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.

It is important to comply with the existing legal provisions for moisture protection. Structures with living quarters and/or workplaces, as well as other structures whose intended use requires it, must be permanently protected in all their parts against the penetration of water and moisture from the ground. Special attention must be paid to a tight feed-through of the lines (pipes, cables) through the components in contact with the ground.

Ground probes for heat pumps represent a potential radon entry path due to their depth. Care must always be taken to ensure that the lines (pipes, cables) pass tightly through the components in contact with the ground - for example, by using a pipe penetration system (annular space seals, lining pipes, wall collars, etc.).

In the case of geothermal heat exchangers, air wells and similar systems, it must be ensured that no soil air containing radon enters the building via the ventilation system.

Air-earth heat exchangers must therefore be designed with airtight pipes (plastic) with tight joints. An alternative to the airtight design would be to operate the ground register in positive pressure.

For air wells, the gravel filling must be limited laterally and downwards by an impermeable layer (impermeable soil, for example clay or foil (thickness ≥ 0.5 mm)). Suitable precautions must be taken for the discharge of water from the air well (for example pumping out, siphon). A control measurement to check the annual mean radon concentration in the building is recommended in this case.

Translated with www.DeepL.com/Translator (free version)

Underfloor extraction (radon drainage)

This measure is primarily used to create a negative pressure underneath the floor slab opposite the building. This reduces convective radon ingress from the soil. Inlets and outlets through building components in contact with the ground for electricity, water, wastewater, etc. must be tightly sealed (for example, by means of feed-through systems for pipes and cables).

Drainage pipes with a diameter of at least 8 cm are to be laid under the continuous foundation slab or the floor slab (in the case of strip foundations). The method of pipe laying depends on the permeability of the surrounding material. If gravel or crushed stone is installed, the pipe system is laid in a serpentine form with a pipe spacing of up to 8 m and joined together to form an exhaust pipe (solid wall pipe).

If the pipe system is installed directly into the ground (pipe protection by gravel and/or fleece), a smaller distance of 1 to 3 m is required. A minimum distance of 1 to 2 m must be maintained from the outer walls. In order for a negative pressure to be built up in the radon drainage system, an inflow of air from the water drainage system must be prevented (separation of the systems, for example, by foundation or foil).

Note on subsoil suction in highly permeable soils: In the case of gravel soils and highly fissured soils (e.g. karst areas), no negative pressure can be built up under the floor slab without additional measures. Under the radon drainage system, therefore, the permeability to the soil must be greatly reduced with lean concrete or a foil.

If the control measurement shows an increased radon concentration, a fan for active negative pressure generation must be used for both design variants. It is essential to take into account the formation of condensation in the pipe system and the noise generated by the fan. The air outlet should be located at least 2 m away from windows and doors.

The ventilation system should - if technically possible or if there are no objections based on building physics - be operated pressure-neutral or with a slight overpressure (a few pascals).

The fresh air intake outdoors should be placed at least 1.5 m above the ground (for example, no intake from basement window shafts, as the radon concentration is higher near the ground).