Section 118(3)(a) in West Bengal Municipal (Building) Rules, 2007
(a)windows having an area of not less than 10 per cent of the floor area and located in an exterior wall facing a street alley yard or an airshaft whose dimension in the direction perpendicular to the window is not less than 1/3 of the height of the building on which ti, window is located subject to a maximum and a minimum limit of 6 m (20 ft) and 1 m (3 ft) respectively;