The aim of this Technical Report is to propose a methodology to determine indoor gamma dose from building materials and to help classify such a product as required in the Construction Products Regulation [7]. This first technical approach could be a precursor for the development of a harmonized European Standard based on this methodology. NOTE 1 In this Technical Report, doses from radon and thoron exhalation are excluded. However, in 3.3, information is given on how radon exhalation is dealt with in (EU)2013/59/Euratom, the Basic Safety Standards Directive (Euratom-BSS) [1]. NOTE 2 Building materials considered in this Technical Report are the construction products used for buildings. Other construction products used for any other construction works (civil engineering& ) are not relevant and out of the purpose of the scope of this Technical Report. NOTE 3 Compliance with national exemption levels for NORM nuclides remains.