New Guidance Clarifies Risks in Zone 1 Radon Area for Home Buyers

Updated recommendations from environmental health authorities are drawing fresh attention to the risks posed by naturally occurring radioactive gas in properties located in a Zone 1 radon area. The designation, used by public health agencies to rank geographical regions by their potential for elevated indoor radon concentrations, places the highest priority on testing and mitigation in these zones. The new guidance aims to clarify the obligations of sellers, landlords, and real estate professionals when marketing or transferring properties in areas where radon levels are most likely to exceed safety thresholds.

Radon is a colourless, odourless gas that forms from the natural decay of uranium in soil, rock, and water. It can enter buildings through cracks in foundations, gaps around service pipes, and other openings in the floor or walls. Long-term exposure to elevated concentrations is the second leading cause of lung cancer after smoking, according to health protection agencies. The classification system that defines a Zone 1 radon area is based on geological surveys, indoor radon measurements, and predictive mapping. Homes in these zones are statistically more likely to have indoor radon levels above the action limit of 200 becquerels per cubic metre, the point at which mitigation is strongly advised.

What the Zone 1 Designation Means for Property Transactions

The new guidance clarifies that a property located in a Zone 1 radon area does not automatically have unsafe radon levels. The zone classification reflects the potential for elevated concentrations, not a guarantee that any given building will exceed the threshold. However, the guidance strongly recommends that buyers and sellers treat the zone designation as a trigger for testing. A short-term radon test, typically lasting between three and 12 months depending on the device and protocol, provides the only reliable way to determine whether a specific property requires remedial work.

Real estate professionals are being advised to disclose the zone status to prospective purchasers early in the transaction process. In some jurisdictions, disclosure of known radon risks is already a legal requirement, but the new guidance goes further by suggesting that the absence of a test result should not be taken as evidence of safety. For properties in a Zone 1 radon area, the recommended course of action is to test before closing or to negotiate a contingency that allows for testing and subsequent mitigation. Sellers who have already completed radon mitigation are encouraged to provide documentation of the work, including the post-mitigation test results, to assure buyers that the risk has been addressed effectively.

Mitigation Options and Costs

When testing confirms radon levels above the action limit, a range of mitigation techniques can reduce concentrations. The most common method is sub-slab depressurization, which involves installing a vent pipe and fan system that draws radon from beneath the building and exhausts it safely outdoors. Other approaches include sealing major entry routes, improving ventilation in basements and crawl spaces, and installing heat recovery ventilators that dilute indoor air without excessive energy loss. The cost of mitigation varies depending on the construction type, the severity of the problem, and the chosen technique, but it is generally far lower than the health and economic costs of ignoring the issue.

The new guidance emphasises that mitigation should always be carried out by a certified radon professional. Improper installation can leave gaps in the soil gas barrier or create negative pressure that draws more radon into the living space. After mitigation, a follow-up test is essential to confirm that concentrations have fallen below the action limit. Homeowners in a Zone 1 radon area who have already mitigated are advised to retest every two years, as changes in the building envelope or ground conditions can alter radon entry rates over time.

Implications for New Construction

Building codes in regions that include a Zone 1 radon area are increasingly mandating radon-resistant construction techniques for new homes. These measures typically include a layer of gas-permeable aggregate beneath the foundation, a polyethylene vapour barrier, sealed joints around pipes and wiring penetrations, and a passive vent stack that can be activated with a fan if post-construction testing shows elevated levels. The cost of incorporating these features during construction is modest compared with retrofitting an existing home. The new guidance encourages builders and developers to view these requirements not as optional extras but as standard practice in high-risk zones.

Local authorities are also being urged to make radon testing a routine part of building inspection and occupancy permitting. In areas where testing rates have historically been low, the new guidance could lead to a significant increase in the number of homes that are tested and, where necessary, remediated. Public health campaigns are being planned to raise awareness among homeowners, many of whom remain unaware that their property sits in a Zone 1 radon area or that free or low-cost test kits are available through regional health units.

Health Risks and Long-Term Exposure

The health risks associated with radon are cumulative. The likelihood of developing lung cancer increases with both the concentration of radon and the duration of exposure. For a person living in a home with radon levels above the action limit for many years, the individual risk can approach that of smoking a pack of cigarettes a day, depending on the concentration. Smokers and former smokers face a compounded risk, as the combination of tobacco smoke and radon decay products dramatically increases the probability of cellular damage in the lungs.

The new guidance includes updated risk estimates based on recent epidemiological studies and improved models of radon decay product behaviour. These estimates reinforce the message that no level of radon is entirely safe, though the risk at concentrations below the action limit is much lower. For residents of a Zone 1 radon area, the most effective single step to reduce health risk is to test the home and, if necessary, mitigate. Public health authorities stress that the gas is undetectable by human senses, which makes testing the only way to know whether a problem exists.

Looking Ahead: Policy and Public Awareness

The updated guidance is part of a broader effort to standardise radon risk communication across jurisdictions. In the past, inconsistencies in how zones were defined and communicated led to confusion among homeowners and real estate professionals. The new framework aims to make the classification more transparent and actionable. For anyone involved in buying, selling, or renting a property in a Zone 1 radon area, the message is clear: test the home, mitigate if needed, and keep records of the results.

Public health agencies are also exploring ways to integrate radon risk information into property listings, mortgage applications, and home insurance policies. While these measures are still under discussion, they reflect a growing recognition that radon exposure is a preventable health hazard that requires coordinated action by homeowners, industry, and government. The new guidance provides a practical starting point for that action, with a focus on testing and mitigation rather than alarm.

For homeowners who have not yet tested, the process is straightforward. Test kits are available from local health authorities, online retailers, and some hardware stores. The kits are placed in the lowest lived-in level of the home for a period of three to 12 months, then sent to a laboratory for analysis. Results are typically available within two weeks. If the result shows a concentration above 200 becquerels per cubic metre, the homeowner should contact a certified radon mitigation professional. For those in a Zone 1 radon area, the guidance recommends testing without delay, as the potential for elevated levels is highest in these locations.