Following on from my previous post (Why being a Web Developer is interesting…), I thought I’d write about something I learnt recently whilst developing a website for a local building and joinery contractor, who amongst other things, installs upvc double glazing.

During our discussions about his website design, he passed on a few interesting tit-bits relating to the building trade and this is one of them.

Not Vacuum Sealed?

The first revelation was that double glazing is not typically vacuum sealed. It is sealed with the intention of being air-tight however and although not a vacuum, the pressure inside will often be different to that outside.

As could be expected, the air that is sealed within the unit will have naturally occurring moisture within it, so why you might ask (and I did) do you not get condensation within the windows from the start?

Secret Silica Gel

The answer? The second revelation I received was that the brown (or black) metal strip that you can see inside your glazing running the length of the seal contains thousands of silica gel crystals. It is perforated with holes to allow the crystals to absorb water moisture from between the sealed panes.

This means that inevitable small breaks within the window’s seal can be tolerated up to the point at which the silica gel becomes saturated. After that, the windows are considered to be ‘blown’ and need repairing / replacing.

From reading further, I gathered that the length of time double glazing lasts depends on the quality of the seal, whether it is damaged during installation, whether water can freely drain from the frame so that it does not submerge the seal for any length of time, the amount of water moisture sealed in the unit to start with, the amount of silica gel used within the seal, the area in which you live and which direction your window faces.

Further Reading

Note, this information is recounted second-hand and although I have a passing interest, I don’t claim to be a scientist. If you want to know more or be sure of your facts before boasting in the pub, do a Google search or take a look at the following sites:

And for anyone who is interested in the green credentials of double glazing, this website discussion is worth your while:

And that’s it! You may have already known this or you may not care, but it was certainly news to me…