Radon is a naturally occurring radioactive gas, invisible and odorless, which can seep into homes located on certain types of soil. If you are selling a property in an area with significant radon potential, a specific information requirement applies during the transaction. This article reviews the regulations, health risks, and practical solutions to reassure your buyers.
In Summary
- Radon is a naturally occurring radioactive gas resulting from the decay of uranium present in certain soils, particularly granite and volcanic soils.
- France is divided into three radon potential zones; in zone 3, the seller must inform the buyer through the risk assessment report, but no technical measurement is mandatory for the sale.
- The reference level for indoor air is set at 300 Bq/m³; above this level, corrective measures are recommended, and potentially a building assessment if the exceedance persists.
- Simple solutions (ventilation, sealing floors and walls in contact with the ground, extraction) can most often effectively reduce radon concentrations.
What Is Radon and What Are the Health Risks?
A Naturally Occurring Radioactive Gas That Cannot Be Detected Without Measuring Equipment
Radon is a naturally occurring radioactive gas, colorless and odorless, resulting from the decay of uranium present in the Earth's crust. It is particularly prevalent in granite and volcanic soils, which explains its very uneven distribution across French territory. Coming from the ground, it can seep into buildings through foundation cracks, pipe joints, or poorly sealed floors, and accumulate in enclosed, poorly ventilated spaces, particularly cellars, basements, and ground floors.
The Second Leading Cause of Lung Cancer After Smoking
According to health authorities, radon is considered the second leading cause of lung cancer in France, after smoking. The risk results from prolonged exposure to high concentrations, particularly in confined and inadequately ventilated homes. This risk does not appear immediately: it is cumulative exposure over several years that poses a problem, hence the importance of taking action in advance, particularly when selling a property.
Radon Potential Zoning in France
Three Zones Defined by Order
French municipalities are classified into three categories of radon potential zones, based on the geological characteristics of the soil. Zone 1 corresponds to low radon potential, zone 2 to low potential but with specific geological factors that may promote the transfer of gas into buildings, and zone 3 to significant radon potential. This zoning was established by order, and the list of municipalities concerned can be consulted in particular on the Géorisques platform.
How to Find Out Your Municipality's Zone
Before putting a property up for sale, it is useful to check the classification of your municipality on Géorisques, which lists all radon potential zones. If you are in zone 3, your local Capifrance real estate advisor can assist you in correctly incorporating this information into your sales file and anticipating buyers' questions.
Information Requirements When Selling a Property
A Mandatory Statement in the Risk Assessment Report in Zone 3
When a property located in a municipality classified as zone 3 is put up for sale, the seller is required to inform the buyer of the radon risk. This information is included in the risk and pollution assessment report (ERP), a document that must be attached to any preliminary sale agreement or deed of sale. It recalls the nature of the risk and invites the buyer to find out more about the subject.
An Information Requirement, Not a Measurement Requirement
It is important to clarify this point: unlike other property assessments, there is no legal requirement to have a radon level measurement carried out before a sale. The regulations impose an obligation to provide information about the risk through the risk assessment report, but not a mandatory technical measurement assessment for the transaction itself. A seller may nevertheless choose to have a measurement carried out voluntarily, which can reassure the buyer and facilitate negotiations.
How to Measure Radon Levels in a Home
The Dosimeter, the Reference Tool
Radon measurement is primarily based on the use of dosimeters, small passive sensors placed in living areas, particularly those in contact with the ground. These dosimeters must remain in place for several weeks, ideally during the heating season, in order to take into account variations in concentration related to ventilation and weather conditions.
Using a Professional or a Test Kit
The measurement can be carried out by a professional property assessor, who places the dosimeters, collects them after the recommended period, and provides the results together with a laboratory analysis. Measurement kits are also available to the general public; they are less precise than professional testing but useful for an initial assessment. In case of doubt or a high result, it is recommended to confirm the measurement with the help of a professional.
Reference Levels and Recommended Actions
The 300 Bq/m³ Threshold
The reference level for radon concentration in indoor air is set at 300 becquerels per cubic meter (Bq/m³). Below this threshold, the risk is considered limited, although there is no strictly risk-free threshold, as radon is a cumulative risk factor.
