"Open space" means the portion of ground level area of a lot which is unobstructed from the ground level upwards and which meets the following criteria:
A. Its minimum dimensions are fifteen feet by fifteen feet;
B. At least fifty percent of such area is in lawns, live plantings, and other permeable ground cover;
C. No more than fifty percent of such area is covered by paving for sidewalks, leisure and recreational areas such as patios, tennis courts, and swimming pools;
D. No part of such area is used for parking, drives, or loading areas.
(Ord. 81-11 Art. II (part), 1980).