Joining Mortgage via Co-Mortgage

[Tyler D.]

This is likely an over-engineering some more simple transaction, but thinking aloud here. My mom has a considerable amount of equity tied up in her house and it makes sense for her to unlock some of that cash now to take care of a modest amount of other higher interest debt. Given the current low-rate rate environment, and my high income, I'm wondering if, through a refinancing, I can invest a specific dollar amount into the equity of the home, reduce the interest rate by my joining the mortgage (significant increase in income) and my mom receive the proceeds of that investment. The house will likely be sold in the next several years, at which time I would receive cash inclusive of equity created by mortgage payments between now and that time. Is something like this feasible from 1) the lender's perspective and 2) a tax perspective? 

A simpler solution may be to make a gift (as defined by IRS) or no- or low-interest loan, but this way loan is backed by house and my mom is able to capitalize on lower rates for the mortgage.