Radon Mitigation

Mitigation is recommended when a long-term measurement (at least 90 days) exceeds the applicable reference level: 300 Bq/m³ in the European Union under Directive 2013/59/Euratom, or 4 pCi/L (≈148 Bq/m³) in the United States according to the EPA. The WHO encourages keeping levels below 100 Bq/m³ where feasible.

There is no threshold below which radon risk is zero — the lower, the better — but these reference levels are the internationally agreed triggers for action.

The most effective and widely used technique is active sub-slab depressurization (ASD): a suction point is created under the building's slab and a fan extracts the radon-laden soil gas through a pipe, releasing it above the roof before it can enter the building. Variants exist for crawl spaces (sub-membrane depressurization) and for buildings on sumps or drainage layers.

Complementary measures include sealing cracks, construction joints and service penetrations; improving ventilation of the occupied space or the underfloor void; and installing radon barriers in new construction. Sealing alone is rarely sufficient, but it improves the performance of active systems.

In new buildings, radon protection is far cheaper to include at the design stage. Many national building codes in radon-prone areas already require a barrier and a standby depressurization provision.

A qualified radon professional starts with a diagnosis: the measured levels, the building's foundation type, and communication tests to locate soil-gas entry routes. The system is then dimensioned, installed and verified with a post-mitigation measurement.

Always verify the result with a new long-term test after installation, and re-test periodically — fans age, buildings are renovated, and usage patterns change.

Several countries maintain registers or certification schemes for radon measurement and mitigation services. Asking for post-mitigation verification measurements and references from previous projects is a reasonable minimum standard everywhere.