Whenever a building or use constructed or established after February 10, 1969, is changed or enlarged in floor area, number of employees, number of dwelling units, seating capacity or otherwise, parking spaces shall be provided on the basis of the enlargement or change. Whenever a building or use existing prior to February 10, 1969, is reconstructed or is enlarged to the extent of twenty percent (20%) or more in floor area, said building or use in its entirety shall then and thereafter comply with the parking requirements set forth herein. Any enlargement or change in use of less than twenty percent (20%) of the gross floor area shall be provided with parking based on the enlargement or change.