No single-family dwelling house shall be built on property that has less than 40 feet front, and each house must have a separate lot area of at least 4,000 square feet, and no two-family dwelling house shall be built on property that has less than 50 feet front, and each such house must have a separate lot area of at least 6,000 square feet, and no residence shall be erected in the rear of another residence on the same lot.