A-rated windows - exterior condensation is normal.

It seems that some homeowners are experiencing condensation problems with a-rated double glazing, only in this case, the condensation is on the outside.

The problem stems from the fact that the windows are so efficient at keeping the warmth in, the outer pane of glass is dropping in temperature, leading to condensation forming on the outside - it's been likened to coming out to your car in the morning and the condensation you find on the outside of the car windows.

When you're having an a-rated window installation, your installer should explain that this is a natural occurrence and that whilst the condensation may seem unsightly, it usually burns off as the morning progresses.

The effect is most evident during the Autumn and Winter months when night time temperatures fall lower.

Like your car windows, windows that are shaded by overhanging bushes or low trees or face the sunrise will clear quicker / not condensate as much.

And it's not unheard of for windows, even on the same face of the house, to clear at different intervals as the outside pane warms up, dispelling the moisture.

The temperature of the inside of the property will also affect how quickly the condensation clears. Even though a-rated windows use a particular form of spacer in the manufacture of the sealed glazing unit itself that doesn't transfer heat as much as normal c-rated glazed unit spacers, some heat transfer is inevitable.

In really low temperatures, exterior condensation is likely to freeze - again, just like a car window.

Whilst a-rated and coated glass is generally as tough as ordinary glass, it can scratch if wiped or scraped with stones etc trapped in the cloth or other surface you're using so take care.

if you're worried about the issue of condensation, you could explore fitting a less efficient window e.g a c-rated design.

Of course seeing condensation forming on your new windows can be a bit alarming, however a call to your installer is usually enough to reassure you that it's a normal part of owning the most advanced, thermally efficient windows on the market today.

The market is already aware of the problem and ideas like a form of self-cleaning coating (like the kind currently available which encourages rain to 'run-off' windows) will no doubt be explored. In the meantime, a little condensation is the price for ultimate energy efficiency in the home.

We've not read any reports of similar issues with c-rated windows, however the more thermally efficient a window is, the more likelihood it will suffer some form of exterior condensation.