Loft insulation/ ceiling boarding

[23vc]

Evening all
I need to put the loft insulation (2 layers of 150mm loft roll) up and board the ceiling on my extension. Last time I did this it was chunky six inch joists so I put a layer of insulation over them then put more between the joists which tended to stay put so I could then board it.
This time it’s trusses so a lot smaller depth on the ceiling cord, just after some advice on how best to do it, can I put 2 layers laid across the Trusses and not have any between, leaving an air gap between ceiling board and insulation? Or am I best fitting each 6x3 board then put the insulation above it?
I’m sure trial and error will probably tell me but any advice welcome
Cheers

 

[John D v2.0]

You can't leave a gap between your air barrier (ceiling pb) and your insulation layer. This can cause thermal bypass ie cold wind blowing on the warm side of your insulation.
Traditionally you would board then insulate but you can always hang it on nets or staple wire across or something.

 

[23vc]

Cheers John