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Question about crack in double glazing unit.
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latheturner
Newbie
Join Date: 14/07/2010
Posts: 2
Location: Coventry, UK
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Posted: 14/07/2010 9:39:09 PM
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Hi, I have a few questions you'll probably think are stupid but I know next to nothing about double-glazing and would really appreciate some help.
A few nights ago, we woke up to find a crack in the bedroom double glazing unit, on the inner pane all the way from left to right. The crack seem to have started at the right edge of the panel and had a peculiar shape, sort of spiralling. Now that night there was a considerable temperature drop, it had been hot all day long with temperatures near the 30s and went down to somewhere near 10-15 degrees.
For this reason I immediately suspected that it was some sort of thermal stress. I've seen this happen but never on double glazed windows.
My landlord however brought his own double-glazing expert with him who laughed at me and told me double-glazing windows do not crack under changes in temperature, and that we must have thrown something at the glass. The expert is incidentally the landlord's cousin and I really am suspecting that he's lying so that I fork out the cost of the repairs (which is considerable).
So I'm wondering, is it possible for double-glazing to crack like this in the British climate? If not thermal, is there some other cause for this sort of crack? I know I certainly didn't throw anything at the window. Probably I'll ending paying for the repairs anyway (tenancy laws seem to favour the landlords here), but at least I'll know I'm not crazy.
Thanks for any help,
Andrew.
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goodwood
Beginner
Join Date: 14/06/2010
Posts: 11
Location: Rugby
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Posted: 15/07/2010 9:39:34 AM
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My garage window has a crack exactly like that (it's the only plastic window on the property), and yes, I believe it's a stress-crack, possibly because the glass has not been fitted properly, and pvc has such an enormous co-efficient of expansion. I'm not knowledgable about pvc windows, but Terry The Windowman was. He's retired now, but although the forum has gone, his website lives on with a massive store of useful information. I know he could explain your crack. I saw him refer to such problems on many occasions. Google "the windowman" and you'll probably find it easily. He discusses the issues in the section "why did my glass explode?".
Incidentally, the cause of the failure may well become evident once the beads are removed. There may well be a source of stress at one point on the edge that triggered it. Possibly at a packer, or maybe an edge defect where the glass was cut.
KJN
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latheturner
Newbie
Join Date: 14/07/2010
Posts: 2
Location: Coventry, UK
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Posted: 15/07/2010 10:13:16 AM
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Thanks so much for your reply. I googled "the windowman" and the relevant pages turned up including a detailed explanation of why windows explode. This pretty much agrees with what I'm thinking.
The guy that came to repair the sheet smashed the pane immediately, probably to avoid us getting any second opinions. I will have to pay for this window which is very costly apparently. Still, I'll be prepared if this ever happens in the future.
Thanks for your help,
A
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goodwood
Beginner
Join Date: 14/06/2010
Posts: 11
Location: Rugby
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Posted: 15/07/2010 8:00:48 PM
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Glad it explained the problem, even if it didn't save you any money. It might help someone else, one day. Incidentally, this seems to be related to DGUs in PVC windows. I have never come across this problem in wood frames. Sort of confirms my view it's more to do with the expansion/contraction of PVC rather than with thermal stresses in the DGU.
KJN
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