Robin is correct - However, a little more clarification to her answer.
below grade livable usage space such as basements, finished or not, will not be included in the GLA (Gross Livable Area) square footage. It will however be included in the value conclusion but not valued the same ($ per sq ft for example) as the above grade, or GLA portion. Generally speaking, a lesser value more equivalent to storage space. The same also applies for attics which are used as living space.