In many places, the authorities require certain certificates to be issued before a new building may be used for the purpose for which it was constructed. These may include a building department certificate, showing that the building code has not been violated; a tenement house department certificate permitting occupancy of the building by three or more families; certificates of boards of fire underwriters and departments of gas and electricity as to electric wiring, motors and fixtures; and, in the case of factories and loft buildings, certificates showing the weight which the various floors will sustain.