Section 23(4)(viii) in The Chennai City Corporation Building Rules, 1972
(viii)The inside of every chimney or flue shall be properly rendered or pargetted as such chimney or flue is carried up, unless the whole chimney or flue shall be lined with fire brick or fire proof piping of fire clay at least two and a half centimetres thick and unless the spandrel angles shall be filled in solid with brick work or other incombustible material;