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Norwegian Radiation and Nuclear Safety Authority

Radon mitigation measures

If radon levels of over 100 Bq/m³ have been measured in your residence, radon mitigation measures should be implemented in order to reduce these levels.

Last updated: 19. mars 2021 11:05


Five steps for reducing radon levels in your home:

  1. Contact a radon mitigation professional. 
  2. Determine the source of the radon problem. 
  3. Implement radon mitigation measures that target the source of the problem. 
  4. Re-measure radon. 
  5. Maintenance. 

Radon levels should be as low as reasonably achievable and always under 200 Bq/m3. By implementing radon mitigation measures, the overall radon levels should be considerably reduced. 

Contact a radon mitigation professional 

The Norwegian Radiation and Nuclear Safety Authority (DSA) recommends engaging professional services in order to implement radon mitigation measures. There are a number of companies who have specialized themselves in giving advice on radon reduction measures. Companies may be found on the internet or via other information services. The trade association Norwegian Radon Association (Norsk Radonforening) has a list of their members on their web site. There are also other companies. There is no public approval system of firms carrying out mitigation measures, and DSA does not recommend any one particular firm. 
DSA recommends that you take the following points into consideration when selecting a firm:

  • Contact several firms, ask what they can offer and compare these offers and prices.

  • Enquire about the firms’ qualifications/experience. You can also request references from previous work that they have carried out.

  • A good radon mitigation professional has experience with the various types of mitigation measures used to reduce radon. Professionals should update their competence regularly. This may be carried out by attending appropriate courses.

A radon mitigation professional should help you: 

  • Determine the source of the radon problem. 

  • Implement long-lasting mitigation measures that primarily target the source and therefore prevent radon from entering the building. 

  • Ensure that you have adequate basis for implementing mitigation measures in the building. This can be done by either engaging the services of a tradesman or by carrying out the work yourself. Alternatively the radon mitigation professional may assist with any necessary rectification work. 

Determine the source of the radon problem

There are primarily three sources to radon in indoor air: 

  • The ground 

  • Household water supply 

  • Building materials and construction aggregates 

The ground 

The most common source of the radon problem is the ground under the house. Soil gas, which contains radon, enters the building through openings and gaps. Typical gaps are cracks and untreated porous light expanded clay aggregate concrete bricks. Other examples may include gaps around pipes or cables and joints where the floor meets the wall. Due to the fact that indoor air pressure is in general slightly lower than outdoor air pressure, radon tends to be drawn from the soil into the building. This is particularly true during the winter due to the fact that houses are heated up. 

Household water supply 

Household water may also be a source to the radon problem in particular if the water comes from a water well. Water from bore holes is particularly at risk of having elevated levels of radon. The health risks, with respect to radon in drinking water, are primarily associated to the inhalation of radon which is released into the indoor air. When water is used, for example during showering or in the dishwasher, radon escapes from the water into the air, thereby increasing the level of radon in indoor air. 

Building materials and construction aggregates 

Filling material, beneath buildings, which is composed of rocks with a high level of uranium and radium, can significantly contribute to the level of radon in indoor air. Other types of building materials are a less likely source of radon in Norway. Materials made of stone, such as cement for example, may discharge radon if the material is composed of rocks with a high level of uranium and radium. 

Implement radon mitigation measures which target the Source

DSA recommends that measures implemented to reduce radon primarily target the source. In other words that implemented measures address the source of the radon problem and thereby prevent radon entering the building. The type of measure, or combination of measures, which is/are best, needs to be assessed for each individual case. 

If the ground under the house is the source of the radon problem, an attempt to determine radon’s entry points need to be made. This needs to be done in order to ensure that the implemented measures can effectively target the source of the problem.

There are three main types of measures which may be implemented in order to reduce radon in indoor air. Various measures may be implemented simultaneously. 

  • Soil depressurization 

  • Sealing foundation cracks 

  • Ventilation 

If the ground under the house is the source of the problem, soil depressurization under a building is often the most effective means of reducing radon. This measure may be combined with other measures such as sealing foundation cracks and openings.

Sealing the gaps alone is not necessarily sufficient to solve the radon problem. The effect of various ventilation solutions can vary and is determined by (for example) the size of the radon problem as well as the original ventilation system.

A balanced ventilation system is not necessarily the best solution to a radon problem and other measures should often be considered first. Measures, such as passive soil depressurization, should be easy to activate by using a fan. 

In the case of household water supply being the source of the radon problem, several solutions are available on the market which can address this problem. Common techniques include aeration, filtration or storage. 

A combination of ventilation and sealing of cracks is often the best way of reducing radon levels in the case of the building materials being the source of the radon problem. 
Measures implemented to reduce radon should: 

  • Be able to reduce radon concentrations considerably below the reference level. 

  • Be safe and not creating back-drafting. 

  • Be durable and functional for the expected life of the building. 

  • Provide easy monitoring of the performance. 

  • Be quite and unobtrusive 

  • Have low costs for installation, operation and maintenance. 

The article continues under the illustration.

Bilde av hus med radonbrønn
Active soil depressurization is a measure that is commonly implemented to reduce radon. III.: DSA/Monica Egeli

The SINTEF Building Research Design Guides is a complete source to technical solutions for buildings. An article has been published in the “Building Research” series that gives a technical description of the measures which may be implemented in order to reduce radon in existing buildings. The publication may be ordered at SINTEF Byggforsk. Information is also available on the Norwegian Building Authority webpage.

Re-measure radon 

Following implementation of measures for reducing radon levels, radon should be re-measured. It is only by re-measuring radon levels that it is possible to determine whether or not the implemented measures have had the desired effect. If this is not the case, further action should be taken. 


Measures implemented to reduce radon should be frequently checked in order to ensure that they still function as they should. This includes verifying that fans and other electrical equipment work and that pipes transporting radon-containing soil gas are whole and undamaged. It is also important to ensure that leakages have not occurred in areas which have been sealed. Frequent radon measurements are an ideal way of checking that the implemented measures work. How often this should be carried out, varies from case to case but once every five years can be a good place to start. 

Consider implementing temporary measures 

If the levels of radon which have been measured are very high, it is worth considering implementing temporary measures. At least until more permanent measures are in place. The aim of temporary measures is to attempt to reduce the level of radon exposure. However it is important to remember that these measures cannot replace a more permanent solution. The higher the radon levels the greater the need to implement temporary measures to reduce radon. 

Temporary measures may include reconsidering how a room is used, for example moving the bedroom to another room in the house with lower levels of radon. 

Other types of temporary measures are increasing ventilation/airing of the room by opening air vents and more frequently opening windows. Sealing visible cracks, where soil gas and radon may seep in, may also provide a temporary solution to your radon problem. The effect of the aforementioned temporary measures may vary considerably and can be assessed by a radon measurement. 

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