This does not conform to my understanding of the problem.
Get a refinance mortgage for $200,000. Use 100,000 to pay off the prior loan and use 50,000 to fix the foundation and use 50,000 to do non-house things... Now 75% of the mortgage is deductible and 25% is not. Right?... 1 year passes. There have been no changes in the expenses paid out of the mortgage loan. The money is all allocated back in year one. So the 75% is still the applicable rate on whatever the interest expense was for the year.... another year passes. No new expenses against the mortgage because the money is long gone. The percentage calculation remains the same because it was about the use of money back in year 0 when the funds were received and the contract began. No?
Re-finding the records of the expenses from an ever-receding year to recalculate the ratio of house to non-house uses for funds over and over is not a good work plan. Better would be to hold that information in the worksheets, bring them forward year to year like the donation history and the various schedules and review them from there. Often I find that I am being conscripted at my cost to be a QA engineer for Intuit.
