Foam board insulation is used on attics and walls yet it can also be used to insulate your floors.
Rigid foam insulation under subfloor.
The foam butts against the mudsills for a complete thermal break.
Concrete basement floor.
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.
In other words rigid foam can be applied on walls foundations and roofs and works great for both retrofits and new constructions.
Or as demonstrated here you can cover the slab with rigid foam insulation add two layers of plywood and then add the finish flooring.
Most people do not think about insulating their floors unless perhaps it s their attic floor.
You want it snug but not to.
You can attach wood sleepers to the floor fill the gaps with rigid foam insulation and then apply your finish flooring.
There are two ways to handle insulating concrete floors.
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.
The polyethylene sheet becomes part of a continuous air barrier for the home.
But insulating your floors is a good idea for many reasons including energy efficiency and height adjustments.