Radon gas is, according to the World Health Organization, the leading cause of lung cancer among non-smokers and the second among smokers, after tobacco. Despite its public health significance, it remains a contaminant largely unknown to the general public, partly because it is impossible to detect without specific instrumentation: it is colorless, odorless, and non-irritating.
At Litoclean we work in the research, diagnosis, and remediation of soils and subsoils, areas directly related to radon behavior in the ground. Understanding the origin of this gas, the mechanisms by which it enters buildings, and the measures available to control its concentration is essential for both industry professionals and property owners located in risk zones.
What is radon gas?
Radon (Rn-222) is a naturally occurring radioactive gas generated as a product of the decay of radium-226, which is itself part of the uranium-238 decay chain. These elements occur naturally in the Earth’s crust, although their concentration varies significantly depending on the type of rock and soil.
As a noble gas, radon is chemically inert and has a high capacity to migrate through the pores and fissures of the ground. Its half-life is 3.8 days, during which time it can travel considerable distances before decaying and generating alpha radioactive particles — known as “radon daughters” — which represent the real health risk when inhaled.
How does radon originate in the subsoil?
Radon production is linked to the presence of uranium and radium in geological formations. The soils and rocks with the greatest radon generation potential are:
- Granitic igneous rocks: granites are particularly rich in uranium and constitute the areas with the highest radon emissions in the Iberian Peninsula, particularly in Galicia, western Castile and León, Extremadura, and the Central Mountain System.
- Metamorphic rocks: slates, schists, and gneisses can contain significant concentrations of uranium, depending on their original parent rock.
- Derived soils and sediments: materials from the erosion of granitic and metamorphic rocks retain part of their uranium content, making residual and alluvial soils in these areas potential emitters.
- Associated aquifers: groundwater in contact with uranium-rich formations can dissolve radon and transport it over significant distances. Consuming well or spring water without adequate aeration can represent an additional exposure pathway.
Once generated, radon moves toward the surface through the pores, fractures, and discontinuities of the ground. In open spaces it quickly dilutes in the atmosphere and does not represent an appreciable risk. The problem arises when the gas reaches enclosed and poorly ventilated spaces, such as building interiors, where it tends to accumulate.
Radon gas and lung cancer: the scientific evidence
The relationship between radon exposure and the development of lung cancer is supported by decades of epidemiological research. The most relevant studies include:
- Research carried out in uranium mines during the second half of the 20th century, which demonstrated a significant increase in the incidence of lung cancer among exposed miners.
- The European collaborative study published by Darby et al. (2005), which demonstrated a 16% increase in lung cancer risk for every 100 Bq/m³ increase in mean residential radon concentration.
- The WHO (2009) and International Agency for Research on Cancer (IARC) reports, which classify radon as a Group 1 carcinogen.
When air containing radon is inhaled, alpha particles emitted by its decay products impact directly on the bronchial epithelium, causing damage to cellular DNA. This mechanism is cumulative: the higher the concentration and the longer the exposure, the greater the risk. The interaction with tobacco has a multiplying effect, which is why radon represents a particularly high risk for smokers.
How does radon enter buildings?
Since radon comes from the subsoil, the highest concentrations within a building are found on the lower floors: basements, semi-basements, and ground floors. Being denser than air, the gas tends to remain in the lowest areas of the building.
The main entry routes for radon into buildings are:
- Cracks and fissures in the floor slab and walls in contact with the ground.
- Construction joints between the floor slab and the perimeter wall.
- Service penetrations (pipes, electrical conduits) passing through the crawl space floor.
- Building materials with high radium content (uncommon in Spain).
- Supply water from underground sources containing dissolved radon.
The pressure difference between the building interior and the ground — generated by heating and ventilation systems and the “chimney effect” — promotes the suction of gas from the subsoil into the interior. Buildings with poor airtightness in the envelope in contact with the ground are therefore particularly vulnerable.
Applicable regulations: the Spanish Technical Building Code
In Spain, the main regulatory reference is the amendment to the Technical Building Code (CTE), approved by Royal Decree 732/2019, which incorporates section HS 6 “Protection against radon exposure” into the Basic Health Document. This amendment partially transposes Council Directive 2013/59/Euratom.
The CTE establishes a reference level of 300 Bq/m³ for radon concentration inside buildings and classifies the national territory into zones according to the radon potential of the soil:
- Zone I: municipalities with values between 1 and 2 times the reference level. Basic protective measures are required (ground barrier).
- Zone II: municipalities with values exceeding 2 times the reference level. Additional protective measures are required (barrier + depressurization system or specific ventilation).
The requirements apply to new construction, changes of use, renovations, and extensions affecting habitable spaces in contact with the ground. It is important to note that the WHO recommends a more stringent reference level of 100 Bq/m³, and that several European countries have already adopted values lower than the Spanish standard.
How is radon measured? Diagnostic campaigns
Measuring radon is the essential first step to assessing the actual situation of a property. Two main approaches are distinguished:
Short-term measurements
These provide instantaneous concentration values using portable electronic devices. They are useful for a quick initial assessment or for identifying the main radon entry routes into a building. However, they are not representative of the average annual exposure, as radon concentrations fluctuate significantly depending on ventilation, outdoor temperature, and seasonality.
