Expose the underside of the existing floor sheathing. Inspect the framing and sheathing for damage or decay and repair as needed.
Install batt insulation to the depth of the floor joists. Insulation is only needed to the extent of the exposed exterior floor.
Install rigid foam insulation at the end of the insulation where it lines up with the interior space above.
Install gypsum board to cover the floor insulation in an air-tight manner. The inner edge of the gypsum board should extend past, and be sealed to, the rigid foam board.
Seal along the outer edge of the ceiling gypsum board at the exterior wall.
Install spray foam sealant around the rigid foam, sealing it to the floor sheathing, floor joists, and the top side of the gypsum board.
Install additional gypsum boards to finish the ceiling if desired. Tape and mud all joints and paint the ceiling with a vapour-retarding paint.
