New Guidance Details Mitigation for High Radon in Residential Buildings

Updated technical guidance on mitigation for high radon in homes and workplaces has been released, giving property owners and contractors a clearer framework for addressing elevated indoor radon concentrations. The guidance consolidates current measurement protocols, diagnostic procedures, and remediation strategies that can be applied across a range of building types. It arrives at a time when awareness of indoor air quality risks continues to rise, and when regulatory bodies in several regions are tightening reference levels for radon exposure.

Radon is a naturally occurring radioactive gas that seeps from soil into buildings. It is the second leading cause of lung cancer after smoking, according to public health agencies. Because radon is invisible and odourless, the only way to know whether a building has a problem is to test. The new guidance document is designed to help those who find test results above the recommended action level understand what steps to take next. It covers both active and passive approaches to mitigation for high radon, with an emphasis on matching the intervention to the specific building characteristics and the severity of the problem.

What the guidance covers

The document is structured around three main phases: assessment, diagnosis, and remediation. In the assessment phase, the guidance recommends short-term and long-term testing methods and explains how to interpret results in relation to national and international reference levels. It stresses that a single test is not enough; seasonal variations and building use patterns mean that repeated measurements over several months provide a more reliable picture.

Diagnosis involves identifying the primary entry routes for radon. Common pathways include cracks in concrete slabs, gaps around service pipes, floor-wall joints, and openings in suspended floors. The guidance describes inspection techniques and diagnostic tools, such as continuous radon monitors and smoke tests, that help pinpoint where soil gas is entering the building envelope. Without a proper diagnosis, remediation efforts can be misdirected and may not achieve the required reduction.

Remediation strategies

Once the entry points and the driving forces are understood, the guidance sets out a range of remediation options. Passive systems, such as sub-slab depressurisation with a passive stack vent, are often the first choice for new construction. For existing buildings, active soil depressurisation is the most widely used technique. A fan draws soil gas from beneath the slab and exhausts it above the roofline, preventing it from entering the living space. The guidance provides sizing and installation recommendations, including where to locate the fan and how to seal the system to maintain negative pressure.

Other techniques covered include sealing major entry routes, improving ventilation rates, and installing heat recovery ventilators that can maintain energy efficiency while increasing air exchange. The document also addresses mitigation for high radon in buildings with crawl spaces, basements, and slab-on-grade foundations. Each building type presents unique challenges, and the guidance offers decision trees to help contractors choose the most effective and cost-efficient approach.

Who this is for

The primary audience includes radon measurement professionals, home inspectors, building contractors, and health department staff. However, the guidance is written in plain language so that homeowners who want to understand their options can follow the main points. It does not prescribe a single solution because radon levels vary widely by region and by individual site. Instead, it equips the reader with the knowledge to ask informed questions and to evaluate contractor proposals.

Real estate professionals and home buyers also have a stake in this topic. Radon testing is increasingly a standard part of home inspections in areas with known radon potential. Knowing that a reliable mitigation framework exists can make the difference between a deal falling through and a successful sale where the buyer and seller agree on a remediation plan.

Regional differences and building codes

The guidance acknowledges that building codes and radon reference levels differ by jurisdiction. Some areas require radon-resistant construction in new homes, while others leave mitigation to the discretion of the owner. The document does not replace local codes but provides a technical baseline that can be adapted to local requirements. It also notes that mitigation for high radon should not compromise other aspects of building performance, such as moisture control or energy efficiency. A poorly designed mitigation system can create new problems, including increased humidity or back-drafting of combustion appliances. The guidance includes cross-references to standards for ventilation and combustion safety.

Contractors who follow the guidance can expect to produce more consistent results, and homeowners can have greater confidence that the work performed will be effective. The document also includes a section on post-mitigation testing to verify that radon levels have been reduced to below the action level. This verification step is critical because a system that is installed incorrectly or that degrades over time may not provide the expected protection.

Implications for public health

Public health authorities have long promoted testing and mitigation as the most effective ways to reduce radon-related lung cancer risk. Yet uptake remains low. One barrier has been the lack of clear, actionable guidance for homeowners and contractors. The new document aims to lower that barrier by providing a single authoritative reference. If widely adopted, it could lead to a measurable reduction in indoor radon exposure across the housing stock.

Research shows that effective mitigation can reduce indoor radon concentrations by 80 percent or more in most homes, depending on the system and the initial levels. Over time, that translates into a significant reduction in population risk. The guidance is expected to be updated periodically as new materials and techniques become available and as more data on the long-term performance of mitigation systems is collected.

Practical steps for homeowners

For homeowners who have tested and found elevated radon, the first step is to confirm the result with a second test. If levels remain above the action level, the next step is to contact a qualified radon mitigation contractor. The guidance advises asking for a written proposal that includes a diagnostic assessment, a description of the proposed system, and a commitment to post-mitigation testing. It also recommends checking that the contractor follows the procedures outlined in the guidance, as this is a sign of professionalism and technical competence.

Costs for mitigation vary widely depending on the complexity of the installation. Simple passive systems in new construction can be relatively inexpensive, while retrofitting an active system in an existing home may require a larger investment. However, the health benefits and the potential increase in property value often justify the expense. Some regions offer financial assistance or low-interest loans for radon mitigation, and the guidance encourages homeowners to explore these options.

The release of this guidance is part of a broader effort to standardise radon mitigation practices across the industry. It is expected that professional certification bodies will incorporate the guidance into their training programmes, and that building code committees will refer to it when updating radon-resistant construction requirements. As awareness of indoor air quality continues to grow, documents like this one play an essential role in translating scientific knowledge into practical, real-world action.