My house is 1760 sqft. My unfinished basement is 1800 sqft (including cold storage). I use 1300 sqft of the basement as my store. It is my full time job for many years. I allow walk-in traffic. It has its own walkway and entrance. I had heard in the past that unfinished can't be claimed since it's not "actual" square footage of the residence, but I recently read a comment that it could be claimed. It was just a comment, so I would like to know for sure either way. Thank you.
