Cold concrete slab can be insulated from outside

Q. We added a room to our house that has only a concrete slab for a floor. The slab gets so cold in winter we are unable to use the room. How can we make the room comfortable? —Vicki

A. Cold concrete floors are a rather common problem and there are several approaches to warming them up. A few of the methods are expensive or not practical for some homes. One of the most-recommended systems requires digging a trench around the outside of the slab to below the frost line, which in some climates can be several feet. Panels of foam insulation are then glued to the perimeter of the footings and the slab. For details on this method, visit and put Slab-on-Grade Foundation Insulation in the search space. In some states where termites are a serious problem, special precautions need to be taken in insulating a slab perimeter, since termites can tunnel through the insulation to reach wood.

A second rather costly method is to retrofit the slab with radiant heat.

Still another method that can add several inches to the thickness of the floor is to attach foam insulating panes to the surface of the floor and cover these with finish flooring. For information on these methods, search the Internet with phrases like Retrofit Radiant Heating and Insulating the Surface of Concrete Slab.

There are a couple of methods that can add some comfort to the room at moderate cost, assuming that the slab does not have a moisture problem. One of these is to lay Comfort Base panels, made by Homasote Corp., over the surface of the floor. These panels are only about 1/2;-inch thick and are small enough (4 feet square) to handle rather easily. Cover the panels with a thick carpet and pad. For details, visit and enter Comfort Base Installation in the search space. Cork tiles, generally about 1/2;-inch thick, can also have some insulating ability and add comfort to the floor.

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