Experiences in radon-safe building in Finland

A study was made of radon-safe buildings in 300 Finnish low-rise residentia l buildings using data obtained from a questionnaire study. The study also aims at finding the main defects in design and implementation and how the g uidance given on radon-safe buildings in slab-on-grade houses has been foll owed. According to the guidelines, the prevention of the flow of radon-bear ing air from the soil into the house is recommended to be carried out throu gh installation of aluminised bitumen felt and use of elastic sealants. Sec ond, as a precaution perforated piping should be installed in the subsoil o f the floor slab. The median indoor radon concentration in the houses was 1 55 Bq/m(3). This is 32% lower than the median of the estimated reference va lues. The action level of 200 Bq/m(3) was still exceeded in 40% of the hous es. In most houses with slab-on-grade the prevention was based only on the installation of a sub-slab depressurisation system. Sealing was performed i n a low number of houses. In 80% of houses with a sub-slab piping connected to an operating fan, radon concentration was below the action level of 200 Bq/m(3). In houses with piping but no fan, the corresponding fraction was only 45%. Sub-slab piping without a fan had no remarkable effect, on radon concentration. In houses with crawl-space and edge-thickened slabs, radon c oncentrations were low. The choice of foundation system thus significantly affects the indoor radon concentration. The importance of complete and care ful sealing work should be stressed in advice and guides concerning radon p revention. (C) 2001 Elsevier Science B.V. All rights reserved.