Double glazing units.

[pwdrive]

The problem is not the frames.
The sealed units are all the same glass but the spacer/seal varies.
It is not whom you buy them from but where the assembly shop gets the material from.
Larger panes fail more quickly too.

I was told that the main cause of failure is the bottom of the sealed units if they are sitting in water, the bottom spacers in the casements should have a channel or channels on their underside so that in the event of the frame seal leaking the water can flow to the drainage slots in the bottom of the casements, if the drainage slots are blocked and not sorted out the sealed units are doomed so my DG man told me.

Lawrence.