First, the plywood or oriented strand board (OSB) subfloor floats on a corrugated or "cleated" waterproof underlayment, so the wood never actually touches the floor. The underlayment material can be made of Styrofoam or heavy-duty polyethylene, the same material used in corrugated plastic drain pipe (one of the toughest plastics available). This underlayment creates an air gap above the concrete. Combined with the wooden panels, the air in this space provides a thermal break that acts as insulation to keep floors and rooms warm. These systems can warm a room as much as 10 degrees. Second, that same layer of plastic provides a moisture barrier against the dampness that naturally rises through concrete slabs.
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