Date posted: 09th May 2018

Triple glazing cost

Triple glazed sealed units are more expensive to manufacture than double glazed ones, as there is an extra chamber to argon gas fill, an extra pane of toughened glass, an extra spacer bar and extra transport costs due to weight and size.  Over double-glazing it just works out as a simple extra square metre cost usually at around £100 per square metre. This does mean that an average 4ft (1220mm) square window would have around 1 sq-m glass. So this would add around £100 to an average size double glazed window.

What is the cost of a triple glazed window?

Whilst our window range is vast and there are many different systems and material choices, if we just stick with our standard white uPVC window system with a couple of openings in double glazing, the installed value including VAT would be around £465 (correct as of July 2019) therefore an equivalent triple glazed one would be around £565, so around 22% more.

Heat-loss through windows and triple glazing

In the UK, houses typically lose up to 20% of heat through the windows. So if you are changing your windows, then fitting the best insulated products is probably the most sensible thing to do. You would need to factor in the extra cost of triple glazing against the saving in heating bills, the payback time will certainly not be over-night, that said a customer once told us "We would like to live as comfortably as possible, so we feel triple glazing is the right product for us" That decision ultimately of course will be yours.

Benefits of triple glazing

There are benefits to installing triple glazing in your home, mainly heat insulation but the important thing to remember is that all triple glazing is not the same. There are many triple glazed systems available but to really get the maximum benefit, the gaps between the panes of glass should be 16mm and filled with an inert gas like argon. Argon gas reduces the heat loss through the panes. If the gap is reduced then the thermal performance of the sealed unit is reduced, unless you start to use an expensive gas like krypton. So the optimum size of a triple glazed sealed unit should be 4mm glass, 16mm gaps, so in the glazing industry it’s called a 4/16/4/16/4 unit and that equals 44mm in total. If you just compare the u-values (heat losses) of the glass then the comparison between 44mm triple unit and a 28mm double glazed unit is large. The typical centre pane u-value of the 44mm unit is 0.62, the double glazed unit 1.1, so over a 40% improvement.

Triple glazing Energy Rating

You can choose a window based on how many panes of glass it contains, however you should first look at the Window Energy Rating (WER) This is a more reliable way of predicting how thermally efficient the windows will be once they’re installed. WER’s are the UK’s standard method for calculating how much heat will be lost through a window.

The WER takes into account the following:

  • Air losses through the windows
  • The U-value is a calculation of how thermally efficient the entire window is, using both the glass and the frame material.
  • The amount of the sun’s heat that passes through the glass to warm up your home. In most cases triple glazing does not enhance solar gain over double glazing, a well-insulated window works well at retaining heat, but not so well at allowing solar gain.

Triple glazing cost summary

So triple glazing does cost more than double glazing, working on our calculations above then as much as 22% more. However these are just KJM’s costs, generally if we are compared to say a ‘national’ glazing company then we are usually much cheaper for both double and triple glazed windows. Some of these larger companies may well be offering ‘free upgrades’ to triple glazing but what is the starting point for the ‘base’ product? If you double the starting price then a 50% discount brings you down to a sensible starting point! With this in mind it is always worth, in my opinion, seeking another quotation.

Swissspacer warm edge spacer bars


Finally triple glazing can offer thermal efficiencies with over a 40% improvement over double glazing, the payback time may well be quite a while, however these extra costs could well be recouped if and when you come to selling your home.

You can read my triple glazing blog post for further information.