This International Standard establishes general principles regarding the procedure used in the construction and quality assessment of butt fusion joints incorporating fittings (ISO 8085‑2) and pipes used in the construction of gas (ISO 4437) and water (ISO 4427) distribution systems made with equipment that complies with ISO 12176-1 and installed in accordance with ISO/TS 10839, relevant codes of practice, national regulations or industry guidance. Specifically, this International Standard specifies a number of proven butt fusion jointing procedures for pipes and fittings with a wall thickness up to and including 70 mm. This International Standard takes into consideration the materials and components used, the fusion jointing procedure and equipment and the quality assessment of the completed joint. It can be applied in conjunction with appropriate national regulations and standards.