You can attach wood sleepers to the floor fill the gaps with rigid foam insulation and then apply your finish flooring.
Rigid foam insulation under subfloor.
Most people do not think about insulating their floors unless perhaps it s their attic floor.
You want it snug but not to.
Or as demonstrated here you can cover the slab with rigid foam insulation add two layers of plywood and then add the finish flooring.
Insulate the band joist with batt insulation as well as the crawlspace access if it s located in the wall.
Not only does it provide high r values but foam board insulation is also easy to install lightweight and can be used in any room of your home.
The top layer of subfloor steps back and gets a layer of peel and stick flashing tape to form pan flashing under the sliding doors.
In other words rigid foam can be applied on walls foundations and roofs and works great for both retrofits and new constructions.
There are two ways to handle insulating concrete floors.
The foam butts against the mudsills for a complete thermal break.
Concrete basement floor.
But insulating your floors is a good idea for many reasons including energy efficiency and height adjustments.
2x4 sleepers installed on center every 12 16 inches and fastened down with rigid foam insulation 1 1 2 inch thick placed between the sleepers.