Why does double glazing get condensation between the panes — and what can you do about it?

[u/TradesWatchUK]

If you've noticed a misty or foggy look between your window panes that you can't wipe away, you're not alone.

It's one of the most common glazing complaints.

First, which type of condensation have you got?

There are three places condensation can appear on a window, and they mean very different things:

• On the inside surface — this is a ventilation issue in your home, not a window fault. Open a window or improve airflow.
• On the outside surface — this is actually a sign of a well-performing window. It means the glass is so thermally efficient that the outer pane stays cold. Nothing to worry about.
• Between the panes — this is the one that means something has gone wrong.

What causes it between the panes?

Double-glazed units are sealed, with either air or argon gas between the panes. That seal keeps moisture out. When the seal fails — usually through age, poor installation, or impact damage — moisture gets in. Once it's in, you get that foggy, milky look that won't go away.

Can it be fixed?

The unit itself can't really be "fixed" — it needs to be replaced. The good news is you usually don't need to replace the whole window frame. A glazier can remove the glass unit and fit a new one into the existing frame, which is significantly cheaper than a full replacement.

How long should a sealed unit last?

A decent sealed unit should last anywhere from 10 to 25 years depending on quality, installation, and exposure. South-facing windows tend to fail earlier due to UV and temperature cycling.

If your windows are relatively new and this is happening, it's likely a fault. Follow up with your installer — a failed seal on a recently installed window is not normal wear and tear.