80mm screed is a decent thickness, so you shouldn't have any issues there. :-)
Cheers. Nick. Yes we're using 100mm recticel for in between the trusses, then 50mm recticel to go over that. It's looking like we'll have some of this left over. Can I use these two combined for the floor, or do I need to but the 150mm insulation and do it in one piece?