Significantly altered definition
Significantly altered and "significant alteration" shall mean the reconstruction, remodeling or rehabilitation of, or other physical changes to, a structure or building, or a portion thereof, over any two-year period, whether or not involving any supporting members of the structure or building and whether altering interior or exterior components of the structure or building, which involves expenditures amounting to 33 1/3 percent or more of the market value of the structure or building, or portion thereof, at the time of the application for an alteration permit.
Significantly altered means to be modified, changed, improved, reconstructed, defaced, vandalized, or damaged in any manner that is not considered ordinary repairs, maintenance, or renovations and is inconsistent with the U.S. Secretary of the Interior’s Standards for the Treatment of Historic Properties, 36 C.F.R. 68.