Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas occurring naturally as the decay process of uranium. It is considered to be a health hazard because of its radioactivity and is responsible for the majority of public exposure to ionizing radiation. According to the United States Environmental Protection Agency Radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21 000 cases of lung cancer deaths per year in the US.
Radon is naturally found in soil and rock and because of its density can build up in basements and confined spaces. To block the release of soil gas (Radon) a sheet of plastic is placed under the basement slab and sealed to all the concrete walls.
Who said old houses are better?
You can see pictures of this vapour barrier in Thursdays Basement Insulation post.