iii. For example, where a buyer enters into a written agreement with the creditor holding the seller’s mortgage, allowing the buyer to assume the mortgage, if the buyer had previously purchased the property and agreed with the seller to make the mortgage payments, § (b) does not apply (assumptions involving residential mortgages).

A residential mortgage transaction includes a loan to finance the construction of a consumer’s principal dwelling on a vacant lot previously acquired by the consumer

6. Multiple purpose transactions. For example, a transaction to finance the initial construction of the consumer’s principal dwelling is a residential mortgage transaction even if a portion of the funds will be disbursed directly to the consumer or used to satisfy a loan for the purchase of the land on which the dwelling will be built.

(25) Security interest means an interest in property that secures performance of a consumer credit obligation and that is recognized by State or Federal law. It does not include incidental interests such as interests in proceeds, accessions, additions, fixtures, insurance proceeds (whether or not the creditor is a loss payee or beneficiary), premium rebates, or interests in after-acquired property. For purposes of disclosures under §§ 1026.6, , (e) and (f), and (l)(6), the term does not include an interest that arises solely by operation of law. However, for purposes of the right of rescission under §§  and , the term does include interests that arise solely by operation of law.

1. Threshold test. The threshold test is whether a particular interest in property is recognized as a security interest under applicable law. The regulation does not determine whether a particular interest is a security interest under applicable law. If the creditor is unsure whether a particular interest is a security interest under applicable law (for example, if statutes and case law are either silent or inconclusive on the issue), the creditor may at its option consider such interests as security interests for Truth in Lending purposes. However, the regulation and the commentary do exclude specific interests, such as after-acquired property and accessories, from the scope of the definition regardless of their categorization under applicable law, and these named exclusions may not be disclosed as security interests under the regulation. (But see the discussion of exclusions elsewhere in the commentary to § 1026.2(a)(25).)

A transaction meets the definition of this section if any part of the loan proceeds will be used to finance the acquisition or initial construction of the consumer’s principal dwelling

2. Exclusions. The general definition of security interest excludes three groups of interests: incidental interests, interests in after-acquired property, and interests that arise solely by operation of law. These interests may not be disclosed with the disclosures required under §§ , (e) and (f), and (l)(6), but the creditor is not precluded from preserving these rights elsewhere in the contract documents, or invoking and enforcing such rights, if it is otherwise lawful to do so. If the creditor is unsure whether a particular interest is one of the excluded interests, the creditor may, at its option, consider such interests as security interests for purposes of the Truth in Lending Act (15 U.S.C. 1601 et seq.) and Regulation Z.

ii. The notion of an incidental interest does not encompass an explicit security interest in an insurance policy if that policy is the priple, in an insurance premium financing transaction.

4. Operation of law. Interests that arise solely by operation of law are excluded from the general definition. Also excluded are interests arising by operation of law that are merely repeated or referred to in the contract. However, if the creditor has an interest that arises by operation of law, such as a vendor’s lien, and takes an independent security interest in the same property, such as a UCC security interest, the latter interest is a disclosable security interest unless otherwise provided.