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 1In 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 (2013/59/EURATOM) [1].NOTE 2Compliance with national exemption levels for NORM nuclides remains.