All work done by contract or subcontract or any building or improvements or work on roads, bridges, streets, alleys, or buildings for the city shall be done under the provisions of this chapter; provided, that in cases of extraordinary emergency which may arise in time of war, or in case where it may be necessary to work more than eight hours per calendar day for the protection of property or human life, the hours for work may be extended; but in such case the rate of pay for the time employed in excess of eight hours of each calendar day shall be one and one-half times the rate of pay allowed for the same amount of time during eight hours’ service. For this purpose, this chapter is made a part of all contracts, subcontracts, or agreements for work done for the city. [Code 1980 at § 13.16.030].