Insulating extension rafters - foil tape over first layer?

[zeroid]

I'm currently doing the insulation for newly built kitchen extension that has a pitched roof. This is being done to building regs - 100mm celotex (GA4100) between the (150mm) rafters, coming flush to the internal face of the rafters, then another 50mm + 12.5mm plasterboard will go over the top (I'm using PL4050 for this).

I've friction fitted the 100mm layer between the rafters and I'm foil taping where celotex edges meet each other. Do I also need to foil tape over where the celotex meets the rafter? How thorough does this need to be given the PL4050 is going on top? Should it cover the rafters entirely so its all foil and no wood showing?

Thanks...

 

[freddiemercurystwin]

You only need a vp between the PB and the insulation.

 

[noseall]

We foil tape and foam everything. But I've always been a belt and braces kinda guy.

'Robust' is the word of the day.

 

[zeroid]

The plasterboard is bonded to the 50mm insulation that's going on top, so I guess that wont form a vb, and means it would be a good idea to tape all over this layer.