All persons, natural or corporate, shall have a license to perform contractual work under any of the classifications defined in this chapter. Any persons, natural or corporate, who do work in any of the classifications in this chapter without a license shall be held in violation. Any contractor licensed under this chapter who performs work within the town limits of the city upon a residence, commercial or other building, whether new construction or whether in, about or on an already existing building for which a building permit has not been issued or procured, shall be held in violation of this chapter. (Prior Code, Sec. 4-21)