26 CFR §1.274-7

If deductions are disallowed under § 1.274-2 with respect to any portion of a facility, such portion shall be treated as an asset which is used for personal, living, and family purposes (and not as an asset used in a trade or business). Thus, the basis of such a facility will be adjusted for purposes of computing depreciation deductions and determining gain or loss on the sale of such facility in the same manner as other property (for example, a residence) which is regarded as used partly for business and partly for personal purposes.