26 C.F.R. § 1.1033(b)-1
Example: A's vessel which has an adjusted basis of $100,000 is destroyed in 1950 and A receives in 1951 insurance in the amount of $200,000. If A invests $150,000 in a new vessel, taxable gain to the extent of $50,000 would be recognized. The basis of the new vessel is $100,000; that is, the adjusted basis of the old vessel ($100,000) minus the money received by the taxpayer which was not expended in the acquisition of the new vessel ($50,000) plus the amount of gain recognized upon the conversion ($50,000). If any amount in excess of the proceeds of the conversion is expended in the acquisition of the new property, such amount may be added to the basis otherwise determined.
Example: A taxpayer realizes $22,000 from the involuntary conversion of his barn in 1955; the adjusted basis of the barn to him was $10,000, and he spent in the same year $20,000 for a new barn which resulted in the nonrecognition of $10,000 of the $12,000 gain on the conversion. The basis of the new barn to the taxpayer would be $10,000-the cost of the new barn ($20,000) less the amount of the gain not recognized on the conversion ($10,000). The basis of the new barn would not be a substituted basis in the hands of the taxpayer within the meaning of section 1016(b)(2). If the replacement of the converted barn had been made by the purchase of two smaller barns which, together, were similar or related in service or use to the converted barn and which cost $8,000 and $12,000, respectively, then the basis of the two barns would be $4,000 and $6,000, respectively, the total basis of the purchased property ($10,000) allocated in proportion to their respective costs (8,000/ 20,000 of $10,000 or $4,000; and 12,000/20,000 of $10,000, or $6,000).
26 C.F.R. §1.1033(b)-1