Reentrant wrote:
Our double-glazing is about 16 years old, and in the last 6 months
three units have failed with condensation inside. All the failed
units are south-facing - presumably the more extreme heating cycle
weakens the seal eventually.

1) What's a reasonable lifetime for a DG unit?
2) Would K glass help to extend the life of a south-facing window?

I think how well they're assembled in the factory has a greater influence
rather than the glass. You see a lot of big windows that have been sealed
when lying flat which results in concave windows. This not only looks naff
but I think causes them to fail more quickly than those that are sealed
upright. [1]

Tim

[1] I could be talking boll*cks but it seems palusible to me. ;-)