Why Is There Condensation Between My Double-Glazing Panes?
For mist, fog or water droplets trapped between the panes of a sealed double-glazed unit that cannot be wiped from either surface.
What this usually means
Condensation trapped between double-glazing panes usually means the sealed glass unit has failed. Moisture has entered the cavity between the panes, so wiping the inside or outside glass will not remove it. The Centre for Sustainable Energy advises that a misted double-glazing pane indicates seal failure and that a specialist may be able to replace only the failed sealed unit rather than the entire window and frame.
What may be causing this
The perimeter seal of the sealed glass unit has failed
Clues: The mist sits between the panes and cannot be wiped from the room side or outside.
What to do: The long-term repair is usually replacement of the failed insulated glass unit. The existing frame can often remain if it is otherwise sound.
Moisture has entered and the spacer/desiccant can no longer keep the cavity dry
Clues: Misting becomes more obvious on cold mornings, may come and go at first, and can develop into persistent clouding or droplets.
What to do: Once the sealed cavity is contaminated with moisture, cleaning the visible glass surfaces will not resolve it. Have the sealed unit assessed for replacement.
Age, movement or edge deterioration has damaged the seal
Clues: The affected unit is older, exposed to weather, or only one pane among several windows has failed.
What to do: Check installation paperwork and guarantees before paying for replacement; the problem may be limited to a single sealed unit.
The moisture is actually surface condensation, not seal failure
Clues: The water wipes away from the room-facing or external glass surface.
What to do: Treat surface condensation as a humidity, ventilation or temperature issue instead. Do not replace a sealed unit solely because ordinary surface condensation is present.
How to check what is happening
The moisture may be inside the sealed unit rather than on the indoor surface.
Condensation between the panes is strongly indicated.
A failed sealed unit is much more likely than temporary surface condensation.
It may be possible to replace only that glass unit instead of the whole window.
Can you fix this yourself?
Diagnosing the location of the moisture is straightforward, but replacing a sealed double-glazed unit is specialist work. Do not drill the panes or dismantle the glazing. A window fitter or glazier can measure and replace the failed unit while retaining a sound frame.
- Clean dry cloth
- Phone camera
- Window installation or guarantee paperwork
What you can safely try
- 1
Confirm that the moisture is really between the panes
Clean and dry the accessible inside surface, then check the external surface from a safe position. If the fog remains trapped where neither surface can be wiped, the sealed cavity is affected.
- 2
Rule out ordinary indoor condensation
If the water wipes off the room-facing glass, investigate indoor humidity and ventilation instead. A failed sealed unit and ordinary condensation need different fixes.
- 3
Check the installation guarantee
Look for installer paperwork, guarantees or registration records before arranging paid work. A failed unit may still be covered depending on its age and the terms of the guarantee.
- 4
Ask whether only the sealed unit needs replacing
If the frame, hinges and surrounding window are sound, ask the glazing professional to quote for replacement of the failed glass unit rather than automatically replacing the complete window.
Call a window fitter if…
- The glass is cracked, loose or visibly damaged.
- The frame is rotten, distorted or structurally unsound.
- The affected glazing is at height or would require unsafe access.
- Repair would require drilling, cutting or dismantling the sealed glass unit.
Get the right professional.
This problem can have more than one cause. Start with the checks above: a window fitter is the usual first route, while a glazier may be more appropriate when the clues point that way.
Sources used for this guide
We prefer primary UK guidance, regulators and manufacturers for technical and safety-sensitive claims.
- Energy efficient glazing and high performance external doorsCentre for Sustainable Energy
- Why are my double glazed windows misting up inside and how to fix it?Axiom Eco Homes
Last reviewed: 31 August 2026. Home Manual updates review dates only when the substance of a guide is checked or changed.