Buyer worried about radon gas in home
Q. After buying my home, I had new carpets installed. When the old carpets were removed, I noticed many small cracks in the concrete slab floor. I called my home inspector to have a look, and he assured me this is normal for a slab and is not a cause for concern.
What bothers me about the condition of the slab is the possibility of radon gas entering through the cracks. I'm not even sure what radon is but I read that it is dangerous and that a concrete slab is a barrier that prevents radon from entering the building. My fear is that the cracks will expose my family to radon. Does this sound like a serious problem?
A. Slab floors do not prevent radon intrusion because nearly all concrete slabs have cracks. In fact, even when no cracks are visible, there are infinitesimal ones through which radon can enter. That being said, here are the basics regarding radon contamination.
Radon is a radioactive gas that is emitted from the soil in varying amounts, depending on the geological characteristics of the locale. Radon is produced by the atomic decay of uranium, a component of such common rock formations as granite and shale. Its presence is so common that ambient radon levels are omnipresent in the outdoor air throughout the world.
Radon gas does not pose a serious health threat unless it occurs in higher than normal concentrations. When a building is constructed over soil that emits radon gas, high concentrations can occur inside the structure. In buildings with raised foundations, radon gas can escape through the foundation vents, rather than entering rooms within the building. In buildings with slab foundations, radon can enter the rooms directly through cracks in the slab.
The belief that concrete slabs provide protection from radon intrusion is a fallacy because radon particles are submicroscopic in size. Reliance on a slab to screen them out is about as effective as using a chicken wire umbrella to stay dry in a rainstorm. Again, this is because all concrete slabs have cracks, many of which are too small to be observed with the naked eye. From the perspective of a radon particle, slab cracks are as wide as the Grand Canyon.
The only way to know if you have excessive concentrations of radon is to have your home tested. If radon levels exceed acceptable level of 4 picocuries per liter, mitigation can usually be achieved for about $1,000 to $2,500.
Mitigation typically involves the installation of a sheet metal shaft, extending from the roof of your home, down through the concrete slab. A small hole is cut into the floor, usually in a closet or other inconspicuous location, allowing for insertion of the metal duct. An electric fan is then installed in the shaft, where it continues to operate indefinitely. Radon gas has a strong affinity for low pressure areas, and the suction created by the exhaust fan draws radon from the soil beneath the slab, venting it to the exterior of the building.
For those wondering why not just open the windows, the problem there would be what to do in cold winter weather.
• To write to Barry Stone, visit him on the web at www.housedetective.com, or write AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.
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