American's with Disabilities Act (Specifiacally Title III- Public Accomodations-and commercial facilities) no individual may be discriminated against on the basis of disability with regards to the full and equal enjoyment of the goods, services, facilities, or accommodations of any place of public accommodation by any person who owns, leases (or leases to), or operates a place of public accommodation. Title III also has application to existing facilities. One of the definitions of "discrimination" under Title III of the ADA is a "failure to remove" architectural barriers in existing facilities.
There are exceptions to this title; many private clubs and religious organizations may not be bound by Title III. With regard to historic properties (those properties that are listed or that are eligible for listing in the National Register of Historic Places, or properties designated as historic under State or local law), those facilities must still comply with the provisions of Title III of the ADA to the "maximum extent feasible" but if following the usual standards would "threaten to destroy the historic significance of a feature of the building" then alternative standards may be used.
This means (in my mind) that seeing that the GM is a historic Tilt house that only a handful of these are remaining in the US, this structure does not need to comply due to the age, and significance of the stucture as it would destroy the significance of the structure. This means that if it WERE damaged, then it would, by law HAVE to comply with the standards of ADA leaving the tilt house a thing of the past.
