RESRAD-BUILD is a code developed by Argonne US National Laboratory for assessing the radiological doses resulting from the occupancy of buildings contaminated with radioactive material. This freely downloadable software allows to consider multiple sources of contamination and to assess not only the external exposure pathway but also the dose resulting from inhalation or ingestion of contaminated dust as well as the dose from inhalation of radon. The software offers the possibility to assess in a flexible way the external dose from the natural radioactivity of building materials. A room model similar to the one used for deriving the activity concentration index of the 2013/59/euratom directive may easily be implemented and gives consistent results. A comparison is made with the calculations performed in the CEN technical report on dose-assessment of gamma radiation from building materials. An example of assessment of the external dose resulting from multiple layers of building materials is given where measurements data are used for the activity concentrations. The assessment allows demonstrating compliance with the reference level set up in the directive.