72.29.1. 
The provisions of this ordinance do not require any changes or improvements to be made to lawfully existing structures. However, when an improvement is made to any existing structure, the provisions of Section 72.30 shall apply.
72.30.1. 
The following provisions shall apply whenever any improvement is made to an existing structure located within any identified floodplain area:
1. 
No construction, development, use or activity shall be permitted within any identified floodway.
2. 
No expansion or enlargement of an existing structure shall be allowed within any identified floodplain area outside the floodway that would, together with all other existing and anticipated development, increase the base flood elevation.
3. 
Any modification, alteration, reconstruction, or improvement of any kind to an existing structure, to an extent or amount of 50% or more of its market value, shall constitute a substantial improvement and shall be undertaken only in full compliance with the provisions of this ordinance.
4. 
Any modification, alteration, reconstruction, or improvement of any kind to an existing structure, to an extent or amount of less than 50% of its market value, shall be elevated and/or floodproofed to the greatest extent possible.