PIR insulation fixing - advice

[pixiepoo]

Hi,

We are currently at the insulation stage of our two storey extension (doing it ourselves) and just want a bid of advice/clarification before I go ahead a get it all wrong!

Am I along the right lines installing the below?

Roof
PIR in-between rafters: cut the boards slightly smaller so there is a gap that I can foam around the edge
PB backed with PIR under the rafters (going into room with sloping ceilings): fix with plasterboard screws into the rafters. How do you seal the joints of two plasterboard/PIRs together?

Ceiling of 1st floor rooms
PIR in-between joists: does this need to be foamed too like the rafters?
PIR over the joists in opposite direction to the PIR beneath: do the joints just need to be foil taped?

Internal wall
An existing internal wall needs to be insulated from inside. We have bought PB backed with PIR, what should this be attached to the block wall with? Dot and Dab or PU glue? We can’t use battens as we are tight on space. Again – how do I seal the joints?

Everyone talks about foil tape but I am unsure what to purchase. I have typed into Google ‘aluminium foil tape’ and there’s loads out there, should I be looking for something special or are they much of a muchness?


Thanks in advance for all your help!!

 

[Lfcsixtimes]

please delete

 

[oldbutnotdead]

Roof- are you planning on living in the loft space? If yes then yes insulate between and below rafters, make sure there's an air gap above the between rafters insulation. Up to you whether you foam the gaps or cut the boards right and foil tape from boards to rafters.
Joints between insulated pb- butt them up tight.
If you're living in the roof you don't need to insulate between 1st floor and loft. If you still want to, use rockwool- much cheaper and easier to draughtproof.
Internal wall- whichever suits you (dot & dab will cost you 10mm or so, glue less).
Joins-again butt them up tight is as good as you'll get.