Public halls and stairs, lighting and ventilation of. In all multiple-dwellings erected prior to the passage of this act the public halls and stairs shall be provided with as much light and ventilation to the outer air as may be deemed practicable by the health officer or by such other appropriate public official as the mayor may designate, who may order the cutting in of windows and skylights and such other improvements and alterations in said dwellings as in his judgment may be necessary and appropriate to accomplish this result. All new skylights hereafter placed in such dwellings shall be in accordance with section 27 of this act and shall be of such size as may be determined to be practicable by said health officer, or by such other appropriate public official as the mayor may designate.