Double glazing lasts longer than most people expect, but the frame and the glass age separately. 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. 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.
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, FENSA-registered installer
The sealed unit: why it fails first
The two panes of glass are bonded around the edge into a sealed unit with a gas fill between them. Over time that edge seal breaks down, moisture creeps into the gap, and you see misting or condensation between the panes that you cannot wipe away. This 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.
Misting and repair
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. 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.
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, FENSA-registered installer
Guarantees and what they cover
Most reputable installers offer a 10-year guarantee, and the best are insurance-backed so they stand even if the firm stops trading. The guarantee covers faults in the product and the fitting; it is separate from the FENSA certificate that proves the work meets Building Regulations. Keep both documents safe, because you will want them if a unit fails early and when you sell.
Getting the longest life from your windows
Choose the material that suits both your home and your willingness to maintain it: uPVC if you want fit-and-forget, timber only if you will keep up the repainting. 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.
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.
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.
Most reputable installers offer a 10-year guarantee, ideally insurance-backed so it stands even if the firm stops trading. The guarantee covers faults; it is separate from the FENSA certificate that proves Building Regulations compliance.
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.