Problem is cupping. House is surrounded by water on Chesapeake Bay. Builder installed insulation between joist and a layer of black plastic attached to joist in craw space. Ground is covered w/ wet gravel...real wet. Should black plastic be removed from joist & new layer be put over stones then taped w/ Tyvek tape? Would the existing black plastic be trapping moisture just below subfloor causing the floor to cup. Surface moisture on finished floor is 9-12%. Moisture reading on top plate of foundation wall is 20%. It seems to me that if we allow air to travel thru the foundation vents and we place the vapor barrier on the ground so the joist & subflooring can breath maybe I can go w/ an engineered floor....Ofcourse after we prove the subfloor moisture is around 10% or less!! Just fishing..any ideas?

I suggest going to the NWFACP website, and find an inspector in your region.

The moisture barrier should have been installed over the gravel and run up the perimeter walla a bit to ensure total coverage. Adding proper ventilation on opposite walls in the direction of prevailing winds is also a requirement, not an option.