Every owner of every house, building, or structure under construction, except buildings to be used exclusively for residential purposes, shall affix and display conspicuously on each floor of the building a placard stating the load per square foot of the floor surface which may safely be applied to that particular floor during construction. If the strength of the floor varies in different places, he shall affix placards for each varying part of the floor.
All such placards shall be verified and approved by the city engineer or inspector of buildings or other proper authority of the city charged with the enforcement of building laws.
No one shall load any such floor or any part thereof to a greater extent than the load indicated on the placard.