This document specifies the requirements for solid wall pipes with smooth internal and external surfaces, extruded from the same formulation throughout the wall, fittings and the system of unplasticized poly(vinyl chloride) (PVC-U) piping systems in the field of non-pressure underground drainage and sewerage: — buried in ground outside the building structure (application area code "U"), and — both buried in ground, within the building structure and outside the building (application area code "UD").