If applying rigid foam insulation boards, Slash them to dimension and in shape them tightly in between the floor joists. Safe them in place applying building adhesive or mechanical fasteners. Beneath-Joist Insulation: For suspended floors, you could put in insulation substance underneath the floor joists to make a thermal barrier. https://attic-nsulation04789.bloggactif.com/35100459/getting-my-floor-insulation-to-work