[en] The so-called 'radiation performance standard' (in Dutch: 'Stralings Prestatie Norm' or SPN) is being developed in the framework of the radon policy in the Netherlands. The radiation performance of a living area results from a calculation of the effective dose rate by external radiation. In the discussions about necessary simplifications in the calculations there is a need for estimates of the actual contribution to the dose rate of external radiation from building materials. Two questions play an important role. How do building type and dimension influence the dose rate? And which parts of a dwelling contribute to the dose rate in specific rooms? This report contains the results of detailed calculations for several versions of a reference dwelling using the model MARMER. From calculations in which type and thickness of a dividing wall between two bedrooms was varied, it was found that the wall shields as much radiation from walls in adjacent rooms as it contributes itself. Between 2% and 30% of the dose rate is due to building materials in other rooms. If adjacent dwellings were included in the calculations, the dose rate for most of the versions of the reference dwelling was estimated to increase by only 5%. For the version with a timber frame this increase could be considerably higher