This glossary explains common radon testing, radon mitigation, crawl space encapsulation, and indoor air quality terms in plain language. For concise machine-readable access, see the Markdown glossary.

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Active soil depressurization

A mitigation method that uses a continuously operating fan and sealed piping to draw radon-containing soil gas from beneath a building and exhaust it safely outdoors. See how radon mitigation works.

Becquerels per cubic meter (Bq/m³)

The SI unit for radon concentration used outside the United States. 1 pCi/L equals 37 Bq/m³, so 4.0 pCi/L is about 148 Bq/m³. See our guide to radon levels and pCi/L.

Closed-house conditions

Test conditions that limit outside-air exchange so a short-term result is meaningful. Exterior doors and windows stay closed except for normal entry and exit, subject to the applicable protocol. See how they apply to radon testing.

Continuous radon monitor

An electronic instrument that records radon readings over time and can help identify unusual test conditions or hourly changes. Read about professional radon testing.

Crawl space encapsulation

Sealing a crawl space with a durable liner over the floor and walls and closing vents so the space is separated from the soil and outside air. See our crawl space encapsulation service.

EPA action level

The U.S. EPA recommends fixing a home when the radon result is 4.0 pCi/L or higher and advises considering action between 2.0 and 4.0 pCi/L. See what a high radon level means.

EPA radon zone

EPA’s county map classification of predicted average indoor radon screening levels: Zone 1 above 4 pCi/L, Zone 2 from 2 to 4 pCi/L, and Zone 3 below 2 pCi/L. A zone does not predict any single home’s level; only a test does. See regional radon risks.

Exhaust stack

The vertical pipe that discharges soil gas outdoors, routed to a discharge point set by the applicable mitigation standard, typically above the roofline and away from windows and other openings. Read about radon mitigation pipe size.

Follow-up radon test

A radon measurement performed after mitigation to measure the resulting concentration. Air Sense Environmental recommends arranging this test separately and confirming the provider, timing, and price in the written estimate; it is not automatically included with installation. Read about post-mitigation radon testing.

Illinois radon license

Illinois requires radon measurement and mitigation professionals to hold a license from the Illinois Emergency Management Agency (IEMA). Licenses can be checked in the IEMA public registry. See what to look for in a licensed radon mitigation contractor.

Indoor air quality

The condition of the air inside a building as it affects occupants, shaped by pollutants such as radon, volatile organic compounds, and particulates, plus humidity and ventilation. See our indoor air quality testing service.

Long-term radon test

A radon test that lasts more than 90 days. It reflects seasonal variation better than a short-term test and gives a closer estimate of the year-round average. Compare how long to test for radon.

Manometer

A small pressure indicator installed on a mitigation system. It shows whether the fan is creating suction; it does not measure the radon level. See how to read a radon manometer.

Passive radon test device

A test that needs no power, such as a charcoal canister, alpha-track detector, or electret ion chamber. It is exposed for a set period and then analyzed by a laboratory. Read whether DIY radon test kits are accurate.

pCi/L

Picocuries per liter, the unit commonly used to report radon concentration in air in the United States. Learn more in our guide to radon levels and pCi/L.

Pressure field extension

The reach of negative pressure beneath a slab from a suction point. Diagnostic testing helps determine whether the proposed system can influence the required foundation area. Learn how a system is installed.

Radon

A naturally occurring radioactive gas produced by the decay of uranium in soil, rock, and water. Radon is invisible, odorless, and tasteless, so testing is the only way to know a building’s level. Learn what radon is and where it comes from.

Radon decay products

Short-lived radioactive particles formed as radon decays, sometimes called radon progeny or radon daughters. They can attach to dust and be inhaled. Learn more about radon gas.

Radon entry points

Openings where soil gas can enter a building: slab cracks, floor-wall joints, sump pits, floor drains, utility penetrations, and exposed soil in crawl spaces. Read about foundation cracks and radon.

Radon fan

A continuously rated fan designed to move soil gas through mitigation piping. Fan selection depends on foundation conditions and diagnostic results. Read about radon fan replacement.

Radon mitigation

Any process that reduces radon concentrations in the occupied areas of a building. In homes this usually means an active soil depressurization system. See our radon mitigation service.

Radon mitigation system

The installed combination of a suction point, sealed piping, a radon fan, an exhaust discharge outdoors, and a system indicator such as a manometer. Learn how a radon mitigation system is installed.

Radon-resistant new construction

Building techniques installed during construction, such as a gas-permeable layer, plastic sheeting, sealing, and a vent pipe, that make it easier to reduce radon later. Read whether radon affects new homes.

Radon testing

Measuring the radon concentration in a building’s air, usually reported in pCi/L, with a passive device or an electronic monitor placed in the lowest lived-in level. See our radon testing service.

Relative humidity

The amount of water vapor in air compared with the most it could hold at that temperature, shown as a percent and measured with a hygrometer. Learn about indoor air quality testing.

Service area

A geographic area where a company performs work. A service area does not by itself represent a staffed physical office. See the Air Sense Environmental service area.

Short-term radon test

A test that typically lasts from 2 to 90 days. Many real-estate and diagnostic tests use a shorter closed-house measurement period. See short-term versus long-term testing and our radon testing service.

Soil gas

The air in the spaces between soil particles. Radon moves into buildings with soil gas, which is why mitigation systems draw soil gas away from the foundation. See how radon mitigation works.

Stack effect

Air movement caused by warm indoor air rising and leaking out of upper levels, which pulls replacement air, and soil gas, in at the lowest level. It is stronger in cold weather. See radon levels in winter versus summer.

Sub-membrane depressurization

A mitigation method for crawl spaces that uses a sealed membrane over exposed soil with suction beneath the membrane. Compare the types of radon mitigation systems.

Sub-slab depressurization

A type of active soil depressurization in which suction is created beneath a concrete slab. See our detailed sub-slab depressurization guide.

Suction point

The location where mitigation piping connects to the space beneath a slab or membrane so a fan can draw out soil gas. See the radon mitigation system diagram.

Sump pit cover

A sealed, airtight lid over a sump pit. It closes a common radon entry point and can let the pit serve as a suction point. See sump pump radon mitigation.

Vapor barrier

A material that resists moisture diffusion. In a crawl space it is the liner laid over exposed soil, and it can double as the membrane for sub-membrane depressurization. Learn about crawl space encapsulation.

Volatile organic compounds (VOCs)

Carbon-based chemicals that evaporate at room temperature from products such as paints, cleaners, and furnishings, and can build up indoors. Learn about indoor air quality testing.

Primary references

These definitions are general information, not property-specific, medical, legal, regulatory, or contractual advice. Have a term you want explained? Contact Air Sense Environmental.

Radon Glossary