"vapour control layer nailed to the deck"

[elmsoft]

The plans for my extension specify

"[Thermaroof] insulation to be bonded to 18mm plywood with vapour control layer nailed to the deck sealed with hot bitumen."

I can't quite understand what gets fixed to what, how, and in what order!

Anyone help?

 

[chappers]

VCL nailed to the deck then sealed with bitumen, then the insulation which has ply top deck fixed to all that.
so order from bottom up.
joists
furring pieces
ply sub deck
VCL
bitumen
insulation with bonded ply top deck
roof covering

 

[elmsoft]

Thank you . That makes things clearer.
Is the bitumen heated in a tar boiler and poured over the VCL ? And that bonds the Thermaroof so I don't need mechanical fixing of the insulation?

 

[chappers]

I suppose so, but have never seen it done I would personally skip that bit. In fact my lay up would be ;
joists
furring pieces
sub deck all fixed to joists
VCL
insulation
top deck, fixed through insulation to sub deck
roof covering
if you are really concerned that you have pierced the VCL to hold the deck down, then you can always use a polythene layer under the joists, between them and the plasterboard.
Don't forget to insulate the open voids at the ends of your joists too.