Radon Mitigation in Blocks of Flats

The average indoor radon concentration in Finnish flats is 80 Bq/m3. Typically walls have been made using concrete elements. Building materials are the dominant source of indoor radon. However, in the flats of the lowest floor, with a floor slab in direct ground contact, the main source of radon is often the inflow of radon bearing soil air. The number of these ground contact flats is less than 10 % of the total number of flats. The average indoor radon concentration of these ground contact flats is 150 Bq/m3. Consequently in more than 10 % of these dwellings the concentration limit of 400 Bq/m3 is exceeded. The data presented is based on a nation-wide radon survey in 900 flats. Highest concentrations observed in flats have exceeded 10.000 Bq/m3.