The document gives common technical criteria to be used for the assessment of laboratories performing heat transfer property measurements of building products and components. It is relevant both to assessments conducted internally and those carried out formally by an accredidation body. It gives contents to the documentation (equipment manual, calibration an maintenance files, measurement procedure document) and the procedure for the assessment of equipment accuracy and performance check. Allsubsequent parts of the series DIN EN 1946 give assessment requirements which are relevant to standards on measurements of specific heat transfer properties.