Principal investigator: Hannu Arvela, Head of laboratory, Radiation and Nuclear Safety Authority, e-mail: hannu.arvela@stuk.fi

The study aims at combining the construction of a good radon-tight foundation and moisture prevention in new low rise residential houses. The study aims also at developing the applicability of different ventilation strategies, the control of de-pressure in dwellings and use of fresh air vents for reduction of indoor radon concentration. The study also deals with the radon safe foundation construction of blocks of flats. Without any radon prevention the recommended limit for new houses, 200 Bq/m3 will be exceeded in 50 % of new houses in wide areas of the southern Finland. The recommended radon safe construction of a slab-on-grade foundation is based on the use aluminized bitumen felt which seals the foundation and prevents the leakage of radon-bearing soil air into living spaces. The construction provides also a qualified moisture prevention against moisture originating from the subsoil. Radon safe construction will be compared with the normal moisture prevention, using simulation calculations. In some houses the moisture of house constructions and subsoil will be measured.

The study will be carried out in 15 single family houses where the radon safe constructions will be controlled by experts of this project. Indoor radon concentration, air exchange rate, de-pressure and the operation of air exchange instrumentation will be measured carefully. This provides a basis for estimating the radon entry rate into the houses and the success in radon prevention. The direct influx of radon-bearing soil air increases also the indoor radon concentration of flats of the lowest floor dwellings, in some cases also in upper floors. In this study the alternative radon foundation constructions of apartment houses will be surveyed, measurements will be made in 5 test houses. The de-pressure in flats has also a remarkable effect on indoor radon concentrations. The applicability of fresh air vents in flats for reduction of de-pressure, radon concentration and generally the indoor air quality will be studied in test houses and laboratory. The effect of commercially available fresh air vents on de-pressure and draft will be studied.