Despite much reading of suppliers PDFs and head scratching there are still areas of uncertainty:-)
Current thinking for the screeded area is to use self adhesive clip rails over the Celotex foam. Spacing between rows seem to vary from 750mm to 2.0m depending on source. Question for the chemists... what is the surface coating on the aluminium foil? Cleans off readily with acetone and accepts the supplied tape readily but *duct tape* needs it cleaned off first.
Floor heating suppliers provide a thin foam perimeter sheet to provide expansion space for the screed but Celotex show an upstand of PIR foam to insulate perimeter walls. Do I use both?
There may be more to follow...