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This document describes a calculation method to determine the indoor gamma dose from construction products. The method includes calculation of the indoor gamma dose from the individual construction product under its intended use, as well as the dose from the building taking consideration of multiple building materials where this is deemed necessary and any shielding from the terrestrial background. The calculation method builds on existing modelling principles for photon emission and absorption. Parameters of the modelling that are not product specific, such as room geometry, exposure coefficients, and conversion factors are predefined and form the underlying basis for the method in this EN. The choice for pre-defined model parameters is essential from a harmonization perspective, despite the fact that such parameters can vary considerably for every homeowner, building type, region or country. Typical examples are the exposure time, the location of exposure in the building, the terrestrial background radiation and the amounts and way the building materials are used in the building. The parameters are selected on the basis of international consensus, as laid down in ICRP, UNSCEAR, EU RP guidelines and other renowned publications. Product specific parameters such as density and thickness are specified in accordance with the product’s intended use. In addition, the products’ massic activities of 226Ra, 232Th and 40K are specified and obtained according to prEN 17216 (under development, [3]). The method provides a tiered approach with a basic approach intended for assessing individual construction products, followed by a more refined approach to assess a complete building design. The former approach assumes an identical structure of building materials on all six surfaces of the model room, and where needed complemented with other building materials that form an intrinsic part of the product’s intended use. The latter approach enables evaluation of a known building design. Here the user can specify the applied construction product to walls, floor or ceiling separately in accordance with the product’s intended use. The indoor gamma dose from the individual construction product as well as the building is expressed in terms of an annual effective dose from gamma radiation in the indoor environment. The formulation of the indoor gamma dose in the building is consistent with the dose for indoor external exposure as stated under Article 75 of the Basic Safety Standards Directive. As a result, the described method enables assessment of the calculated annual dose of the building against the reference level as defined in the Basic Safety Standards Directive . The method is designed for assessment of mineral based building materials applied in bulk or superficially and used as a construction product in buildings. This includes any building materials that have been identified by EU member states as being of concern from a radiation protection point of view. The method is envisaged for use by producers of building materials, architects and building constructors as well as authorities. NOTE It is important to state that following the calculation of dose, any subsequent regulatory classification falls explicitly outside the scope of this method and is the responsibility of the relevant authorities.