Radon in new buildings

Radon prevention in new construction is important in order to ensure low radon concentrations in indoor air. Radon prevention in the construction phase is easier and less expensive than implementing mitigation measures afterwards. Use of radon-safe building methods is justifiable anywhere in Finland. The aim should be to keep the radon concentration as low as possible, as the higher the radon concentration and the longer you stay in it, the greater the risk of lung cancer associated with radon.

The key question in radon prevention is the blocking or reduction of radon-bearing air flow from the soil. The most common foundation type for low-rise residential buildings in Finland is a floor slab cast inside a footing. Between the slab and the footing, there is normally a gap through which radon can seep into the building. Using lightweight concrete blocks as the foundation wall material can make the situation worse. The same problem is met when lightweight concrete blocks are used as the material of walls in contact with soil in hillside houses or houses with a cellar, instead of cast concrete. These detriments can be easily prevented by sealing the base floor and wall structures and installing radon piping.

A base floor with a crawl space is a radon-safe solution, if radon is prevented from entering the house by sealing base floor joints and penetrations and ensuring sufficient ventilation of the crawl space. Sufficient ventilation is achieved by following the regulations concerning the size and number of vents.  The third radon-safe solution is a monolithic slab foundation which has no leaking gaps or joints. The sealing of the penetrations must be ensured also with this solution.

In new buildings, mechanical supply and exhaust ventilation is the best solution for radon prevention. Even if the ventilation is adjusted to balance, the temperature difference between indoor and outdoor air causes underpressure at the floor level. This underpressure forces the radon-bearing air in the soil to flow into the house. However, the building's ventilation must not be adjusted to overpressure due to the risk of moisture damage. Ventilation must always be designed and implemented in accordance with building codes and related instructions.

Leakage routes of radon-bearing air in slab-on-ground foundation. Radon-laden air ingresses the building through the pull-throughs, holes and gaps in the foundation.
Leakage routes of radon-bearing air in slab-on-ground foundation. Photo: Symboli.fi


Radon-safe building methods are, as a rule, justifiable in the entire country, as values exceeding the reference level of 200 Bq/m3 without radon prevention is common. It is not worth carrying out soil radon measurements, as radon prevention is cheaper than a radon survey of a single plot of land.  

In addition to reducing radon levels, radon-safe building methods can improve indoor air quality in other ways. A radon-safe solution prevents musty odours and any other hazardous gases from soil from seeping into the building. Radon piping also removes moisture from the base floor.

The architect and builder should always be required to comply with the instructions of the RT reference card on radon-safe design and construction. Radon prevention solutions are marked on the foundation, structural and HVAC drawings. During construction, it is important to oversee that radon prevention is carried out as planned.


Methods for radon prevention

Finally, remember to carry out radon measurements for at least two months 

After the completion of the building, it is advisable to carry out a radon concentration measurement to ensure that radon protection is successful and to detect possible construction errors. The measurement should be carried out immediately during the first year when the warranty is still valid and the construction company is obligated to take any necessary measures to reduce the radon concentration. In order to obtain a reliable result, heating and ventilation systems must be completed and in normal use. If the radon concentration exceeds the reference value of 200 Bq/m3, it is easy to reduce the radon concentration by connecting an extractor fan to the exhaust duct. 

Do you have questions about radon prevention?

You should first contact the building supervision of your municipality or the supervisor or structural designer responsible for your construction project.

Contact Us:
[email protected]