A calculation model for determining the indoor dose due to building materials with significant concentration of radioactivity has been applied to the case study of ceramic tiles; the model allows the contribution of bearing walls and wall covering materials to be calculated. The model is implemented in FORTRAN 77 and provides a quantification of the gamma radiation field (in terms of external dose rate in air, nGyh21) inside a room with known dimensions. Application model results have been validated both by comparison with the results obtained by other authors and by experimental measurements. Model sensitivity and performances have been analysed and lastly the case studies focused on ceramic tiles have been proposed.