This European Standard applies to wastewater drainage systems, which operate under gravity. It is applicable for drainage systems inside dwellings and commercial, institutional and industrial buildings. This third part of this European Standard describes a method of calculating the hydraulic adequacy of non-siphonic roof drainage systems and gives performance requirements for siphonic roof drainage systems. It also sets standards for the layout and installation of roof drainage insofar as they affect flow capacity. This part of this European Standard applies to all roof drainage systems where the outlets are large enough not to limit the flow capacity of the gutter (i.e. free discharge conditions). It applies to all materials used for roof drainage systems. Detailed information additional to that contained in this Standard may be obtained by referring to the technical documents listed in Annex B.