Section 67(5) in Kolkata Municipal Corporation Building Rules, 2009
(5)For the purpose of this rule, if any interior open space or courtyard enclosed on three sides by a building or part there use of is meant to serve lighting and ventilation purpose to a part or whole of one side of one or more habitable rooms, then the minimum width of such open space shall be 2.4 m. for buildings upto 15.5 m. in height; 3.5 m. for buildings above 15.5 m. upto 25.5 m. in height; 5.0 m. for buildings above 25.5 m. up to 40.0 m. height; and 7.0 m. for all buildings above 40.0 m. in height.Provided that the depth of such open space shall not exceed twice its width and the same may be reduced to 1.2 m. if no habitable room, or balcony attached to the habitable room is facing the interior open space. However, in case the depth of such interior open space is less than the width, the same shall not be considered as interior open space, but be called as "notch" and the same will be permitted without any restriction.
