This has always been my experience of the situation. Even on a new build extensions where I obviously build the openings spot on as per drawing:hehe: the openings are measured prior to manufacture.
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There are obviously standard size openings, 1200 x 900, 1200 x 1200 etc, but good luck to a manufacturer making a batch of windows standard size. We know, in the game, that it doesn’t work that way. They’re very rarely timber nowadays where a chippie could run a plane up the sides......haven’t seen a chippie use a hand plane or saw for that matter. They’d rather pick a rattlesnake up than a tool without a lead or battery:hehe:
I won't go to them on principle.
They did my neighbour's conservatory ( a bloody big one!) and sure, it looks ok.
But they extended their workplace into my garden, not so much as a by-your-leave.
Not only that, but they had concrete delivered by a lorry with a snorkel thing; it needed to extend its stabalisers, where did they put them?
Right in the middle of my lawn!. This was in November or December, so the ground was wet, and the stabaliser made a two-foot deep hole in my lawn, so big you could stand in it.
Even worse, the lorry driver buggered off without saying anything.
Only when I emailed the office with a pic did the on-site workers actually fill the hole.
Bastards.
I have always used http://www.misterwindow.co.uk/ excellent customer services and the director is a city fan :)