On Monday, 5 October 2020 at 09:58:17 UTC+1, Dave Liquorice wrote:
On Sun, 4 Oct 2020 15:00:43 -0700 (PDT), Tricky Dicky wrote:

... the plan being to fit the Celotex between the joists and fill any
gaps around the edge with PU foam. However, some of these gaps also have
cables passing through so just to check does PU foam react like
polystyrene with PVC?
Donno but I'd side step the issue by cutting the celotex to be a snug
push fit and simply taping any joints. Foamed in would make any
future access behind the insulation a right PITA.

--
Cheers
Dave.
Dave I have two joists very close to the wall where the cables are passing below the floor. On one I can do what you suggest and was going to use the PU to fill any gaps. On the other wall there is very little space, although I will try to do as on the other side but suspect the time saving element will be simply to PU the gap.

Richard