In regards to total sq footage if it is finished, i.e. walls, flooring, heated and cooled then it is sq footage. It is not considered living sq footage in tax records which is good as that equals a lower tax bill on the house. Tax records will reflect the square footage of the garage, basement, "living" area in separate sections of the notes.
Regarding the aspect of the appraised value, "If any part of any wall is any distance below grade, the area is not considered in the living area. It's given value independent of living area and is an asset." -Hank
Regarding the aspect of a home owner however, if I can set a couch, chair, TV, etc and hang out there for good amount of time it is livable square footage.... more