If the current balance is $100,000 and if you are increasing that to $125,000 then you are adding an additional $25,000 security interest in the property. The additional security interest is subject to rescission.
Addition of a security interest. Under §1026.23(a), the addition of a security interest in a consumer's principal dwelling to an existing obligation is rescindable even if the existing obligation is not satisfied and replaced by a new obligation, and even if the existing obligation was previously exempt under §1026.3(b). The right of rescission applies only to the added security interest, however, and not to the original obligation. In those situations, only the §1026.23(b) notice need be delivered, not new material disclosures; the rescission period will begin to run from the delivery of the notice.
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The opinions expressed are mine and they are not to be taken as legal advice.