Condensation running down a window

Condensation problems in double glazing

20 June 2019

Double glazing is a modern feature in many homes and is seen as one of the best ways to reduce heat loss and improve your homes energy efficiency. Double glazed windows consist of two panes of glass separated by a layer of air. The air combined with the second layer of glass, acts as insulation against noise and heat loss, keeping your home quieter and warmer than single-glazed windows. However, when heat energy builds on one side, it has trouble passing through this inner layer and this creates the perfect conditions for condensation.

What is condensation?

Condensation occurs when moisture is absorbed into the warm atmosphere of a property and then as the property cools down the moisture condenses on cold surfaces such as on windows or windowsills. Condensation is very much a seasonal problem, occurring during the colder months where ventilation within a property is very low.

What is the main cause of condensation in double glazing?

The sight of condensation within a double glazed window unit is usually a sign that there is an issue with the sealed unit of the windows. Put simply, the edge seal of the window unit has failed in some way and as a result, is allowing moisture to enter the window unit in the form of condensation.

Typically the sight of moisture/condensation within the unit means that the sealant (silica) between the glass and the frame will have to be replaced or renewed. Over time, the silica may harden with age and as a result, may not perform as well as it could do at absorbing moisture.

For condensation to form in a double glazed window the surface temperature of the window needs to be cooler than the air inside the room.If the sealant of the window unit has failed the warm air will enter the gap between the glazing. When the warm air makes contact with the cooler air it condenses. The same process happens also with single pane windows and produces the all too familiar problem of condensation.

What problems are caused by condensation in double glazing?

If the condensation problem is left untreated the condensation can travel down the glass and on to the wall below causing potential water damage. Although the first problem with condensation is “fogging”, which makes the window unit look unsightly, there are more serious problems that can affect your home.

Condensation, in turn, leads to the possibility of problems with black mould or in more serious cases decay in the form of dry rot or wet rot. Black spot mould spores are air-borne and when mould is allowed to grow and produce spores in great numbers, these can create problems in those suffering from asthma or any other respiratory conditions.

Dry rot and wet rot flourish in damp inadequately ventilated conditions, failure to eradicate the damp will see the rot take over your home. Dry rot can readily grow over and through porous masonry, this ability allows the spread of the fungus from one area of the property to another.

Preventing condensation occurring in double glazing

Exposed to wind, pollution, rain and other elements, the best way to stop condensation forming is to take preventative action by checking the seals of the window unit for signs of breakages or hardness. This can be done simply by running a finger around the seal. If any defects are found within the seal then it is worthwhile considering replacing the seal or seeking further advice from a glazing professional.

It is also advisable to check moisture levels within the property as high moisture levels can make condensation problems worse. High moisture levels can be controlled through correct ventilation of the property or through mechanical methods such as dehumidifiers.

Further advice on controlling condensation

The condensation control pages on this website are full of tips and advice on controlling condensation within the property. For further advice or to arrange a condensation survey call your local team on 0800 288 8660 or complete the online condensation survey request form.

Originally published 12th November 2012, updated 20th June 2019.