How Long Does Double Glazing Last? Signs You Need New Units
31 May 2026 · 5 min read
Double glazing doesn't last forever — but you can often replace just the glass, not the whole window. Here's how long it lasts and what the warning signs are.
How long it typically lasts
Most double-glazed sealed units last a good number of years before the seal begins to break down, though the exact lifespan depends on the quality of the original units, their installation, and how exposed they are. South-facing windows that heat and cool repeatedly, and units sitting in poorly drained frames, tend to fail sooner.
The frames themselves often outlast the glass — which is good news, because it usually means you only need to replace the sealed unit, not the whole window.
The clearest sign of failure
The unmistakable sign of a failed unit is misting or condensation between the two panes that you cannot wipe away from either side. Once moist air gets inside the sealed unit, the insulating layer is compromised and the glass looks permanently foggy.
You may also notice draughts, a chillier room, or higher heating bills as older glazing loses its thermal performance.
Repair the glass, not the whole window
When only the sealed unit has failed, a glazier can replace the glass while keeping your existing frame — far cheaper and quicker than a full window replacement. It is often a single short visit per window.
Full replacement is only really needed when the frame itself is rotten, distorted, or beyond economical repair.
Worth upgrading at the same time
Replacing a failed unit is the ideal moment to upgrade to a modern A-rated, low-emissivity unit that keeps more heat in, or to toughened or laminated glass for added safety and security. The labour is the same; only the glass specification changes.
If your windows are misting or feeling cold, we are happy to assess them and quote both like-for-like and upgraded options.
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