Why condensation forms on windows and doors

Knowing why the condensation forms on glazing can help solve the problem quickly without too much expense. Each area of condensation is caused by something different:

Inner condensation is caused by an overabundance of water vapour in the air inside a home. When the outside of the window gets cold, the warm, damp air hitting the window on the inside will turn into condensation. Householders are likely to notice this happening more when they are cooking or showering, as well as during the autumn and winter, when the inside of a house is warmer than outside.

This type of condensation is very common on single-glazed panels and can easily form on more efficient double-glazed windows and doors too. People are surprised at the amount of water vapour that a household generates in a 24-hour period. Showering, drying clothes and cooking are all obvious sources of inner condensation, but people also create water vapour by simply breathing and going about their day.

Approximately 15.7 litres of water vapour are produced a day by the average four-person household. Without the proper ventilation, this can cause condensation and damp problems.

Outer condensation is caused by the same reaction, just the other way around. It affects properties which have very efficient windows and doors, and is caused by warmer air hitting the outside of a window. This is most likely to happen in the morning, as the sun is coming up and could happen in any season, depending on the conditions. This does not mean that the inside of the home is cold in comparison— it simply means that the glazing is so efficient that the outer pane is much colder than the inner one, hence the condensing reaction with the air outside.

Gap condensation happens because of the double-glazed unit failing. All double-glazed windows and doors have a small gap between the two panes. This space is filled with a harmless gas, which creates an insulating layer of air, thus helping to keep the warm air in and the cold air out. If the seal has broken around the edges of the unit, the insulating gas will escape and condensation will occur between the panes. This can, in some very extreme cases, cause the inner space to fill with water.

Related issues

Both inside and gap condensation cause problems and should be addressed as soon as possible to prevent further issues and expense.

Gap condensation within double-glazed units seriously reduces the energy efficiency and will have a noticeable effect on the temperature in a household, not to mention energy bills. If there is more than one failed unit, heating bills are likely to be higher and there are more issues with damp and condensation on the inside of the window, due to the decrease in energy efficiency.

Inside condensation can cause damp or mould in the worst affected rooms. This usually manifests as green or white patches with discolouration of paintwork and / or peeling wallpaper, usually in the upper corners of the affected room. Residents may also be able to smell the damp as it can emit a rather musty odour.

If they commonly find condensation on the inside of their windows and doors, it’ s