After cigarette smoke, radon gas is the second leading cause of lung cancer, causing more than 15,000 deaths each year. Radon-222 is a colorless, odorless gas that forms from the decay of naturally occurring uranium-238. Since U-238 occurs in soil and rock throughout the world, radon gas seeps into homes through the soil. Breathing radon does not cause any short-term health effects such as shortness of breath, coughing, headaches, or fever.
One of 15 homes in the United States has greater than 4 pico curies per liter, a radon level the Environmental Protection Agency considers dangerous. The only way to determine the level is to test. Radon test kits are available in hardware stores and other retail outlets. Many people find it preferable to hire a professional when testing is being conducted as part of a real estate transaction.
Radon levels in a building change from day to day. Highest indoor levels occur in the winter when doors and windows are more likely to be closed. The average cost to install radon-resistant features in an existing home is $800 to $2,500. The average cost to install radon-resistant features in a new home during construction is $350 to $500. See the EPA's Radon Guide and AARST's Radon Resources