24 CFR § 40.2 - Definition of “residential structure”.
(1) Constructed or altered by or on behalf of the United States;
(2) Leased in whole or in part by the United States after August 12, 1968, if constructed or altered in accordance with plans and specifications of the United States; or
(3) Financed in whole or in part by a grant or loan made by the United States after August 12, 1968, if such residential structure is subject to standards for design, construction, or alteration issued under authority of the law authorizing such grant or loan.
(b) As used in this part, residential structure includes the following:
(1) Any residential structure which, in whole or in part, is intended for occupancy by the physically handicapped or designed for occupancy by the elderly;
(2) All elevator residential structures;
(3) Any residential structure that contains 15 or more housing units, unless otherwise specifically prescribed by the Uniform Federal Accessibility Standards.