Applicability of section. The following regulations shall govern the erection and alteration of buildings or structures and the use of land in the Rural Districts, except that they shall not apply to existing buildings or structures nor to the existing use of any building or structure but shall apply to any alteration of a building or structure for use for a purpose or in a manner substantially different from the use to which it was put before alteration. However, no building or structure qualifying as a nonconforming use shall be occupied for a greater portion of the year than such building or structure was occupied as a prior nonconforming use unless minimum lot size, setbacks, frontage, building line, and all other dimensional requirements for this district are met or a variance is granted by the Board of Adjustment. In either case, the requirements for septic systems, as stated in Chapter
391, Article
I, of the Salem Code, shall be met. Additionally, no building permits or variances shall be granted that would be likely to result in an increase of the portion of the year during which a building or structure qualifying as a nonconforming use will be occupied if such increased occupation will affect adversely public health standards, water quality, sewage treatment requirements or the water quality of any lake, stream or surface water system. The restrictions of §
490-202, minimum lot size, setbacks, and minimum width at the building line, and §
490-804, Proximity to water bodies, shall not apply to lots shown in a plat approved by the Salem Planning Board prior to the adoption of this chapter until January 1, 1981, except that if two or more lots are contiguous and are held in identical ownership and none of the lots are improved by a house, then the restrictions of §
490-202, minimum lot size, shall apply forthwith. Discontinuance of a nonconforming use for whatever reason for 12 consecutive months shall subject such property to all of the requirements of this section.