Double glazing lasts longer than most people expect, but the frame and the glass age separately, and almost every disappointment comes from confusing the two. A uPVC frame lasts 20 to 25 years, aluminium 30 to 40 years and well-maintained timber 30 to 60 years. The sealed glass unit, though, typically lasts 15 to 20 years before any misting, and most installers back the work with a 10-year guarantee. So the honest answer to how long double glazing lasts is that you will probably replace glass once during the life of the frames. If you are weighing whether new windows are worth the spend over that lifetime, see our guide on whether double glazing is worth it.
Lifespan by frame material
The frame material sets the headline lifespan. uPVC is the value choice and lasts a solid 20 to 25 years with no maintenance. Aluminium lasts longer at 30 to 40 years and resists weathering well. Timber can outlast them all, 30 to 60 years, but only if you repaint it every 8 to 10 years; neglect it and it rots. The table below pairs each material with its lifespan and upkeep.
| Material | Lifespan | Maintenance | Best for |
|---|---|---|---|
| uPVC | 20-25 yrs | None | Most modern UK homes; best value |
| Aluminium | 30-40 yrs | None | Slim modern frames, large openings |
| Timber | 30-60 yrs | Repaint every 8-10 yrs | Period and conservation-area homes |
Source: DGCC 2026 dataset, widely cited lifespan figures.
Those ranges assume a competent installation. A frame is only as durable as the fit: a uPVC window packed badly, out of square, or with the drainage slots blocked will age at the bottom of its range rather than the top, whatever the profile is made of. It is one of the reasons the installation process matters more to long-term cost than the brand name on the frame.
People obsess over the frame, but it is the sealed unit that goes first. I have pulled out twenty-year-old uPVC frames that were perfectly sound, just with misted glass. Swap the unit, keep the frame, save a fortune.
Tom Bradley, window installer
How long before double glazing mists up?
The two panes of glass are bonded around the edge into a sealed unit, separated by a spacer bar packed with desiccant and filled with an inert gas. A peer-reviewed review of insulating glass unit durability published in Buildings puts it plainly: degradation of these units is most often associated with edge seal failure, inter-pane gas loss, and breakdown of the low-emissivity coating. Those three failures are what you are actually buying against when you pay for a better unit.
Only one of them is visible. When the edge seal finally lets go, moisture enters the cavity, saturates the desiccant, and you get misting or condensation between the panes that you cannot wipe away. That typically happens at 15 to 20 years, sooner than the frame wears out. It is the single most common reason a double-glazed window looks tired while the frame is still fine, and our condensation guide explains how to tell it apart from the two harmless kinds of condensation.
Gas loss, by contrast, is invisible and starts on day one. The European standard for insulating glass units, BS EN 1279-3:2018, does not require a perfect seal. It permits an average gas leakage rate of no more than 1.0% per year, with no individual unit exceeding 1.20%, and requires the measured concentration after long-term testing to sit within 5 percentage points of the manufacturer's declared figure. A unit sold as 90% argon must still test at 85% or better. The practical consequence is that a fifteen-year-old window is slightly worse at its job than the day it was fitted, well before anything looks wrong, which is why the U-value on your paperwork describes a new window rather than an old one. Our argon versus krypton comparison covers what the fill is doing in the first place.
How exposure and orientation change the answer
Two identical windows in the same house rarely fail at the same time. The edge seal is a polymer, and polymers age faster under heat, ultraviolet light and repeated movement. Research on unit degradation uses exactly those stresses (thermal cycling and ultraviolet exposure) to age seals artificially in the lab, because they are what does the damage in the field. That maps directly onto which windows in your house go first.
| Factor | Why it shortens sealed unit life | What helps |
|---|---|---|
| South and west elevations | Highest glass temperatures and the most ultraviolet reaching the secondary seal, so more thermal cycling and faster polymer ageing | Better quality edge seals; expect these units to fail first |
| Standing water in the frame | A seal kept permanently damp fails far sooner than one that dries out | Keep drainage slots clear; this is basic aftercare |
| Coastal and highly exposed sites | Salt and wind-driven rain attack hardware, gaskets and finishes rather than the glass | Marine-grade hardware, more frequent cleaning and lubrication |
| Large or heavy units | More glass deflection puts more shear stress on the edge seal | Correct packing and setting blocks at installation |
| North-facing and sheltered | Least heat, least ultraviolet, least movement | Nothing; these are the units that reach the top of the range |
Mechanisms per published insulating glass unit durability research; site factors reflect standard UK glazing practice. Not a prediction for any individual window.
