Structures existing in any identified floodplain area prior to the enactment of this chapter may continue, subject to the following provisions:
A. 
No expansion or enlargement of an existing structure shall be allowed within any identified floodway that would cause any increase in base flood elevation.
B. 
No expansion or enlargement of an existing structure shall be allowed within any special floodplain area that would, together with all other existing and anticipated development, increase the BFE more than one foot at any point.
C. 
Any modification, alteration, reconstruction, or improvement of any kind to an existing structure, the cost of which equals or exceeds 50% of the market value of the structure, either before the improvement or repair is started or, if the structure has been damaged and is being restored, before the damage occurred, shall constitute a substantial improvement and shall be undertaken only in full compliance with the provisions of this chapter. "Substantial improvement" is considered to occur when the first alteration of any wall, ceiling, floor or other structural part of the building commences, whether or not that alteration affects the external dimensions of the structure. The term does not, however, include:
(1) 
Any project for improvement of a structure to comply with existing state or local health, sanitary or safety code specifications which are solely necessary to assure safe living conditions; or
(2) 
Any alteration of a structure listed on the National Register of Historic Places or a state inventory of historic places.
D. 
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.
E. 
Any modification, alteration, reconstruction, or improvement of any kind that meets the definition of "repetitive loss" shall be undertaken only in full compliance with the provisions of this chapter.
F. 
The above activity shall also address the requirements of 34 Pa. Code, as amended, and the 2006 IBC and the 2006 IRC.