Quick answer: The frame of a quality double glazed window lasts 20–35 years, but the sealed glass unit inside it (where the insulation actually happens) usually fails after 10–25 years. So the question “how long do my windows last” really has two answers — and the second number matters more, because that’s the one that decides whether you’re losing heat through your walls.
This guide cuts through the warranty marketing and explains what actually wears out first, what kills windows early, and when to repair vs replace. Honest, no pressure. Written for UK homeowners in 2026.
The honest answer — what actually fails first
A “double glazed window” is really three things bolted together: the frame (uPVC, aluminium, timber, or composite), the sealed glass unit (two panes of glass with a gas-filled gap), and the hardware (hinges, locks, handles, gaskets).
Each part has a different lifespan, and they don’t fail at the same time:
- Sealed glass units fail first — typically 10–25 years. When the perimeter seal goes, moisture gets in, you see misting between the panes, and your insulation drops sharply.
- Hardware fails second — hinges, locks and handles wear out at 15–20 years. Easy and cheap to replace.
- Gaskets and seals (the rubber strips around the frame) crack and shrink at 15–25 years. Replaceable.
- Frames last longest — 20–35 years for uPVC, 30–45 for aluminium, 50+ for properly maintained timber, and 35+ for composite.
This means the most common failure isn’t “the window’s gone” — it’s “the glass unit has misted up but the frame’s fine.” That’s a different (and usually cheaper) repair. We cover that in our misted window repair guide.
Lifespan by material type
| Frame material | Typical lifespan | Best for | Watch out for |
|---|---|---|---|
| uPVC | 20–35 years | Most UK homes; best £/year value | Cheap brands discolour and warp from year 10 |
| Aluminium | 30–45 years | Modern homes, large openings | Cold bridging if the thermal break is poor |
| Timber (hardwood) | 50+ years with maintenance | Period properties, conservation areas | Needs repaint/restain every 5–8 years or rot starts |
| Composite | 35+ years | Doors more than windows | Very few UK installers — premium price |
The numbers above are for a quality install in a typical UK climate. Coastal homes (salt air), south-facing walls (UV) and poorly installed windows can cut these by 30%.
7 signs it’s time to replace your windows
- Misting or condensation between the panes. The seal has failed — your “double” glazing is now effectively single. More on misted units →
- Draughts you can feel with your hand near the frame edge — gaskets have shrunk or the frame has warped.
- Frames that are difficult to open or close — frame distortion or hinge wear.
- Visible damage — cracks, holes, rotten timber, discolouration that bleach won’t shift.
- Heating bills creeping up for the same usage pattern (compare year-on-year on the same tariff).
- Cold spots when you put your hand on the glass — even brand-new triple glazing feels cold to the touch in winter, but it shouldn’t be ice-cold near the edges.
- External noise getting louder — the acoustic seal is part of the same gasket system. When seals go, sound comes in.
One or two of these mean a repair (gaskets, hinges, or a single sealed unit). Three or more, especially across multiple windows, usually means it’s time to budget for full replacement.
What kills windows early (5 things to avoid)
- Cheap installation. A £200 cheaper quote often means thinner gaskets, no warm-edge spacers, or a rushed seal that fails in 8 years instead of 18. The biggest single factor in window lifespan is the quality of the original install — not the brand on the frame.
- Pressure-washing the frames. High-pressure water forces water past gaskets and accelerates seal failure. Use a soft cloth and warm soapy water.
- Painting uPVC or aluminium with the wrong paint. Standard gloss flakes within a year and traps moisture against the frame.
- Ignoring small leaks. Water sitting on a sealed unit for months will eventually wick into the seal.
- Letting timber go unpainted. 4–5 years is the absolute maximum between coats; longer than that and you’re looking at sash repairs, not just touch-ups.
How to extend the life of your double glazing
- Clean gaskets twice a year with a soft cloth and a tiny amount of silicone spray on the rubber. Stops them drying out.
- Lubricate hinges and locks annually (any dry PTFE or silicone spray — never WD-40 long-term, it attracts dust).
- Open windows regularly in winter to clear internal condensation off the inside surface — moisture accelerates frame degradation around the bottom edge.
- Repaint timber on a 5-year cycle minimum. Sand back, prime, two coats of micro-porous paint.
- Check the drainage holes at the bottom of uPVC frames once a year — they clog with debris and standing water rots the bottom seal.
Repair vs replace — which is right?
A simple rule: if the frame is sound but the glass unit has failed, repair. If multiple windows are failing at once, replace.
- Repair the glass unit only (£40–£80 per pane) when: 1–2 windows have misted, the frames look fine, and the windows are under 18 years old.
- Replace whole windows (£300–£700 per window) when: 3+ are misting, the frames are cracked/discoloured, draughts are widespread, or the windows are over 25 years old.
- Replace just the hardware (£15–£60 per item) when: only the locks, hinges or handles have failed.
For a precise estimate based on your home’s size and city, try our double glazing cost calculator — it gives a budget range in 30 seconds, no contact details required.
Frequently asked questions
Do double glazed windows really last 20 years?
The frames usually do. The sealed glass units inside them often don’t — typical real-world failure is 10–25 years for the glass, even when the manufacturer’s marketing claims “lifetime.” Always read the warranty’s small print: most cover the frame for 10 years and the glass unit for 5 years.
Will Anglian / Safestyle / Everest windows last longer than budget brands?
The frames are similar quality across most major UK brands — they all source from a small number of UK extruders. The bigger lifespan factor is the quality of the install. A £4,500 set of windows fitted by a careless team can fail in 12 years; a £5,500 set fitted properly can last 25+. Read how to vet a fitter →
Is a 30-year-old window worth replacing?
Almost always yes. A 30-year-old sealed unit is performing closer to single glazing than to modern A-rated double glazing. Energy savings alone usually pay back the cost within 8–12 years for a typical 3-bed semi.
Does the warranty actually mean anything?
Only if the company is still trading. Several major UK brands (Safestyle, Everest) have entered administration in the last 24 months. The protection that survives is the insurance-backed guarantee (IBG) — usually via Installsure or QANW — which covers you if the original installer goes bust. Always confirm IBG before signing.
Triple glazing — does it last longer than double?
Slightly. The extra pane shields the seal from one direction of UV. Real-world difference: maybe 2–5 years extra on the sealed unit. Not enough on its own to justify the 20–30% price premium — but worth it for sound and thermal performance reasons.
Get installer quotes for replacement
If your windows are showing the warning signs above, our quote service connects you with up to 4 FENSA-registered local installers within 24 hours. Free, no obligation, no high-pressure sales pitch (or we drop the installer from our network).
Sources used in this guide: BWF (British Woodworking Federation) lifespan data, Pilkington WER ratings, FENSA installer guidance, Hazlemere Windows lifespan analysis (2025), Anglian Home Improvements warranty terms (2026), Installsure IBG terms (2026). Last reviewed: April 2026.
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