If a customer tells me one window has gone and the rest are fine, my first question is which side of the house it is on. Nine times out of ten it is the sunny side, or it is the one where the drainage slots are packed with moss and the bottom of the unit has been sitting in water for years.
Tom Bradley, window installer
What the guarantee covers versus what actually fails
The Glass and Glazing Federation states the industry norm as a 10-year guarantee on windows and doors, usually covering the glass, frame and ironmongery. That is the benchmark to hold a quote against. The trap is that the headline number and the small print often disagree. Some installers publish a shorter period for the sealed units than for the frames, so a quote advertised as a 10-year guarantee can turn out to give the glass five. Since the glass is the component most likely to fail inside that window, that split matters far more than it sounds. Ask for the guarantee document before you sign, not after.
Insist that the guarantee is insurance-backed. An insurance-backed guarantee is a cease-to-trade policy: it steps in if the firm that installed your windows goes out of business and can no longer honour the promise it made you. It is paid for in full by the installer on your behalf, and the competent person schemes require their registered installers to provide one, which is a practical reason to use a scheme-registered fitter over a cheaper unregistered one. Our FENSA guide covers the certificate side of the same decision.
Behind any guarantee sit your statutory rights, which are separate and cannot be signed away. Under the Consumer Rights Act 2015 you have six years in England, Wales and Northern Ireland, and five years in Scotland, to pursue a remedy for breach of those rights. That is a deadline for bringing a claim rather than a promise the product will last that long, but it is genuinely useful: a sealed unit that fogs at year four is not normal wear, and the claim is worth making even if a five-year glass guarantee has just expired. The rules around glazing also shift on a far shorter cycle than the windows do, from the Part L replacement standard tightening in 2023 to the EPC C deadline landlords face in 2030, which is why we keep a running record of double glazing news and policy updates. Check the double glazing news and policy updates before you plan a replacement, because grant eligibility in particular changes from one year to the next.
| Component | Typical service life | What usually goes wrong |
|---|---|---|
| Handles, hinges, locks | First thing to need attention | Stiffness, drop, wear; almost always replaceable as parts |
| Gaskets and weather seals | Before the glass | Hardening and shrinking, causing draughts and whistling |
| Sealed glass unit | 15 to 20 years | Edge seal failure, gas loss, misting between the panes |
| uPVC frame | 20 to 25 years | Discolouration, distortion, welds opening at corners |
| Aluminium frame | 30 to 40 years | Finish degradation, thermal break issues, corrosion on coastal sites |
| Timber frame | 30 to 60 years | Rot where the finish has failed, usually at the bottom rail |
Frame and unit lifespans from the DGCC 2026 dataset; failure modes reflect standard UK glazing practice.
Misting and repair: when a swap beats a replacement
Misting is a repair job, not always a replacement job. If the frame is sound, an installer can often replace just the sealed glass unit, which costs far less than a whole new window. Hinges, handles and seals are likewise replaceable, and a warm edge spacer in the replacement unit will usually outperform the aluminium spacer that came out of it. Always price the repair before agreeing to a full house, because a fitter who insists on replacing sound frames over one misted pane is not acting in your interest, as our guide to avoiding overcharging explains. The repair cost calculator will give you a figure before you make the call.
Use these rules of thumb to decide which side of the line you are on.
- Repair when the frame is square, the hardware works or can be re-parted, and one or two units have misted. Swapping glass into a sound frame is the cheapest good outcome available to you.
- Repairwhen the windows are under 15 years old. You are well inside the frame's life, and a new unit should see out the rest of it.
- Replace when the frame has failed rather than the glass: rot in timber, distortion or open corner welds in uPVC, seized hardware you cannot get parts for.
- Replace when frames are past 20 years and several units have gone. At that point you are paying twice, and a rolling repair bill in ageing frames is the worst value of the three options.
- Consider replacing anyway if the existing glazing predates modern coatings. A single-glazed or early sealed unit will be so far off current energy ratings that the comfort gain justifies the spend on its own.
A failed seal on one window is not a reason to redo the whole house. Anyone telling you otherwise is selling, not advising. Replace the unit that has gone and leave the sound ones alone.
