Rigid foam is a nice option because it provides an excellent thermal break between concrete and flooring.
Rigid foam over subfloor.
The foam butts against the mudsills for a complete thermal break.
Leave a 1 4 inch gap around the perimeter.
Two layers of 3 4 inch osb subflooring then float unattached on top of the foam to provide a solid and stable underpinning for the wide board wood floors.
I glued 1 inch thick rigid foam board onto the concrete floor which i had previously treated with a 1 16 inch coating of xyprex moisture proofing.
You can use either one or two layers of plywood or osb and the subflooring can either be fastened to the concrete with long tapcon screws or it can simply float above the foam.
There are several ways to install subflooring above the rigid foam.
Expanded polystyrene eps extruded polystyrene xps and polyisocyanurate are the most used types of rigid foam insulation.
Installing plywood over 1x6 subfloor in preparation for engineered hardwood.
For your install plywood will work fine.
Then i glued osb sheets to the foam board.
Use t g and screw through the foam and the into original floor to keep the large sheets flat.
Use a utility knife to cut the foam to size a hacksaw or drywall saw also work well for this.
Every 8 on the edges and 12 in the center.
The polyethylene sheet becomes part of a continuous air barrier for the home.
While all foam insulation products are derived from petroleum some of the key differences include water resistance r value per inch compressive strength facings permeability to water vapor and evidently cost.
Tape the seams of the foam panels with heavy duty construction tape.
Lay sheets of high density rigid foam over the polyethylene.
Proper subfloor for hardwood in a renovation.