How to Build a Heated Concrete Floor

Check that the subgrade is level using a laser level. Fill in any low spots with crushed gravel and tamp down until compact. Lay down a poly vapor barrier on top of the subgrade to help prevent moisture vapor from coming up through the concrete slab.

Place a 2-inch-thick layer of rigid Styrofoam on top of the poly vapor barrier. Place flat sheets of wire mesh on top of the Styrofoam. You will be using this mesh to keep the radiant-heat tubes in place.

Lay out the radiant-heat tubing according to your tube installation diagram. Tie the radiant-heat tubes to the wire mesh using plastic zip ties or wire ties. Connect the tubing to your hot-water source according to the manufacturer's recommendation. Turn on the system to check for leaks. Fix any leaks found. Turn the system off for the next step.

Pour in concrete until the radiant tubes are covered by the concrete. The floor should be at least 2 inches higher than the radiant tubing. Drag the screed across the concrete to level the surface of the floor. Check the floor with the laser level to ensure that the floor is flat and level. Once the floor is level, smooth the floor by pushing a bullnose float back and forth across the surface.

Allow the concrete to set and harden for at least one week before using the space. You can stand on it after 24 hours, but at this stage the concrete can chip and break easily.