In order to be deductible the loan must be on a Qualified Home.
Here is the definition of a Qualified Home from IRS Publication 936:Qualified Home
For you to take a home mortgage interest deduction, your debt must be secured by a qualified home. This means your main home or your second home. A home includes a house, condominium, cooperative, mobile home, house trailer, boat, or similar property that has sleeping, cooking, and toilet facilities.