Condensation within and around your home can occur for a variety of different reasons.

But we‘re going to focus predominantly on why and how it forms on your windows and doors. Whether or not you should be concerned by condensation on your glass units - and what you should do to resolve it - depends largely on where it is forming: on the outside pane, on the inside pane, or in between the panes.

What is condensation - and why does it occur?

In brief, condensation is the physical process by which a gas or vapour changes into a liquid. When air contains more moisture than it can hold the moisture turns back into water - this is known as the saturation point. The temperature reached at this point is known as the ‘dew point’ and this is when the air is cooled to become saturated with water vapour, allowing dew to form. 

If the temperature of an object falls below the ‘dew point’ temperature, then water vapour from the atmosphere will condense into water droplets on its surface. The ‘dew point’ varies depending on the temperature of the air and the amount of water in the atmosphere (relative humidity). In terms of the glass units in windows and doors, the variation between the internal and external temperatures, and indeed of the glass itself, is what causes condensation to form. 


Let’s start by discussing condensation on the outside pane of glass. We are often asked whether condensation on the outside of newly installed windows and doors is a product fault, and the short answer is ‘no’. So, why does it form in this way? Because of the thermal efficiency of your new windows and doors, the heat from inside the property does not escape to the outside pane (as would be the case with less efficient units) and so this outer pane often drops below the external dew point temperature. This means that water vapour from the air will condense on it. 

While condensation on the outside pane of your glass units may be an annoyance, you can expect to experience it if your windows and doors are performing well (depending on atmospheric conditions). As external conditions change, the condensation will disperse and so it is not necessary to take any action. 


If condensation on the outside pane of your windows and doors is a sign that they are performing well, what does it mean if you have condensation on the inside pane? Condensation on the internal pane of your glass units may be the result of inefficient windows and doors, but can also be related to living conditions and inadequate ventilation within the home. Replacing your existing windows and doors with thermally efficient ones may go some way to reducing condensation on the internal pane. This is because considerably less heat will be lost through the glass, from inside to outside. This means that the inner pane will likely stay warmer, meaning there is a far smaller chance that it will drop below the ‘dew point’. 

However, if you have inadequate ventilation and / or insulation in your living areas (particularly in rooms such as a kitchen or bathroom where humidity levels are high), you may still experience a degree of condensation on your inner glass panes, no matter how efficiently your doors and windows are working. High levels of condensation inside your home can pose a greater problem, particularly if it is followed by mould, and you should seek expert advice in such circumstances.

Condensation in the middle

Also known as interstitial condensation. If you have double or triple glazed windows and doors - particularly older styles - you may notice that you have condensation forming in between the glazing units. This is caused by the failure of the airtight seal and means that the gas cavity is no longer impermeable. This is commonly referred to as a ‘blown’ or ‘foggy’ glass unit and it should be replaced in line with the terms and conditions of the product’s warranty. 


Sometimes, if your home has a wider condensation problem, it is resolvable without needing expert help. Equally, though, it's also worthwhile knowing when to call in the professionals. For further information on condensation within your home try visiting the links below:

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