Radon is a naturally occurring radioactive gas which originates from the decay of uranium in rocks and soils. It is colourless, odourless and tasteless and can only be measured using special equipment. When radon surfaces in the open air, it is quickly diluted to harmless concentrations, but when it enters an enclosed space, such as a house or other buildings, it can sometimes accumulate to unacceptably high concentrations.
Radon decays to form tiny radioactive particles, some of which remains suspended in the air. When inhaled into the lungs these particles give a radiation dose which may damage cells in the lung and eventually lead to lung cancer.
Technical Guidance Document C of the 1997 Building Regulations, which came into force on the 1st of July 1998, sets out radon preventative measures to be applied in the construction of new dwellings or long stay residential buildings.
It is estimated that more than two thirds of the radiation dose received by the average person in Ireland is due to radon.
Radon from the ground gets into the buildings mainly through cracks in floors or gaps around pipes or cables. As the pressure in a building is slightly lower than the pressure outdoors, radon will be drawn from the ground into the building. This phenomenon is known as a pressure-driven flow.
What is a high radon area:
A high radon area is an area in which more than 10% of the houses are predicted to have indoor radon levels greater than 200 Bq/m3. 

A publication titled "Radon In Existing Buildings" published by the department of environment gives  corrective measures of controlling Radon and also provides information and maps regarding radon in Ireland.

Related Links:
• Radon Specialists In Your Area

Related Downloads:
• Radon In Existing Buildings
  This article published by the dept of environment outlines corrective measures and also has detailed information including maps regarding Radon in Ireland