Radon testing measures the concentration of radon, a colourless, odourless, radioactive gas that occurs naturally as uranium in soil and rock decays. Radon can seep into buildings through cracks in foundations, gaps around pipes, and other openings in contact with the ground. Prolonged exposure to elevated radon levels is the second leading cause of lung cancer after smoking, according to the World Health Organization. Testing is the only way to know whether a property has a radon problem, since the gas cannot be detected by human senses.
How Radon Enters Buildings
Radon migrates from the soil into buildings through the path of least resistance. Common entry points include cracks in concrete slabs, construction joints, gaps around service penetrations, wall cavities in contact with soil, and exposed soil in crawl spaces. The concentration inside a building depends on the uranium content of the local geology, the building's construction type, ventilation rate, and weather conditions.
Testing Methods
Short-term tests, lasting two to seven days, use charcoal canisters or alpha-track detectors placed in the lowest habitable level of the building. Long-term tests, running 90 days or more, provide a more accurate annual average. Continuous radon monitors (CRMs) record hourly readings and are often used by professional inspectors for real estate transactions. Results are measured in becquerels per cubic metre (Bq/m3) or picocuries per litre (pCi/L).
Action Levels
The US EPA recommends mitigation at or above 4 pCi/L (148 Bq/m3), while the WHO suggests a lower reference level of 100 Bq/m3. Many countries have established their own action levels. In areas with known elevated radon, testing is commonly required or strongly recommended as part of a pre-purchase inspection.
Mitigation
If testing reveals elevated levels, a radon mitigation system, typically sub-slab depressurisation, can reduce concentrations by up to 99%.