|Pilkington Spacia is one of the new generation of high performance vacuum windows|
Vacuum glazing has now appeared on the UK market and will be sold into the heritage market as a highly energy efficient option for windows where thin glazing is needed – sash windows etc.
On the face of it these are amazing windows, very low U values (so very good thermal performance) and easier fitting in thinner, older frames that cannot take modern double glazed units. So all well and good. However, there is a major issue that is not looked at in the brochures – Time.
Nature does not like a vacuum. So what happens to the window performance once the vacuum has failed?? Some of the manufacturers state that there is a 10 year guarantee period and that the windows are expected to last longer. To me I don’t think that people will be aware of when the windows are no longer working properly and also the idea that you have to replace your windows every decade or so seems like a waste of resources / money.
I fear that this is a well intended energy efficiency exercise that might have unintended consequences. I think that it will lead to even poorer calculations in EPCs after a couple of years as they will be adjusted to take the windows original value, not its actual value at the time (this would be impossible to calculate easily). Later homeowners will be told that the windows are super efficient, but actually they will probably be very inefficient.
CADW have shown that single glazed windows can be improved radically by using secondary glazing, draught proofing, heavy curtains and shutters. So the expense of fitting vacuum glazing might be better spent on these improvements in the long run.