Tom Bradley, window installer
Getting the longest life from your windows
Choose the material that suits both your home and your willingness to keep up the aftercare: uPVC if you want fit-and-forget, timber only if you will keep up the repainting. Beyond the material choice, a small amount of routine work has a disproportionate effect on how long the sealed units survive, because most of it comes down to keeping the edge seal dry.
- Keep the drainage slots clear. The small slots along the bottom of the outer frame let rainwater out. Blocked with moss or dirt, the bottom edge of the sealed unit sits in standing water, and that is the fastest way to kill a seal early.
- Lubricate hinges and locks annually. Hardware is the first component to need attention and the cheapest to keep alive. A dropped sash also strains the unit it carries.
- Check the gaskets. Hardened or shrunken seals let in draughts and water. They are a cheap replaceable part, not a reason for a new window.
- Repaint timber on schedule.Every 8 to 10 years, and sooner on an exposed elevation. Timber's long life is entirely conditional on this.
- Ventilate. Persistent internal condensation running down onto the frame and sill damages timber and encourages mould. Trickle vents exist for exactly this.
- Keep the paperwork. The guarantee, the insurance-backed guarantee certificate and the compliance certificate all matter when something fails early or when you sell.
For a heritage home that justifies the longer timber life, the timber window calculator prices the job, while the worth-it guide weighs the spend against the years of comfort you get back.
Frequently asked questions
Quality double glazing lasts around 20 to 25 years for uPVC frames, 30 to 40 years for aluminium, and 30 to 60 years for well-maintained timber. The sealed glass unit itself typically lasts 15 to 20 years before any misting. Most reputable installers offer a 10-year guarantee.
Misting appears when the edge seal around the sealed unit fails and lets moisture into the cavity. On a decently made unit that usually happens somewhere between 15 and 20 years. It can happen much sooner if the unit sits in a frame that lets water pool around the edge seal, or on a heavily sun-exposed elevation where the secondary seal takes more ultraviolet and thermal stress.
The frame and the sealed glass unit age at different rates. The seal around the glass unit eventually breaks down, letting moisture into the gap between panes, which shows as misting. That usually happens at 15 to 20 years, well before a uPVC frame reaches the end of its 20 to 25 year life.
Yes, slowly, and the standard allows for it. BS EN 1279-3:2018 permits an average gas leakage rate of no more than 1.0% per year, with no individual unit above 1.20%, and requires the gas concentration after testing to be within 5 percentage points of the manufacturer's declared figure. A well-made unit therefore loses a little insulating performance each year long before it visibly mists.
Misting or condensation between the two panes means the sealed unit has failed and lost its gas fill. The good news is you can often replace just the glass unit rather than the whole window, which is much cheaper.
Often yes. A misted or failed sealed unit can frequently be swapped out while keeping the existing frame, and worn hinges, handles and seals are all replaceable. Repair is usually far cheaper than a full window and worth pricing first if the frame is sound.
The industry norm is 10 years on windows and doors, and the Glass and Glazing Federation says that usually covers the glass, frame and ironmongery. Read the contract though: some installers publish a shorter period for sealed units than for frames. Insist the guarantee is insurance-backed so it stands even if the firm stops trading.
An insurance-backed guarantee is a cease-to-trade policy. It steps in if your installer goes out of business and can no longer honour the written guarantee it gave you. It is paid for in full by the installer on your behalf, and competent person schemes such as FENSA, CERTASS and ASSURE require their registered installers to provide one. It does not extend the guarantee period or cover anything the original guarantee excluded.
Separately from any guarantee, the Consumer Rights Act 2015 gives you six years in England, Wales and Northern Ireland to pursue a remedy for breach of your statutory rights, and five years in Scotland. That is a limitation period for bringing a claim, not a promise the goods will last that long, but it means an early sealed unit failure at year four is worth pressing even if the written guarantee has run out.
It can, at 30 to 60 years, but only with upkeep. Timber needs repainting every 8 to 10 years to protect the frame. Left unmaintained it rots and fails faster than uPVC, so its long life is conditional on the work you put in.
Replace when the frame itself has gone: rotten timber, corroded or seized hardware you cannot source parts for, distorted uPVC, or a frame that no longer holds a seal. Repair when the frame is sound and only the glass or the hardware has failed. If frames are already past 20 years and more than a couple of units have misted, replacement usually makes better sense than a rolling repair bill.