Radon in dwellings in Germany

From the subsoil, radon enters a building and accumulates there. A small part of it also enters buildings from building materials and from drinking and process water. When inside a building, it can cause lung cancer.

The gas can propagate into all rooms. Generally, its concentration is highest in the basement and on the ground floor. On higher floors, the radon concentration generally reduces because the radon entering from the building subsoil mixes with radon-poor outdoor air.

Measurement values and prognoses

The indoor radon concentration levels are very different. The annual mean value which people are exposed to in living spaces in Germany averages around 65 becquerel per cubic metre. New projections showed that in Germany

• about 10.5 million people are exposed to a radon concentration in the dwelling of more than 100 becquerel per cubic metre and
• of which almost 2 million people are even exposed to a radon concentration above the reference value of 300 becquerel per cubic metre.

Radon concentrations of more than 1,000 becquerel per cubic metre are also possible, but rarely occur.

For every 100 becquerel per cubic meter of long-term radon concentration in the room air, the risk of lung cancer increases by around 16%. There is no indication of a threshold below which radon would be harmless. Therefore, the indoor radon concentration should be reduced as far as this can be achieved with reasonable effort.

Radon concentrations indoors in an individual building cannot be accurately predicted. They can only be determined through measurements.

"Radon Concentrations in Dwellings" map

Estimated average radon activity concentrations (arithmetic mean) of indoor air to which residents of a municipality are exposed in their homes.

The map shows the estimated average radon concentration in indoor air to which people in cities and municipalities are exposed in their living spaces (as off 2022). The map clearly illustrates the extent to which the values vary from region to region.

The different average radon concentrations shown in the map depend not only on the radon concentration in the building ground, but also on the residential structure: In densely populated urban areas, the proportion of multi-family houses and high-rise apartment buildings is greater than in rural areas, where single-family houses dominate. Because of these differences in settlement structure,

• in rural areas, more people live in low floors, which are generally more exposed to radon due to their proximity to the ground, and
• in urban areas, more people live in higher storeys, which are generally less at risk of radon exposure due to their distance from the building ground.

This difference can be clearly seen in the map: Cities such as Berlin, Hamburg, Leipzig, Erfurt, Regensburg or Kassel have significantly lower estimated radon levels than their surrounding areas (which often have a similar radon risk due to geogenic factors).

Estimation based on measurement data and characteristics of the natural environment and buildings

The estimation of the average radon concentrations shown in the map is based on measurement data from the study "Radon in Dwellings" conducted on behalf of the BfS. These measurement data are particularly suitable for this purpose, because the underlying measurements

• were spatially distributed over the federal territory in proportion to the population density,
• ran over a full calendar year,
• took place uniformly in the period 2019-2020,
• were adhered to a uniform measurement protocol (detector type, detector evaluation, etc.), and
• were specified by surveying the floor, year of construction and building type.

In addition to the measurement data, the BfS used

• data from the Federal Agency for Cartography and Geodesy with information on location, building characteristics and number of inhabitants of each residential building in Germany as well as
• information on local natural characteristics (radon concentration in soil air, climate, soil and relief characteristics).

These sets of data were incorporated into a statistical model from the machine learning field, which was trained by BfS with the help of the measurement data. The good data basis enabled the BfS to take into account the actual spatial distribution of Germany's inhabitants and the number of storeys of a building in the prognosis and to break down the results to city and municipality level.

Radon situation in situ can only be clarified by measurements

No information about the radon concentration in individual buildings or in the building subsoil of certain plots can be derived from the map.

The radon situation in an existing building or apartment can only be determined by measuring the radon concentration indoors.