Hanging flues i e., for the reception of stovepipes built otherwise than from the ground) shall be allowed only when built according to the following specifications. The flue shall be built four inches thick, of the best hard brick, laid on flat side, never on edge, extending at least three feet above the roof and always above the comb of the roof and lined on the inside with cast-iron or fire-clay flue lining from the bottom of the flue to the extreme height of the flue, the ends of all such lining pipes being made to fit close together and the lining pipe being built in as the flue is carried up. If the flue starts at the ceiling and receives the stovepipe vertically, it shall be hung on iron stirrups, bent to come flush with the bottom of ceiling joints. All flues shall have a proper and sufficient support at their base and in no case shall they be supported even partially by contact in passing through partitions, ceilings or roofs. Flues not lined as above shall be built from the ground eight inches thick, of the best hard brick, with the joints struck smooth on the inside. The flues of every building shall be properly cleaned and all rubbish removed and the flues left smooth on the inside upon the completion of the building.