The foundation walls are masonry or concrete walls below the ground level that serve as the main support for the frame structure.  If the house has a basement, the foundation walls form the basement.  Unless custom dictates otherwise, the general rule of thumb is that when an agent or appraiser measures a building to compute the gross living area (GLA), only the area above grade level or above the ground is used.  The external dimensions of the building are measured, excluding the garage, porch or patio.  The square footage of foundation related walls or the basement is included in the appraiser’s description of the property.  It has a different square footage calculation than the square footage calculation for above grade level.