Section 47(iv) in Faridabad Complex Administration Building Rules, 1989
(iv)the cavity may be reckoned as part of the thickness prescribed for walls by these rules where such thickness does not exceed 20 centimetres but shall not be so reckoned where such thickness exceeds 20 centimetres. All external cavity walls shall be ventilated and drained properly. The normal rule in that combined thickness of the walls (excluding cavity) should be equal to the thickness demanded for any solid wall with the given conditions for height and length. If the internal wallis half brick thick, it shall be laid in cement sand mortar 1:4 and reinforced with hoop iron as the outer wall.
