I fought ours one year and won because our house was not finished, and comparable houses that were done were assessed less. It was a lot of footwork, but if you are prepared, it can be done. That was upstate NY. When we moved to NC, it was just a matter of walking around with the assessor, and the whole upstairs of our huge Victorian farmhouse was taken off the square footage because it was not ducted for air conditioning. My giant barn was taken off because it did not have a cement floor or foundation. The smoke house was taken off because the supporting piers needed repointing. A lot is in the location and what other places in your area are like.