Mystery cracking of double glazing.

[Trixie2]

Over the last year two inside panes of my double glazed windows have, for no apparent reason, cracked. The first went off with a bang and fell to bits. The second just developed a lot of cracks which I didn't notice until I was cleaning it. Anyone else with the same experience or suggestions as to the cause?

[johnk]

There may some weight onthem if your lintel was removed orhas failed or if you don't have one and the wall above is beginning to sag. Take a look outside, are ther any cracks in the plaster inside?

[Trixie2]

Nothing evident johnk. The broken panel is fitted in the sash which opens and closes easily so no pressure there. Many thanks for the reply.

[123everton]

May be some movement, twisting, with the property, sounds like a lintel problem though.

[The Builder]

Mmmmm .......... very unusual Trixie. You mention a loud bang which suggests the units have toughened inner panes. The glass is heat treated to toughen it. That means that they live their lives under stress (quite normal).
I can only guess that something went wrong in the toughening process that wasn't visibly apparent.
You obviously need to replace them anyway. Unless they are "nicked" by a nail or something when fitted, they should be fine.

[KARL]

If the glass is toughened (same asa in some car windows) then there just may be something wrong with it. However, another possibility is that stress is being raised on/in the glass by sealant between it and the frame - the sealed unit should be free to move (expansion/shrinkage as well as flexure) in the frame. This is an installation issue. Another possible cause would be if there is some fundamental flaw/defect in the manufacture of the sealed units themselves (a supply issue). To establish the actual position you may need to seek the advice of a good buildings inspector (not someone with a vested interest, such as your installer).

[Trixie2]

Great responses. Unfortunately they haven't really solved the puzzle. I should have mentioned that these have been in situ for eleven years, without previous problems? Many thanks for the contributions.