Abstract: A rain water outlet for a roof of a building comprising a vertical pipe and a trough fixed to the upper end of said pipe. A lid is fastened in the trough above the inlet end of said pipe. The lid forms a closed surface larger than the inlet end to cause water to flow radially in the trough to said inlet end and to prevent axial suction of air into the pipe. A sieve is positioned between the lid and the bottom of the trough to surround said inlet end. The sieve is provided with perforations through which water flows from the trough into said inlet end. The relation between the total area of the perforations of the sieve and the cross-sectional area of the outlet pipe is between 2.5 and 3.5.