Variations and exceptions from the design and dimensional standards and improvement requirements of these regulations may be made by the real estate development board in cases where, owing to exceptional conditions, there are extreme difficulties or hardships in the way of carrying out the strict letter of these regulations. Resubdivision of a single lot of a platted block of an old subdivision shall be considered as an exceptional condition meriting departure from the strict letter of these regulations. No variation or exception shall be made that will be detrimental to the public welfare. (1970 Code §35.28)