The owner of every house, building or structure, except a private barn or a private house, shall affix and display conspicuously on each floor of such building during construction, a placard, stating the load per square foot of floor surface which may, with safety, be applied to the particular floor during construction. If the strength of different parts of any floor varies, then there shall be placards for each varying part of such floor. It shall be unlawful to load any such floors, or any part thereof, to a greater extent than the load indicated on the placard, and all such placards shall be verified and approved by the Department of Labor, or other proper authority in the city or village charged with the enforcement of building laws.