation in the frame rebate — where condensation accumulates against the IGU edge — will have its seal attacked by sustained moisture exposure. A unit that’s been handled and installed without adequate edge protection, or that sits on hard packers without appropriate clearance, can develop problems that manifest years later. The installation quality substantially affects lifespan, and it’s one of the strongest arguments for using experienced, reputable installers rather than the cheapest option.
In Australia, the environmental variables that most significantly affect the lifespan of double glazing are UV intensity, thermal extremes, and salt air.
Coastal environments are the most demanding. Salt-laden air accelerates corrosion in aluminium frames that aren’t appropriately specified, attacks hardware, and can degrade certain sealant formulations faster than in sheltered suburban locations. Windows within a kilometre or two of the coast — and particularly those facing the sea — should be specified with marine-grade hardware and finishes, and may require more regular maintenance attention to achieve the same lifespan as equivalent windows in an inland suburban context. Good sealing between the frame and the wall also prevents water ingress, which protects both the window and the structure around it.
High-UV environments accelerate the degradation of edge sealants and frame finishes generally. Most of Australia falls into this category to varying degrees; southern Victoria and Tasmania experience less intense UV than Queensland or inland Western Australia.
The quality differential between manufacturer grades of double glazed IGUs is real and has a direct bearing on lifespan. A budget IGU using a poor-quality spacer, inadequate sealant depth, insufficient desiccant, and thin edge-seal construction will fail sooner than a quality unit. The difference isn’t always visible in the product before it’s installed, which is why product specification and manufacturer credentials matter in procurement decisions.
Warm-edge spacers — made from materials with lower thermal conductivity than the aluminium spacers used in traditional double glazing — reduce thermal stress on the edge seal, typically extend seal lifespan, and improve thermal performance at the glass edge. They’re worth specifying in any quality double glazed installation.
The most visible and sure sign of IGU failure is fogging between the panes — a haze, condensation streaks, or deposits that appear in the cavity and can’t be wiped off because they’re inside the sealed unit. This is the result of seal failure, allowing atmospheric moisture in.
Failed seals don’t recover. Once the seal is compromised and moisture has entered the cavity, the energy efficiency of the unit drops, its insulation value moves toward that of single glazing as the gas fill escapes, and noise reduction suffers too. You may notice higher heating bills and energy bills, or feel draughts of cold air near the window where it used to feel comfortable.
Other common signs of aging that don’t necessarily indicate IGU failure include:
A failed IGU cannot be repaired — the seal cannot be meaningfully restored once it has broken down and moisture has entered. The glass unit needs to be replaced.
The good news is that in most cases, the IGU can be replaced within the existing frame without replacing the whole window. If the frame is in good condition — structurally sound, weather seals intact, hardware functional — the glazier removes the failed unit and installs a new one. This is typically a far more cost effective way to restore performance than replacing the whole window, and it’s the appropriate response when the frame has years of service life remaining.
Full window replacement makes more sense when the frame itself is deteriorated, when the existing products are so aged that replacement hardware and seals are difficult to source, or when a performance or aesthetic upgrade is being pursued simultaneously.
A modest amount of proper care makes a meaningful difference to how long both the frame and the IGU perform, on windows and doors alike. These are the steps most worth building into a regular maintenance routine:
Well maintained windows routinely reach the upper end of their expected lifespan.
Most manufacturers offer fixed-term warranties on double glazed IGUs, typically ten to fifteen years against seal failure and fogging. Premium products sometimes carry longer warranties. Frame warranties vary by manufacturer and material. Be wary of a “lifetime guarantee” that doesn’t spell out what’s covered and for how long; a clear fixed-term warranty is usually worth more. APS backs its windows and doors with a 10 year warranty.
Warranty is worth reading carefully before purchasing. Key things to check: what exactly the warranty covers (the IGU itself, or installation too?), what conditions apply (some warranties are voided by painting over frames, modifying the window, or installation by non-approved trades), and who the warranty obligation sits with (the manufacturer, the distributor, or the installer).
Well-specified, properly installed double glazing in a quality frame should last twenty to thirty years in most Australian conditions, with the frame likely outlasting the glass units. The main risk is seal failure, driven by product quality, installation, UV and heat exposure, and maintenance.
When a seal does fail, replacing the glass unit in a sound frame is usually the right call. Choose quality products, have them installed properly, keep hardware and drainage maintained, and your windows will stay energy efficient for their full expected life.
APS Double Glazing supplies and installs uPVC double glazed windows and doors across Melbourne, backed by a 10 year warranty. For more articles on caring for and choosing double glazing, visit our guides.
Quality double glazing installed in typical Australian conditions should last twenty to thirty years or more. The insulating glass unit (IGU) is usually the first element to reach the end of its service life due to seal failure; the frame, whether uPVC or aluminium, typically has a longer serviceable life.
The most common failure mode is a breakdown of the hermetic seal around the IGU, allowing atmospheric moisture to enter the cavity. This is caused by a combination of thermal cycling, UV degradation of the edge sealant, product quality, and installation standards. Coastal salt air and high UV environments accelerate the process.
Once the IGU seal has failed and the unit is fogging, the glass unit cannot be repaired — it needs to be replaced. In most cases, the IGU can be replaced within the existing frame without replacing the whole window, which is typically the appropriate and more cost-effective response.
Fogging, condensation, or mineral deposits visible between the panes — which can’t be wiped off because they’re inside the sealed unit — indicate seal failure. This is the clearest sign. Condensation on the inner glass surface is a different issue (usually room humidity) and doesn’t necessarily indicate seal failure.
Yes. Coastal environments with salt air, high-UV regions, and locations with extreme daily temperature cycling are more demanding on double glazed units. Windows in sheltered suburban environments in temperate climates typically achieve longer seal life than windows in coastal, high-UV, or thermally extreme conditions.
The most effective steps are:
Good maintenance can meaningfully extend the effective life of both the frame and the IGU.
If the frame is in good structural condition with serviceable hardware and seals, replacing only the IGU is usually the right choice and is significantly less expensive than full window replacement. Full replacement makes more sense when the frame is also deteriorated, when the products are very old, or when a performance or design upgrade is being undertaken at the same time.