§42-297.
Nonconforming Structures Containing Nonconforming Uses
  A.
Improvement or Alteration of a Structure. Where a nonconforming structure contains a 
nonconforming
use, no improvement or alteration of the nonconforming structure is permitted
except where such
improvement or alteration: 
(1)
Does not result in an expansion/enlargement of the structure
(2)
Is required by law or order from the Zoning Administrator, Building Inspector or Fire 
Marshal to ensure safety of the structure; or 
(3)
Is on a residential structure (where such alteration may occur provided that no additional  
dwelling units result, and that the alteration complies with the requirements for residential
structures of the applicable district).
      B.
Nonconforming Use. Standards for nonconforming uses shall also apply (see §42-298 
-
Nonconforming Uses).
C.
Enlargement or Expansion of a Use. A nonconforming use of a structure may be enlarged or
expanded only into portions of the structure which existed at the time the use became 
nonconforming.