Radon levels in rented accommodation

Indoor radon levels were measured in 221 homes located in 53 buildings, including 28 multi-occupant houses and 25 single-family terraced houses. The homes consisted of rented accommodation located in buildings recorded as being constructed before 2010 and after the year 1850. In addition, the radon level was measured in the basement in 9 of the buildings.
The mean year value of the indoor radon level was 30.7 (1–250) Bq/m3. The indoor radon level exceeded 100 Bq/m3 in 5.9% of the homes, all located in single-family terraced houses. The variable single-family terraced houses explained 5.9% of the variation in indoor radon levels, and although associations were positive, none of these, besides homes in single-family terraced houses, were statistically significant. Approx. 75% of homes exceeding 100 Bq/m3 indoor radon level had levels between 100 and 200 Bq/m3 and 25% had indoor radon levels exceeding 200 Bq/m3. Significant differences in indoor radon levels were found in homes located in multi-occupant houses. Additionally, the risk of indoor radon levels exceeding 100 Bq/m3 in homes in multi-occupant houses was found to be very low, but the risk was highest on the ground floor in a building constructed with slab on ground.