5.__Sand and water movement.__To allow for the movement of sand and water and future shoreline changes, all buildings modified or reconstructed pursuant to subsection 2, paragraph D or subsection 4, except for detached buildings that are used as storage sheds, public bathhouses and garages, must have the lowest portion of the structural members of the lowest floor constructed on a post or piling foundation, and be elevated either:

A.__Three feet above the highest existing elevation within the building's footprint or the highest natural elevation measured 5 feet from the corners of the existing building foundation; or

B.__To the elevation required in the local municipal floodplain ordinance, whichever is greater.

The post or piling foundation may be enclosed with latticework or similar material through which water, wind and sand can easily move.

§480-CC.__Standards for back dune projects

1.__General standards.__Each back dune project must meet the standards for all projects listed in section 480-AA.

2.__Development on individual lots.__No more than 20% of the total area of a lot may be covered by buildings.__If building coverage exceeds 20% of the total area on the date an application is accepted for processing by the department pursuant to section 480-AA, subsection 1, or did exceed 20% of the total lot area within one year of the date that an application is accepted for processing by the department, the percentage of area covered by buildings may not be increased.

3.__Unstable back dune areas.__Certain back dune areas may be identified by the department as erosion hazard areas.__New buildings, additions to existing buildings and reconstructed buildings located in those areas must meet the standards of section 480-BB, subsection 5.

§480-DD.__Variances

1.__Variance.__The department may grant a variance from section 480-AA, subsection 2, paragraph C and 480-BB, subsections 2 and 3 in whole or in part for the construction of a building on a previously undeveloped lot under single ownership.