Anyone know the best way to join PIR to itself to prevent thermal bypassing caused by even very tiny air gaps?
Is it practically possible to tape the underside edges together?
I am thinking of using the same expanding foam tape that I have used in between all my insulated timber-frame wall panels.
Kingspan's Thermafloor TF70 product installation guide says to lightly butt together, which would surely reduce its effectiveness considerably.
I would rather not use PIR at all (I'm not using it anywhere else in the build) but it seems the only option due to difficulty of excavating the ground floor deep enough without disturbing the ground under the existing old stone walls.