Glossary
Radon terms, in plain language
From becquerels to weeping tile: 35 terms you’ll meet in test reports, quotes and building code documents.
Active soil depressurization (ASD)
- The standard radon mitigation method in Canada. A fan and pipe keep the soil beneath a building at lower pressure than the indoor air, so radon is drawn out and vented outside instead of entering. Also called sub-slab depressurization. Learn more
Alpha particle
- A type of radiation released by radon and its decay products. It travels only a short distance but can damage lung cells when decay products are inhaled.
Alpha-track detector
- A small passive device used for long-term radon tests. Alpha particles leave microscopic tracks on a plastic film that a lab counts to calculate the average radon concentration.
Becquerel (Bq)
- The SI unit of radioactivity: one radioactive decay per second.
Bq/m³
- Becquerels per cubic metre, the unit Canada uses for radon in air. 200 Bq/m³ means 200 radioactive decays per second in each cubic metre of air.
C-NRPP
- The Canadian National Radon Proficiency Program, which certifies radon measurement and mitigation professionals and lists approved devices and labs. Health Canada recommends using C-NRPP certified professionals. Learn more
CAN/CGSB-149.12
- The Canadian standard for radon mitigation options in existing buildings. It sets out how active soil depressurization and other systems should be designed and installed.
Communication test
- A pre-mitigation test that measures how far suction spreads beneath a slab from a test hole. It tells the installer how many suction points and what size fan a system needs. Also called a pressure-field extension test.
Decay products (progeny)
- The short-lived radioactive particles, mainly polonium isotopes, that radon breaks down into. They attach to dust, are inhaled and deliver most of the radiation dose to the lungs.
Digital radon monitor
- An electronic device that displays radon readings continuously. Useful for screening and watching trends; Health Canada recommends confirming decisions with a long-term test.
Early reading
- A two-week result from a calibrated professional continuous monitor placed alongside a long-term detector. Reliable when far above or below 200 Bq/m³; the 91-day result is still the one to decide on. Learn more
Electret ion chamber
- A professional radon detector that measures the drop in charge on an electret over time. It can be used for short- or long-term measurements.
Half-life
- The time it takes for half of a radioactive substance to decay. Radon-222’s half-life is about 3.8 days.
Health Canada radon guideline
- Canada’s recommended action level for radon in homes: an average annual concentration of 200 Bq/m³ in a normal occupancy area. Reduce within 2 years for 200–600 Bq/m³ and within 1 year above 600 Bq/m³. Learn more
Long-term test
- A radon measurement lasting at least 91 days (three months). Health Canada’s guideline is based on long-term results. Learn more
Lowest lived-in level
- The lowest floor of a home where someone spends more than four hours a day. This is where Health Canada recommends placing a radon detector.
Manometer
- A simple U-tube pressure gauge installed on a radon system’s pipe. Uneven fluid levels show the fan is creating suction; level fluid means the system needs attention.
Normal occupancy area
- Any part of a home where someone is likely to spend more than four hours a day. Health Canada’s guideline applies to these areas.
pCi/L
- Picocuries per litre, the U.S. unit for radon in air. 1 pCi/L = 37 Bq/m³. The U.S. EPA action level of 4 pCi/L is about 148 Bq/m³. Learn more
Post-mitigation test
- A radon test after a mitigation system is installed, to confirm it worked. Typically a short check after at least a day of operation, then a long-term test.
Radium
- A radioactive element in the uranium decay chain. Radium in soil and rock decays directly into radon gas.
Radon
- A colourless, odourless, radioactive gas formed by the natural decay of uranium in soil and rock. Long-term exposure is the leading cause of lung cancer in non-smokers. Learn more
Radon rough-in
- Provisions built into a new home so an active radon system can be added later: typically a gas-permeable layer under the slab and a capped, labelled pipe. Required for Part 9 homes under the 2024 Ontario Building Code. Learn more
Short-term test
- A radon test lasting from 2 to 90 days. Useful as a screen, especially in real estate, but not a substitute for a long-term test.
Soil gas
- The air in the spaces between soil particles. It can carry radon, moisture and other gases into buildings.
Soil gas barrier
- A continuous, sealed layer, commonly polyethylene under a slab, that limits soil gas entry into a building. Required in new Ontario homes.
Stack effect
- Warm air rising and escaping from the upper part of a heated building, which lowers pressure at the bottom and draws air (and soil gas) in through the foundation. The main reason radon levels peak in winter. Learn more
Sub-membrane depressurization
- Radon mitigation for crawlspaces and earth floors: a sealed membrane is laid over the soil and suction is applied beneath it.
Suction point
- Where a radon system’s pipe meets the soil or gravel under the slab, usually a small excavated pit beneath a 4–5 inch hole.
Sump
- A pit in the basement floor that collects groundwater from weeping tile. An open sump is a common radon entry point and is sealed with an airtight lid during mitigation.
Tarion
- Ontario’s new home warranty administrator. The builder’s warranty includes radon remediation, up to $50,000, for seven years from possession when long-term tests exceed 200 Bq/m³.
Thoron
- Radon-220, a short-lived radon isotope from the thorium decay chain. Its very short half-life means it usually contributes much less to indoor exposure than radon-222.
Uranium
- A naturally occurring radioactive element found in small amounts in almost all soil and rock. It is the original source of radon.
Weeping tile
- Perforated drain pipe around a foundation footing that carries water to a sump or storm drain. It can also collect soil gas and is sometimes used as part of a mitigation system.
WHO reference level
- The World Health Organization’s recommended reference level for indoor radon: 100 Bq/m³, or no more than 300 Bq/m³ where 100 cannot be achieved.
Know your number in one heating season.
Book a radon test with a C-NRPP certified technician: an early reading at 2 weeks, the full result at 91 days. If it’s high, we’ll design a fix and prove it worked.