With energy costs rising and still a concern for most households, having windows that actually perform matters more than ever. If you’ve started to suspect your double glazing isn’t quite right, this guide will walk you through what’s likely happening and what you can do about it.
What Causes Double Glazing to Fail Over Time
Double glazed windows work by trapping an insulating gas (usually argon) between two panes of glass within a sealed unit. That sealed gap is where all the thermal performance comes from and over time, though, the seal around the unit can weaken. Temperature changes cause it to expand and contract repeatedly, and eventually even a small breach is enough to let the gas escape.
Once that happens, ordinary air replaces the insulating layer and moisture follows. That’s when you start seeing condensation forming between the panes, the kind you can’t wipe away from either side, because it’s trapped inside the unit itself. It’s one of the clearest signs that the seal has gone.
Spotting the Signs Before It Gets Worse
The most obvious indicator is persistent misting or fogging between the panes. It tends to be more visible on cold mornings or during damp weather, and it doesn’t clear up the way surface condensation does. Beyond the visible signs though, you might notice rooms taking longer to warm up, cold spots near windows that used to feel fine or slightly more outside noise than you remember. These are all signs that the insulating performance of the unit has dropped.
Left too long and the trapped moisture can start to cause problems beyond the glass itself creating damp patches, mould around the frame and damage to surrounding materials that turns a straightforward repair into something more involved.
To Repair or Replace – Understanding Your Options
In our experience, there’s no single answer that suits every situation, but it’s worth understanding what each option actually delivers. Resealing alone won’t restore performance. Once the insulating gas has escaped, a new seal doesn’t bring it back and while it may improve the appearance temporarily, the thermal efficiency stays compromised.
A more thorough approach involves removing the moisture from between the panes along with a seal replacement. This can reduce the condensation issue and improve how the window looks, though it still won’t fully match the performance of an intact unit.
For most homeowners, replacing the sealed unit entirely is the most effective route as it restores the window to its original condition and addresses the root cause rather than managing the symptoms. In the long run, it tends to offer better value and avoids the need to revisit the same window again down the line.
Why Acting Early Makes a Difference
Blown double glazing doesn’t improve on its own and the longer it’s left, the further performance drops, and the greater the risk of moisture causing wider damage to frames and surrounding areas. Getting it sorted early keeps your home efficient, avoids escalating repair costs and means you’re not losing heat through windows that are no longer doing their job. Even one failed unit can have a noticeable effect on comfort and running costs.
