16 U.S. Code § 251h - Property retention rights; compensation at fair market value; “improved property” defined
(1) Any owner or owners of improved property within the boundaries of the park, as revised by and pursuant to sections 251e to 251m of this title may, on the date of its acquisition, retain for themselves and their successors or assigns a right of use and occupancy of the property for such noncommercial residential purposes as existed on or before January 1, 1976, for twenty-five years, or, in lieu thereof, for a term ending at the death of the owner or his spouse, whichever is later. The Secretary shall pay to the owner the fair market value of the property on the date of such acquisition, less the fair market value on such date of the right retained by the owner.
(2) As used in sections 251e to 251m of this title, the term “improved property” shall mean any single-family dwelling on which construction was begun before January 1, 1976, together with so much of the land on which the dwelling is situated (such land being in the same ownership as the dwelling) as shall be reasonably necessary for the enjoyment of the dwelling for the sole purpose of noncommercial residential use, as the Secretary shall designate. The amount of the land so designated shall in every case be not more than three acres in area: Provided, That the Secretary may exclude from the land so designated any beach or water, together with so much of the land adjoining any such beach or water, as he may deem necessary for public access thereto.