Over the past 10-15 years, with the advent of more thermally efficient windows, one phenomenon has become more and more popular across the country and that is external condensation.

That is condensation that forms on the outside of the outer pane of newer double glazing. But why does it happen? When can it occur and should anything be done about it?

How external condensation forms on windows

External condensation on energy-efficient windows is actually a sign that the windows are working. You are most likely to see this effect in the Spring and Autumn when outside conditions are just right.

It can be quite alarming to see your windows fully misted up in the morning. But rest assured, these are your windows working, and in an hour or two with a bit of heat and sunlight the condensation goes.

But how exactly does it form? This is a technical explanation from Pilkington:

What Causes External Condensation?

Condensation is caused when the outside temperature of glass is lower than the temperature inside. Cold nights and dropping temperatures result in the formation of water vapour on the external outer panes of windows.

Moisture condenses out of the air onto a cold surface at what is known as dew point. The dew point temperature is the temperature at which the air can no longer “hold” all of the water vapour which is mixed with it. Some of the water vapour at this point must therefore condense into liquid water.

Typically in the spring and autumn months, the dew point can be comparatively higher, causing condensation to occur more regularly.

Condensation and Modern Glazing

Condensation on the external surface is becoming more common as the types of glazing units being fitted into homes today are much more thermally efficient than in the past. The more thermally insulating the glass is, the lower the outer pane temperature is likely to be and the greater chance condensation will occur on external surfaces. With traditional style single glazing and older style double glazing, a large proportion of heat was lost to the outside through the glass.

So there is no need to be concerned if you find your new windows have external condensation from time to time during the course of the year. But it should be something you are aware of and it may be something that your chosen installation company will want to explain to you.

Is there a solution?

If external condensation is something you want to try and avoid, major glass manufacturers Saint-Gobain and Pilkington have brought out their own glass variations designed to combat external condensation. Saint-Gobain called theirs SGG VIEWCLEAR® II and Pilkington called theirs Anti-Condensation Glass.

The reality though, is that anti-condensation glass isn’t a huge seller within the UK fenestration market as there isn’t a great deal of demand. From experience most people are happy to live with it, knowing that it’s a sign their windows are working well for them.