What defines a non-conforming structure according to the International Residential Code?

A non-conforming structure is defined as a building that was legally built in accordance with the codes and regulations that were in force at the time of its construction, but now does not meet the current codes and standards. This situation can arise due to changes in the building codes or zoning regulations over time, which can render older buildings non-conforming despite their original lawfulness.

This understanding highlights the nature of non-conformance: it pertains not to the legality of the original construction but to the lack of compliance with updated regulations. The circumstances surrounding changes in codes can often lead to older buildings being assessed differently compared to new constructions, even though they were initially compliant.

Other answer choices do not capture the essence of a non-conforming structure accurately. A building that meets current code requirements is simply compliant, while structures that are in compliance with local authority requirements are also not defined as non-conforming. Furthermore, a structure that has never been inspected for code compliance would not fit the definition, as it does not concern itself with prior lawful construction. Thus, the correct definition focuses on the shift from legal compliance at the time of construction to non-conformance due to updated codes.