Regulation Z generally exempts all “residential mortgage transactions” from its requirements, including the right of rescission. 12 CFR 1026.15(f)1026.23(f). The term “residential mortgage transaction” is defined as “a transaction in which a mortgage, deed of trust, purchase money security interest arising under an installment sales contract, or equivalent consensual security interest is created or retained in the consumer’s principal dwelling to finance the acquisition or initial construction of that dwelling.” 12 CFR 1026.2(a)(24).