What to Do in the Event of an Exceedance
When the measured concentration exceeds 300 Bq/m³, simple corrective measures, such as improving ventilation, most often make it possible to bring the level back to a satisfactory level. If the concentration remains high after these common-sense measures, or if it significantly exceeds the reference level, it is recommended to have the building assessed by a professional in order to identify the gas entry routes and propose suitable work.
Solutions for Reducing Radon Concentration in a Home
Improve Ventilation
The first measure, and often the most effective, is to improve indoor air renewal: regularly airing rooms, maintaining or installing a mechanical ventilation system (VMC), particularly in basements and crawl spaces. Good ventilation limits gas accumulation by continuously diluting it.
Improve the Sealing of Floors and Walls
Radon mainly enters through cracks, floor slab joints, and pipe penetration points. Treating these leakage points, particularly in floors and walls in contact with the ground, significantly reduces the entry of gas into the building.
Install an Extraction System
In the most significant cases, an extraction system or soil depressurization system beneath the slab (often referred to as radon extraction) can be installed to capture the gas before it enters occupied spaces and discharge it outside. This more technical solution is generally implemented after a building assessment.
Practical Advice for a Seller Located in a Radon Potential Zone
If your property is located in zone 3, anticipate checking your municipality's classification on Géorisques as soon as you prepare your sales file, so that you can incorporate this information calmly into the risk assessment report. Having a voluntary radon level measurement carried out, even though it is not mandatory, can be an argument for transparency and trust with buyers. If reduction work has already been carried out, mention it and keep the supporting documents, as they add value to your property. Finally, to secure every stage of your project, from preparing the file through to signing, the assistance of a local Capifrance real estate advisor remains valuable, as does a free property valuation to position your property on the market before putting it up for sale.
Conclusion
Radon is a well-identified natural risk, governed by clear regulations: mandatory information in the risk assessment report for properties located in zone 3, without a systematic requirement for technical measurement when selling. By finding out about your municipality's zoning, considering a voluntary measurement, and knowing the corrective solutions available, you can approach the sale of your property with peace of mind. To refine your sales strategy and discover comparable properties, do not hesitate to consult our property listings or speak with a local advisor.
FAQ
Is a Radon Assessment Mandatory When Selling a Property?
No, there is no legal requirement to measure radon levels when selling a property. However, in municipalities classified as zone 3, the seller must inform the buyer of the radon risk through the risk and pollution assessment report (ERP), which must be attached to the preliminary sale agreement or deed of sale.
How Can I Find Out Whether My Municipality Is Classified as a Radon Potential Zone?
The classification of each French municipality in zone 1, 2, or 3 can be consulted free of charge on the Géorisques platform. Simply enter the address or name of the municipality to find out its level of radon potential.
What Is the Radon Concentration Threshold That Should Not Be Exceeded?
The reference level for indoor air is set at 300 Bq/m³. Below this threshold, the risk is considered limited; above it, corrective measures are recommended, and a building assessment may prove necessary in the event of a persistent exceedance.
How Long Does It Take to Measure Radon Levels in a Home?
The measurement is based on dosimeters that must remain in place for several weeks, ideally during the heating season, to provide a reliable estimate of annual exposure. A measurement that is too short does not make it possible to take seasonal variations in concentration into account.
What Solutions Are Available if Radon Levels Are Too High?
The most common solutions consist of improving ventilation in the home, strengthening the sealing of floors and walls in contact with the ground, and, in more significant cases, installing an extraction system beneath the slab. These measures most often make it possible to bring the concentration below the reference level.
Can Radon Risk Reduce the Sale Price of a Property?
Classification in zone 3 does not prevent a sale and does not automatically reduce the value of a property, provided that the information is properly communicated and that any corrective measures are mentioned. A free property valuation carried out by a professional makes it possible to accurately determine the value of your property while taking all of its characteristics into account.
Author
Frédéric Rémy – Director of Sales Performance
A real estate professional with several years of experience within the Capifrance network, I would like to share essential advice with you to help you successfully complete your property project with our advisors.
