Best insulation for loft joists only 250mm apart?

[RedBeardPete]

We've bought a 1920's house and want to renew the insulation on the floor of the attic. The gaps between the joists vary in width(!!) but most are 250mm apart and 100mm deep. Don't particularly want to have to put in more joists to use loose fill and I know that I shouldn't really squeeze standard 400mm width roll into the gap as this would squeeze the air out of the roll and thus reduce thermal efficiency.
Do I just buy standard width roll and start trimming? Or is there somewhere that does narrow roll that I don't know about?

Thanks

Pete

 

[JohnD]

you can buy a wide roll (about 1200mm) and cut it with a saw or breadknife to whatever size you want. It is easier to cut while it is still rolled up in its wrapper. You will need a dust mask.