Sash windows: what glazing to choose?
Added: (Sat Jan 21 2012)
The days of single glazing are over in the UK. Well, actually, not quite. It depends, as so often in a highly regulated market.
Glazing regulations have changed regularly in the UK over the last 10 years, and this is unlikely to change any time soon. Ever stricter glazing technology requirements of course often, if not always, clash with conservation laws, having left sash windows buyers confused as to what the UK lawmaker actually wants him to buy.
The national rules, as such, are quite straight-forward, and then the exceptions kick in of course.
Since October 2010 the current law clearly states that all new window units, whether they are traditional timber sash windows, or PVC units, must b fitted with B-rated glazing, as a minimum standard. This standard used to be for C-rated glazing before, so this has meant a tightening of standards for the industry.
Now what glazing is B-rated? Simple: it’s either 4 x 12 (cavity) x 4mm glazing, with Argon gas, or 4 x 8 x 4, with Krypton gas filling. Given that Krypton gas is a rare gas, and is about 900 times more expensive than Argon, quasi all glazing nowadays is of the 4 x 12 x 4 mm glazing type.
So far, so clear!
But if your property is listed, these rules don’t apply! So if it is listed, then you’ll have to replace it with like-for-like single glazing. But, for those who hate the idea of replacing sub-standard units with new sub-standard units, one can try and convince (and more and more this is accepted!) the listed buildings inspector of a specific type of glazing (often called “slimlight”), which is in effect a 4 x 4 x 4 glazing type, where the cavity is so narrow that it’s barely visible, and hence is an acceptable compromise. But it will only be acceptable if the spacers within the cavity are white! Otherwise the effect will be ruined, and most inspectors will refuse it. This type of glazing is often more expensive, as all these windows need to be hand-crafted, with special mouldings only for this type, given that the standard is now for 4 x 12 x 4 glazing. But then again this is also true for single glazing, which, for the same reasons, also costs more than double glazing these days.
If your property lies within a conservation area, the national rules might, or might not apply. This depends on the local council’s rules, and they vary. So if your property lies within a conservation area, then always apply for permission, and look up the requirements locally. Often the requirement is for 4 x 8 x 4 glazing, but this is by no means always the case.
Sollex Products ltd.
35 Lichfield Road
Brent
NW2 2RG, London
Telephone: 020 845 289 65
Email: enquiry@sollex.co.uk
http://www.sollex.co.uk/