Long-term integrated measurements
These constitute the reference method for assessing average annual concentration. Passive track-etch detectors (CR-39 type or similar) are used, placed for a minimum period of three months — ideally between six months and one year — in regularly used rooms on the ground floor or basement. The detectors are subsequently sent to an accredited laboratory for analysis.
Additionally, continuous monitoring devices are available that record the temporal evolution of radon concentration at short intervals (hourly or daily), providing detailed information on gas accumulation patterns and their response to ventilation.
Solutions to mitigate radon in buildings
The range of measures available to reduce radon concentration inside buildings includes both interventions on existing buildings and preventive measures for new construction.
Measures in existing buildings
- Sub-slab depressurization systems (SDS): these involve installing an extraction point beneath the floor slab connected to a fan that creates negative pressure in the ground below the building. This is the most effective technique, capable of reducing radon concentration by between 50% and 99%, depending on ground conditions and quality of installation.
- Improved ventilation: increasing the air renewal rate on lower floors through natural or mechanical ventilation dilutes radon concentration. It is a simple measure but less effective than depressurization systems, especially in cold climates where continuous ventilation entails an energy penalty.
- Sealing entry routes: waterproofing cracks, joints, and service penetrations reduces the volume of radon entering the building. Although rarely sufficient on its own, it significantly improves the effectiveness of other measures.
- Pressurization of the living space: by injecting outdoor air, the indoor pressure is made higher than that of the ground, reversing the gradient that favors radon ingress. This is applicable in buildings with good airtightness.
Preventive measures in new construction
- Radon barrier: a gas-impermeable membrane installed between the floor slab and the ground, with sealed overlaps and continuity at wall junctions.
- Ventilated air gap: a crawl space or ventilated void that allows natural or forced ventilation of the space between the ground and the habitable floor, diluting radon before it reaches the interior.
- Pre-installed depressurization system: installation of ducts and the extraction point during construction, without activating the fan, so that the system can be activated if subsequent measurements reveal elevated concentrations.
The selection of the appropriate solution depends on the specific diagnosis of each building: measured concentration level, type of foundation, geological ground conditions, intended use of the property, and the constructive feasibility of each alternative. A professional diagnosis prior to any intervention is therefore essential.
Litoclean’s role in radon management
At Litoclean we have more than two decades of experience in the investigation and characterization of soils and subsoils. Our knowledge of geology, hydrogeology, and gas behavior in the ground allows us to approach radon-related challenges with a comprehensive methodology:
- Preliminary assessment of potential radon risk based on the geological information of the site.
- Design and execution of measurement campaigns tailored to each scenario (residential buildings, public buildings, workplaces).
- Interpretation of results and proposal of mitigation or prevention measures, in accordance with current regulations.
- Technical advisory services to developers, architects, and public administrations on the application of CTE HS 6.
If you need to assess the presence of radon gas in a property or site, contact our team. We will help you identify the situation and propose the most appropriate solutions.
Frequently asked questions about radon gas
What is radon gas and where is it found?
Radon gas is a naturally occurring radioactive gas produced by the decay of uranium present in rocks and soils. It is found throughout the world, although its concentration is higher in areas with granitic, slate, and metamorphic substrates. In Spain, the regions with the highest presence are Galicia, western Castile and León, Extremadura, and parts of the Central Mountain System.
How is radon gas produced?
Radon is continuously generated in the subsoil as a result of the radioactive decay chain of uranium-238: uranium transforms into radium-226, which in turn decays into radon-222. Being a gas, it migrates through pores and fissures in the ground toward the surface.
What is the relationship between radon gas and lung cancer?
Prolonged inhalation of radon and its decay products causes irradiation of the bronchial epithelium, increasing the risk of developing lung cancer. According to the WHO, radon is the leading cause of lung cancer among non-smokers and is responsible for between 3% and 14% of all cases, depending on the country.
What is the radon level considered dangerous?
The CTE establishes a reference level of 300 Bq/m³ for radon inside buildings in Spain. The WHO recommends a more stringent level of 100 Bq/m³. Above 300 Bq/m³, regulations require corrective measures in existing buildings or preventive measures in new construction.
The CTE classification assigns a prior risk level and requires the application of measures (basic in Zone I and additional in Zone II) for new construction, changes of use, and renovations, even if no measurements have been carried out.
Measurement serves to verify the actual concentration, assess effective exposure, and justify, where appropriate, adjustments or exceptions to the constructive solutions applied or required under the regulations.
How can I find out if my home has radon?
The only way to determine the radon concentration in a home is through a specific measurement. It is recommended to place passive detectors for a minimum of three months on the lowest inhabited floor. For a professional diagnosis, it is advisable to engage the assistance of specialist companies such as Litoclean.
Can radon be completely eliminated from a building?
It is not possible to eliminate radon emissions from the ground, but it is possible to reduce its concentration inside the building to safe levels. Sub-slab depressurization systems achieve reduction efficiencies of between 50% and 99%. The key is an adequate diagnosis and the selection of the appropriate technical solution for each case.
