There is no such thing as A Rated Glass

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Nick Dardalis

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Are you aware that there is no such thing as “A Rated Glass”?

Bear this in mind if you are in the process of buying new windows or doors. If you are seeing advertising material, or you are being advised by a double glazing salesman, that their windows and doors come with A rated glass then you can be certain this is not the case.  And here is why:

The energy ratings of windows (also known as WER’s) are generally represented by energy efficiency labels similar to those found on energy performance certificates on home appliances, property particulars and windows and doors.  Any item that has an energy rating applied to it is generally tested as a complete product.

In the case of new PVCu or aluminium windows, Window Energy Ratings attached to these are achieved by testing the complete product which includes the window frame, double glazed units and window gasket.  Therefore any product called A Rated is the complete window. A specific element of any window cannot on its own be A rated.

Beware of misleading information relating to A Rated windows.

You may also be advised to upgrade the glass on double glazing to triple glazing, A Rated or other descriptions.  Unless the company can prove with documentary evidence that the whole window has been tested with the glass upgrade they are proposing then there is no guarantee you will get a window with the performance figures promised.

Where some companies are offering free upgrades to triple glazing, you may assume that a triple glazed window is automatically more energy efficient than a double glazed window.  The performance figures between the two products are not that great as stand alone glass without a window but can make a difference when tested in a complete window.  Therefore again be aware that simply upgrading the glass will not give you the expected Window Energy Ratings unless that complete product has been officially tested.

Why A rated glass may not produce an A Rated Window

Within the double glazing sector it is commonplace today to describe glass specifications in marketing material and window brochures.

A very popular glass specification is:

4mm Clear Float one side with a 20mm cavity with Argon Gas Fill Spacer (90%),  a Swiss V Spacer Bar  and 4mm Softcoat Low-e to the other pane of glass.

Typically, this standard and quite common glass specification will achieve a U Value of 1.2 W/m2K and popular PVCu windows tested with this glass specification will in most cases achieve a Window Energy Rating of A.  However if this same double glazed unit was fitted to an aluminium or timber window you will not get an A rated window in these materials.

This message is also being reinforced by The British Fenestration Rating Council.

The British Fenestration Rating Council (BFRC) has also recently commented on misleading material and claims made by window companies or window sales people.  Dr Gary Morgan, Technical Director of BFRC says:

There is no scheme in the UK that rates glass in isolation.  All WER schemes operate in an identical way – rating the whole window including glass, frames, spacer bars and gaskets. It is not possible under current European Regulations to provide an energy rating for glass in isolation from the other window components. Whilst it is true that certain glazing specifications are widely used in ‘A’ and ‘A+’ rated windows, the glazing itself does not guarantee an ‘A’ or ‘A+’ rating for the whole window. The frame system also has to be thermally efficient to enable the complete window to obtain a favourable rating.  Claims of ‘A-rated glass’ and the like are obviously designed to give the impression that the window itself is ‘A’ or ‘A+’ rated, which is misleading.

Therefore you should be very careful if any window company is mentioning A Rated Glass rather than the entire window.  You may challenge the window company on this and you may be then told that of course the whole window will be A rated, but we must stress that unless the tests have been carried out on a complete window and you have the documentary evidence to prove this, it is likely you may not be getting the product you expect.

This is particularly the case with Aluminium Windows.  These are available with an A rating although many systems only offer a C rating that is still compliant with the Building Regulations. You must tell your window company if you specifically require A rated aluminium windows and not presume that they will be.

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