Covering houses wiring with insulation is generally OK so long as the protection is correct (covering 'derates' the circuit. That means using contact breakers of the correct type and rating not fuses. If in doubt get a sparky to have a look. The foam insulation works well, but is an expensive option for underfloor.
Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.