Radon - influence of energetic (thermal) renovation Properties, occurrence and effect of radon

Properties and occurrence

Radon is a naturally occurring radioactive noble gas that is colorless, odorless and tasteless. It is a decay product of the radioactive heavy metal uranium found in soils and rocks. Radon escapes from soils and rocks into the soil air. With the soil air, it can enter the indoor air of buildings.

An initial indication of whether elevated radon concentrations can be expected in the indoor air of buildings can be obtained from the national radon maps. Only a measurement can give certainty about the radon concentration in the respective building.

Detailed information on radon can be found on the country-specific websites. These addresses are listed on the back of this brochure.

Note: National specifications or recommendations may differ from the present contents!

Annual mean radon concentrations normally range from 50 to 500 becquerels per cubic meter of air. However, values up to several 1,000 Bq/m³ can also be reached - especially in radon areas.

A map of Central Europe with color-coded distribution of radon concentration. With elevated values in the north of Austria as well as in the southeast of Switzerland and in South Tyrol. — Distribution of radon concentration in Central Europe, arithmetic mean of indoor measurements on the ground floor (10-x-10-km grid).

Pictographic image of a human torso with nasal and pharyngeal cavities and lungs highlighted. Indicates inhale and exhale with arrows.

Effect on health

After smoking (about 85%), radon and its decay products are a leading cause (5 to 10%) of lung cancer. In people who have never smoked, radon is the most common cause of this type of cancer. Radon and smoking reinforce each other in their harmful effects on human health. Most of the radon inhaled through the air is exhaled again. The greatest health risk is therefore not posed by the radioactive noble gas radon itself, but by its short-lived decay products (radioactive heavy metals).

The free decay products present in the indoor air attach themselves to airborne suspended particles (aerosols). When breathing, the aerosols with the attached radon decay products are deposited in the lungs. From there, they emit ionizing radiation that can damage the immediately surrounding lung tissue and ultimately cause lung cancer.

Reference values and threshold values

The following table shows the current reference values and thresholds for annual mean radon concentrations in homes or workplaces of the different countries.

Country/Region	Reference values for existing buildings	Reference values for new buildings	Threshold values
Germany	300 ^Bq/m3	300 ^Bq/m3	-
Austria	300 ^Bq/m3	300 ^Bq/m3	-
Switzerland	300 ^Bq/m3	300 ^Bq/m3	*1,000 ^Bq/m3
South Tyrol	300 ^Bq/m3	**200 ^Bq/m3	-

* for workplaces

** for living quarters as of 31.12.2024

Factors influencing the indoor radon concentration

The level of radon concentration in indoor air depends on various factors.

Subsoil properties of various soil types shown pictographically. From pebbly to clayey).

Composition of the subsoil

In addition to the composition of soil and rock (uranium, radium content), the grain size of the rock (release of radon to the soil air) and the permeability of the subsoil (onward transport of the radon-containing soil air) play an important role. Special caution is required for rubble cones and slopes, weathered granite, karst and gravel soils (high radon availability due to good permeability) - in contrast to very compact or clayey soils.

Pictogram of a house with a permeable foundation over which radon entry is indicated by means of arrows.

Building condition

The permeability of a building to soil air in the foundation area as well as in walls in contact with the ground is decisive. Possibilities of penetration exist, for example, through cracks and crevices as well as along cable and pipe penetrations. The radon-containing soil air is sucked into the building by a negative pressure created in the building (chimney effect due to temperature differences between room and outside air or due to wind pressure). If cellars or other building areas with ground contact are open to floors above, radon can spread upwards particularly easily.

Pictogram of a house where air exchange between indoor and outdoor air is indicated by means of arrows.

Air exchange in the building

The exchange between indoor air and outdoor air has a significant influence on the level of indoor radon concentration. Leaky windows and doors lead to higher air exchange rates. If, on the other hand, the air exchange rate is reduced, for example by installing tightly closing windows and doors, the radon concentration in indoor spaces can increase considerably.

Notes on energy (thermal) refurbishments

Energy (thermal) renovations change the tightness of the building envelope - for example, by installing tight windows and exterior doors or vapor barriers in the roof area. This affects the pressure conditions, the air exchange rate and thus the radon ingress rate.

If thermal insulation on the façade is not installed in accordance with the latest state of the art, radon-containing soil air can rise via cavities between insulation and walls in contact with the ground and enter the interior of the building via leaks.

These effects can lead to a significant increase in indoor radon concentrations.

Photo of a house with a thermal image of the same house in the foreground. — Renovations affect the tightness of the building envelope.

A person seen from the back, doing renovation work on the windows. — Renovations affect the tightness of the building envelope.

Detail photo of an improper execution of thermal insulation on a facade. — Only professional designs prevent the rise and penetration of soil air containing radon.

Procedure for energy (thermal) refurbishment

Determination of the actual radon status

The actual radon concentration in a building can only be determined by measurement. As a rule, such a measurement is carried out indoors with passive radon measuring devices. These measuring devices are small, and performing the measurement is simple and inexpensive.

A radon measurement should ideally be carried out before any building renovation. This is especially true for homes with living spaces and/or workplaces in contact with the earth, and for homes in radon areas. If the measurement reveals an elevated radon concentration, this circumstance should be taken into account when planning the renovation.

Possible measures in case of elevated radon concentrations are explained in more detail in the brochure "Radon - Remediation Measures for Existing Buildings".

You can find out about recognized bodies in your area from the respective specialist bodies in the individual countries (see here).

Size comparison of passive measuring devices with a one euro coin. — Passive measuring devices for the determination of radon concentration

Facts and advice

Radon is the second leading cause of lung cancer after smoking.
Radon enters buildings from the ground through leaks.
National radon maps are a first source of information.
Only a measurement can give certainty about the radon concentration in the respective building.
Energy (thermal) renovations can increase the radon concentration.
After completion of the energetic (thermal) renovation, a long-term measurement is recommended.
Inspections of the renovation measures every five years or maintenance according to specifications are recommended.

Observation of notes on radon protection

In consultation with building experts and radon specialists, the following instructions should be observed during energy-related (thermal) renovation:

If remodeling work is carried out in the course of energy (thermal) renovation in living areas with ground contact on floors and walls, radon protection measures can be implemented much more cost-effectively and effectively than after the fact. Relevant information can be found in the brochure "Radon - Remediation Measures for Existing Buildings".
If only the lower half of the building is sealed, the installation of an outside air diffuser (ALD) to reduce negative pressure in the basement (pressure equalization) is recommended as a radon protection measure.
The rising of radon-containing soil air via cavities between insulation and exterior wall or the penetration into the building interior via leaks in the masonry or walls must be avoided. This is ensured if the work is carried out properly according to the state of the art (for example, adhesive application using the edge bead point method or over the entire surface).
Preventing the flow of air from the basement into the living spaces by sealing - for example, by means of tight doors between the basement and the living space - has a positive effect on both the heat balance and radon protection.
The installation of controlled residential ventilation is a beneficial measure with regard to radon. It must be ensured (and regularly checked) that there is no negative pressure in the building (attention: consider aspects of building physics).
When installing a single combustion system (e.g. tiled stove, kitchen stove, fireplace), ensure that there is a sufficient supply of outside air. If technically possible, a direct supply of outside air is preferable.

Control of radon concentration after energetic (thermal) refurbishment

In order to make sure that the energetic (thermal) renovation has not caused an increase in the radon concentration, it is recommended to measure the radon concentration after the completion of the construction works.

If an elevated radon concentration was detected prior to the energy (thermal) retrofit, a radon measurement must be performed in any case after the retrofit.