[en] From the radiological point of view, the use of coal-slags as building material, which may affect indoor doses from external radiation and the inhalation of radon decay products, may be significant. In the most cases the slags have a small radon emanation coefficient, so the use of them as building material does not result in considerable additional dose due to the inhalation of radon decay products. Coal slags were applied as backfill or insulation material underneath the floors and in ceilings. In these buildings the external radiation should be taken into account. The gamma dose rate was measured in buildings (apartments, schools, kindergartens) containing slags with elevated ²²⁶Ra concentration (up to 2500 Bq kg^-1) and with a small radon emanation. The radionuclide (²²⁶Ra, ²³²Th, ⁴⁰K) concentrations of slag samples also were measured. The dose rates caused by slags with different ²²⁶Ra concentration were calculated by modeling too and the shielding possibilities were investigated. According to our measurements the slags with high ²²⁶Ra concentrations increase significantly the gamma dose rates in the buildings. The dose rate values changing with the altitude, so, calculating the dose of people living in these buildings it would be more expedient to use not only the values measured at 1 m height. Using the modeling the expectable dose rates and the thickness of concrete or barite-concrete layers for the wanted degree of decreasing can be calculated. It has been found, based on the modeling, that the dose rate could be decrease with 70-80% using appropriate thickness of concrete or barite-concrete layers. (author)