Seal and insulate floors that overhang the foundation. It is usually possible to remove the finish underneath the overhang and air seal the space between the joists above the foundation with polyurethane foam or with caulked, low-permeability rigid insulation. Insulate the joist space with batt or blanket insulation and add an air barrier before re-installing the finish.

In some cases, a layer of rigid board insulation with protective outer finish can be applied to the underside of the overhang, but the space should still be air sealed and insulated. Alternatively, a contractor can spray foam into the cavities or blow in dense-pack fibre insulation though holes drilled to the underside.