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Outside window pane cracked but don't know the cause.

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iainhtn | 19:31 Thu 15th Jul 2010 | Insurance
14 Answers
I'm just after hearing an almighty bang and came downstairs to find 3 large cracks spanning out from what looks like an impact point on the outside of my double-glazed street facing window. I can't see any evidence of any missile that would have been thrown at it or any suspicious looking gangs of youths hanging about so I'm not at all sure what has caused it. There does look to be damage caused by an impact taking a chunk out of the glass and the cracks spanning it out from it.

So, I guess I have 2 questions. Is it possible that something like this would have happened naturally - stress, fatigue etc...? And what are the options regarding insurance? I have standard house insurance but am unclear whether something like this is covered in it? Does it need to be deliberately caused damage before the insurance guys will fork out? If there's no proof what caused it, what can I do?

Thanks in advance.

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We had double glazing fitted throughout the house in 2004 (wedding present from my parents). About a year later a pane in the main bedroom "exploded" in exactly the way you describe, except it was the inside pane. Had I not been in the house at the time and known for a fact there was nobody in the room in question and it was the internal pane that went, I'd have sworn...
21:42 Thu 15th Jul 2010
Is there a small crater at impact point?
My guess is either a bird, a stone, or if it is not toughened glass ... a pellet .. from an air rifle.
Glass is cheap to replace .. even double glazed panel.
Question Author
Yeah, thats exactly what it looks like. Can't imagine a bird flying fast enough to do it and if it had it would have probably killed itself! So you would guess it was deliberate? Should I phone the cops?
If I couldn't find anything obvious, I would have another search tomorrow. Look for anything as small as a pellet. Of course, it could have ricoched off. Any doubts due to the area, etc, I would let the local police know. They may know something you don't about local goings on!
a pellet will have left a black impact mark on the out facing inner glass i would expect as it's velocity slowed on going through the outer glass, look at the bottom of the sealed unit,l bet there is a BB gun pellet or the remains of a metal airgun pellet
We had double glazing fitted throughout the house in 2004 (wedding present from my parents). About a year later a pane in the main bedroom "exploded" in exactly the way you describe, except it was the inside pane. Had I not been in the house at the time and known for a fact there was nobody in the room in question and it was the internal pane that went, I'd have sworn something had hit it. It was a crack like it had been hit and it had a pattern like it came to a central focus point.

I called the firm that fitted the windows who came round and had a look. They in turn contacted the manufacturer who confirmed they'd had a number of problems with a batch of windows manufactured at that time whereby the pressure wasn't exactly correct in the vacuum between panes and in some cases they eventually simply imploded (technically they cracked inwards, not outwards). They replaced the window free of charge of course and warned it was possibly that any of the others manufactured at the same time might also go. A couple of months later one in the other bedroom did the same thing and was also replaced free of charge.

We've had no problem with them at all in the five years or so since. None of the others ever went.

So, can it happen without anything striking the window? Yes, definitely, I've seen it happen. Insurance? No idea, we didn't need to. If the windows are relatively new and the firm who put them in still exist I'd ask them for comments first. If not, I'd be surprised if property insurance doesn't cover it but it may cost less than your excess to just get it replaced.
Just to add, my tale proves that a window can crack all on its own with all the symptoms you describe. Doesn't mean of course that it wasn't hit by something from outside. I think from what I was told at the time of mine that in the circumstances I describe it would normally be the internal pane that went as it was normally warmer inside than out.
Glass is normally covered on your Household Buildings Policy, but as Skyline pointed out check that your excess, and the value of any No Claims Discount you may receive, do not exceed the cost of repairs.
Question Author
Thanks all. Its really does look like it was hit by something.... the area around where the cracks centre on does look like a chunk has been taken out of it by something small being hurled at it - theres even a very small hole at the very centre. Although the sun never directly hits the window it can get quite warm in this weather so maybe that caused it. I guess I'll see how much it will take to replace it before going to the insurance company. Thanks all - your answers are much appreciated.
Mine looked for all the world like it was hit by something too. Never the less it wasn't.

I don't think you can tell by how it looks. Unless you can actually see what hit it I wouldn't necessarily assume anything.
We also have d/b glazing and we did use insurance to get it repaired. However when it was eventually replaced the guy who fitted it told me it would of been cheaper not to go through insurance as I had to pay £100 excess whilst the glass fitted was only £78. So I'd say get a price first.
Could it have been a stone thrown up from a car wheel?
We regularly get idiot pigeons hurtling into our bedroom window - it sounds like it has been hit by a brick and very ofter we get a complete ghostly image of the bird on the pane - once or twice we have had to replace the glass because of this - we saw it happen and the dying bird disappeared altogether by the time we got downstairs. Any smudges or smears around the damage couls indicate a bird has hit !
What - Kamikaze pigeons ?

Well , I'll go to the foot of our stairs !
Have a look back at the meteorological record for the week it cracked, was the air pressure high/rising, ditto temperature. If the glazing panel was initially set, or had settled in the frame so that there was stress across the pane, then simple temperature or air pressure changes can cause double glazing to implode, more likely if the seal was good and the pressure inside during manufacture was wrong.
It's technically a manufacturing/fitting issue, but really difficult to prove in hindsight exactly what caused it as you now can't measure stress points, what the internal pressure was, or whether there was a small flaw in the glass that contributed to the start of a stress fracture.

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Outside window pane cracked but don't know the cause.

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