I think, and the glazier agreed, that it was probably caused by heat getting trapped by the blackout blind we put up in my son's room. The room is east facing and there is no shade so it gets properly blasted by the sun from very early in the morning.
I'm going to have to have a conversation...
I just want to pick the NSC hive brain.
The main double-glazing pane (inner) in my son's room cracked the other day, so I need to replace the unit.
I'm arranging for a couple of local firms (I live in Surrey) to come round and price up the replacement, but what sort of cost should I be looking...