you say you owe .5%. what does this mean? if you are a co-signer your liability is the entire mortgage amount.
do you have an ownership interest in the property? in other words, does your name appear on the deed?
to be qualified residence interest the debt must have been incurred to acquire, construct, or substantially improve your main or second home. your ownership % is irrelevant as long as its greater than 0% (REG 1.163-1(b)
