Existing zone lots of record. In any residential district, only a single-family detached dwelling may be erected on a nonconforming zone lot of record at the effective date of this chapter, and then only if the owner does not own any adjoining property which would create a conforming lot if all or part of said adjoining property were combined with subject zone lot, provided however, that no lot or lots shall hereafter be reduced so as to create one or more nonconforming lots, and provided that for any such preexisting nonconforming zone lot of record, no side yard shall be less than five feet; nor shall any side yard adjoining a street be less than 10 feet; nor shall any rear yard be less than 10 feet; and the front yard shall be as required in Schedule I of this chapter.