Misted double glazing repair
The seal has failed. We replace the glass unit and keep your frame.
When double glazing mists up, condenses between the panes or grows a tidemark, the edge seal on the sealed unit has failed. Moist air is getting into the cavity and condensing there. Nothing can be done to dry it out — the unit is finished.
The good news is that the frame is almost always perfectly fine. This is a glass job, not a window job, and anyone quoting you a whole new window for a misted pane is selling rather than diagnosing.
How to be sure it is the unit
Condensation between the panes, that you cannot wipe off from either side, means a failed seal. Condensation on the room side is a ventilation and humidity problem, not a broken window — see our guide on condensation. Condensation on the outside face on a cold morning is normal and actually indicates good insulation.
What we need to measure
- Width and height of the glass only, not the frame
- The overall thickness of the unit — commonly 24mm or 28mm
- Whether it is clear, obscure, toughened or leaded
- Whether there is a coating, and which face it is on
If you are not sure, photograph the spacer bar edge and any stamp in the corner of the glass. Most units carry a mark showing the specification.
Why they fail
Age, mostly — a sealed unit lasts around 15 to 25 years. Failure is faster on south and west-facing elevations, where daily heating and cooling works the seal harder, and faster again where the frame drainage is blocked so the unit sits in standing water.
Worth upgrading while it is out
The frame is open anyway, so this is the cheapest moment to improve the glass. A low-E coating and argon fill costs little more than a plain replacement and measurably improves the U-value. If the room is noisy or overlooked, acoustic or obscure glass costs the same labour.
A photograph is worth ten minutes on the phone. Send one on WhatsApp and we will tell you what it is and what it costs.
Questions
Can misted glazing be dried out or repaired?
No. Drilling and 'defogging' does not restore the seal or the gas fill, and the misting returns. Replacing the unit is the only real fix.
Do I need a whole new window?
Almost never. The frame is a separate component and usually has years left. Replace the sealed unit and keep it.
Do I need building regulations for this?
No. Replacing a sealed unit in an existing frame is a repair, not a replacement window, so it is not notifiable.
How long does it take?
The unit has to be made to size, so allow a few days from measure to fit. The fitting itself is usually under an hour per window.
Can I supply the measurements myself?
Yes — that is a supply-only glass order and it is the cheapest route if you are confident glazing it back in.