A residential lot existing at the time of passage of this chapter
that is less than the required area or width or that cannot meet the
required front setback for any residential use in the district and
that was owned or under contract for purchase by persons other than
those owning or leasing adjoining lots at the time of adoption of
these regulations may be used for residential purposes, provided that
the lot has a front setback equal to at least 60% of the required
minimum and that minimum side and rear setback requirements can be
met.