Condensation on windows is one of the most misunderstood home problems. Homeowners often assume it means their windows have failed — but this isn't always the case. The type of condensation and where it appears tells you a great deal about what's actually wrong and what needs to be done.
Condensation on the Inside Surface of the Glass
Condensation on the room-facing surface of your window is not a sign of a failed window. It's a sign of high humidity inside the room. Warm, moist air contacts the cold glass surface and water vapour condenses. The remedy is ventilation and humidity control, not window replacement. Opening trickle vents, using extractor fans in kitchens and bathrooms, and improving room airflow will reduce or eliminate this type of condensation. If your windows don't have trickle vents, a UPVC specialist can drill and fit them.
Condensation Between the Panes
Condensation or misting between the two panes of double glazing is a definitive sign that the hermetic seal on the sealed unit has failed. Once moisture gets into the sealed unit, it cannot be removed by ventilation or heating. The only permanent solution is to replace the sealed unit. The frame can usually be retained — only the glass panel needs replacing. The Glass Guardian measures and fits replacement sealed units to all standard and non-standard sizes.
Condensation on the Outside Surface
This is actually a sign of a well-performing window. Modern A-rated double and triple glazing is so thermally efficient that the outer pane stays cool even when it's warmer outside. Dew forms on the cold outer surface in the morning — exactly as it does on car windscreens. This is normal and requires no action. If you find this puzzling or would like confirmation, a UPVC specialist can confirm your windows are performing correctly.
Running Water on Window Sills After Rain
Water on the inner sill that appears after heavy rain is a different problem entirely — this is water ingress, not condensation. Common causes include failed frame-to-wall silicone seals, cracked glazing gaskets, or blocked drainage holes in the frame. Each has a specific fix, and none requires window replacement. The Glass Guardian provides full diagnosis and repair for window water ingress across the West Midlands.
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