Describes the requirements for solid wall pipes with smooth internal and external surfaces extruded from the same compound/formulation throughout the wall, fittings and the system of polypropylene (PP) piping systems intended for use for: - non-pressure underground drainage and sewerage outside the building structure (application area code 'U'), and - non-pressure underground drainage and sewerage for both buried in ground within the building structure (application area code 'D') and outside the building structure.