The area of the lot shall be not less than 5,000 square feet, and the width of the lot shall be not less than 50 feet at the building line.

On a lot used exclusively for a commercial purpose, not more than 70% of the area of the lot may be occupied by buildings, and there shall be the following yards on such lot: a front yard of not less than 10 feet in depth and a rear yard of not less than 15 feet in depth, but side yards on such lot are not required; provided, however, that on a lot used in part for a commercial purpose and in part for dwelling purposes, there shall be at least one side yard of not less than eight feet in width. On a lot used exclusively for dwelling purposes, the area restrictions and regulations established by this chapter for R-4 Residence Districts shall apply.