Quote Originally Posted by Optimistic Nick View Post
Ignoring the obvious (and acknowledged) BC and PP issues here, I can't quite get my head around this. What are these 75x50 CLS "joists" bearing on? Surely they cannot be spanning anything so presumably these are actually resting on an existing slab? If so - I can see the logic of the DPM but why bother with the joists at all? Why not just float the P5 on the PIR? And to be honest at 50mm for floor insulation- why bother at all? The heat saving through the floor will be negligible, but surely most of the buildings you are doing this to are limited to 2.5m height and so even a 63mm loss of headroom is sub-optimal?
you are right they just sit on the slab, so no span / load bearing issues, 2 reasons for doing this

1. i have always done it like that, in the 90's people used to use polystyrene jablite batts

2., i run 32mm waste pipe from corner to corner under the floor ( i understand the required fall will not be achieved ), this is done for 2 reasons, if a client wants to put a washing machine in the corner, they can , if they want to run cables at a extra date, its easy to do, i just up turn the 32mm waste pipe and it lives behind the stud wall


Now the reason why i put insulation in, people like the idea of it, we are sold the more the better, a nice insulated floor ( despite the heat loss on the floor being very little )

Most garages are higher that 2.5M as they would either have been built with the house or needed PP to be built, i would guess that the height is most often than not 3M high inside