43 C.F.R. § 2653.8-2

(a) Periods of occupancy. Casual or occasional use will not be considered as occupancy sufficient to make the tract applied for a primary place of residence.

(b) Improvements constructed on the land. (1) Must have a dwelling.

(2) May include associated structures such as food cellars, drying racks, caches etc.

(c) Evidence of occupancy. Must have evidence of permanent or seasonal occupancy for substantial periods of time.