On a cold morning it is common to find water running down the inside of the windows. It is worth knowing where condensation is, because condensation in different places means very different things.

  • On the room side of the glass, it is usually caused by moisture in the air indoors.
  • Between the panes, it means the seal of the unit has failed. Cleaning will not help, and the unit needs replacing. See why double glazing mists up between the panes.
  • On the outside of the glass, it is normally harmless. On modern glazing it can even be a sign that the glass is keeping the heat in.

This article is about the first kind.

Why it happens

Warm air holds more moisture than cold air. When warm, damp air from inside the house meets a cold surface, it cools down and the moisture turns back into water. Windows are often the coldest surface in a room, so that is where it shows first.

Everyday life puts a surprising amount of moisture into the air. Cooking, showers and baths, drying clothes indoors and even breathing all add to it. Bedrooms often get the worst of it overnight.

How to reduce it

  • Open the trickle vents at the top of the frames, if you have them, and leave them open.
  • Use extractor fans when cooking or showering, and keep them running for a while afterwards.
  • Put lids on pans, and shut the kitchen or bathroom door while they are in use.
  • Dry clothes outside or in a vented dryer where you can.
  • Open a window for a few minutes each day, especially in bedrooms first thing in the morning.
  • Keep the heating steady, as cold rooms get more condensation than evenly warm ones.
  • Try a dehumidifier in rooms where the problem persists.

Wipe away any water that does form, as damp sills and frames can lead to mould.

Can different glass help?

It can make a difference. Modern units with energy efficient Low E glass keep the inner pane warmer than older double glazing, so condensation forms less readily on the room side. Units with warm-edge spacer bars also reduce the cold strip that often appears around the edges of the glass.

New glass will not fix a house that is generally too damp, though. Ventilation still matters.

If your condensation turns out to be between the panes, we can make a replacement unit to fit your existing frame. Read about misted window replacement, or contact us for a free quote.