There is another problem with the spray foam but I don't have much more than sketchy memories. The foam must be applied under very strict and narrow conditions. We have seen the jacket of Loomex (Canadian Romex) damaged by foam that was either too hot or cold when sprayed in? The jacket became brittle and would break or crack at bending. Sorry it is a little cryptic. If I had a preferred way it would be ENT (smurf tube) and pull wires in after. As for derating? Not until there are more than 3 - 2 wire cables in contact for at least 2 feet. NMD90 is approved for installation in thermal insulation so single cables would not require derating.
