Hi

The builders have used kingspan boards between the roof joists - do you also recommend using typical wool type insulation or will the kingspan be ok? The space up there isn't massive.

Thanks

It's 100mm - not sure about the gap behind it.

Size of the rafters - no idea I am afraid  
I've heard kingspan is good stuff, my only worry is that the loft area will be warm and the rooms will be cold and there is nothing to stop the heat from going into the loft as there is no insulation directly onto the celing.

The old loft space now contains a 2 bedroom and a bathroom (Dorma extension) the there is now a new little loft space above. I wouldn't even use it for storage to be honest. I didn't want to over insulate in case is causes sweating. Something the builder mentioned. He's said there is no requirement for wool up there as the kingspan is fine.