No person shall engage in the business of plumbing or represent himself or herself to the public as engaging in the business of doing plumbing work within the City without having first obtained a plumbing contractor’s license issued by the State of Iowa. However, this license requirement does not apply in cases where the owner of a single-family dwelling desires to install or repair the plumbing equipment in his or her own primary residence and the owner appears before the Building Official and shows that he or she is competent to do the specific work for which the permit is desired. All work performed within rental units shall be by a state licensed contractor. All work must meet the requirements of the adopted Plumbing Code and shall be inspected.