I have 900 square feet of loft to insulate and various rolls of 100mm rockwool that someone has left behind. There is lots of old rubbish and broken glass left between the rafters and the gaps are quite small rectangles. The space between the rafters does not appear to be standard and so to do it properly I'm going to need to cut every roll down to size. It's going to take days and is a daunting prospect.
So I'm tempted not to cut all the rolls to size in order to get the stuff between the rafters. How 'bad' is it if I just lay the rolls across the rafters? I was wondering if ending up with an air gap might actually end up being better? I wasn't planning to put the extra 170mm across the top of the rafters to conform to current specifications as I was led to believe it doesn't actually result in much extra saving beyond the first 100mm.
Alternatively are there any other options?
Any advice or information gratefully received!