Pressure-treated sleepers and Expanded polystyrene foam insulation (XPS) isolate the subfloor from the slab
This animation shows how to insulate a basement slab to thermally isolate it from the subfloor, helping to create a comfortable living space
Video transcript:
A basement is a cheap place to find living space because it is already built. But the slab and concrete walls are always going to tend toward cool, so before laying down a subfloor, create a thermal break.
The first step is to insulate the edges along the walls so that the floor is isolated.
Pressure-treated sleepers provide backing for subfloor
Lay down a pressure-treated 2x4 sleeper. You could rip it in. Half if you want to use 2x2s, too.
Lay more of them every 16 or 24 inches on-center. This drawing is 16, but wood is free in animation land.
Add a strip of expanded polystyrene insulation between the first two sleepers and then fill in between the rest of the sleepers.
If you live in a reasonably warm climate, that’s all you need to do before screwing down some subfloor.
Double the insulation layers for cold climates
If you live in a chilly climate, add another layer of sleepers perpendicular to the first and more XPS insulation between them.
It should be obvious that the insulation is the same thickness as the sleepers, but if it is not, it is.
Now you can lay down that subfloor and walk around on it, because any way you look at it, this is a warm floor.