see the worksheet in publication 936 on page 11 ...... it simply asks for the sum of all the debt on the property. Even if the interest rate is zero or the interest is deferred, it's still "debt". Follow the form - pretty easy to do - and the interest that you are able to deduct will be the result
I assume all the 'debt' you are referencing is secured debt of the home. Any debt that is unsecured is not part of the calculation as none of the interest would be deductible in any event.
