In an R-1 zone, the lot area per family shall not be less than nine thousand square feet, except that the lot area for approved two-family corner lots and common wall, single-family corner lots shall not be less than nine thousand square feet for two families. This requirement does not apply to accessory dwelling units. (Ord. 4796 §1(b), 2003; Ord. 4128 (part), 1981; Ord. 3380 (part), 1968).