The Middle Tennessee Regional Multiple Listing Service requires that homes be measured and square footage reported in accordance with the American National Standards Institute Standard Z765-2003.  

According to the ANSI voluntary Standard Z765-2003…

Finished Area

Finished area is defined as "an enclosed area in a house at is suitable for year round use, embodying walls, floors, and ceiling that are similar to the rest of the house."  Furthermore, "above-grade finished square footage of a house is the sum of the areas on levels that are entirely above grade.  The below-grade finished square footage of a house is the sum of the areas on levels that are wholly or partly below grade."

Suitable for year round living requires permanently installed heat with a continuous power source (electricity, natural gas, permanently installed propane tank, or heating oil).  Through-the-wall heating units and permanently installed baseboard heaters meet the requirement, but window units and portable space heaters do not.

The walls and ceiling must be finished.  The floors must be completely covered with an installed covering (carpet, vinyl, wood, tile, laminate or stamped or stained concrete).  Exposed or painted concrete, or exposed or painted plywood is not considered a finished floor.

The finished space must be contiguous and directly accessible from the balance of the living area.  Finished space that lack permanent stairs or direct access, such as plant shelves, are not considered living area.  Finished spaces only accessed by ladders, such as lofts, are not considered living area.

Stairs and landing are included on each level.  Stairways are included in the level from which they decent even if they are unfinished and/or unheated.

Attics, Lofts and Low Ceilings

Level ceilings must be at least 7 feet high, and at least 6 feet 4 inches under beams, ducts and other obstructions. There is no height restriction under stairs. If a room has a sloped ceiling, at least one-half of the finished floor area must have a ceiling height of at least 7 feet. Otherwise, omit the entire room from the floor area calculations. If a room with a sloped ceiling meets the one-half-of- floor-area-over-7-feet requirement, then include all the floor space with a ceiling height over 5 feet.

Lofts and finished attics must be accessible by a conventional stairway or other access to be counted. If you can only reach the loft by climbing a ladder, it’s not part of the finished floor area regardless of the ceiling height.

Open Areas

Many recently constructed homes offer two story foyers and other areas with lofted and/or two story ceilings.  While these areas are finished and are heated space, they lack floors on the upper level and are, therefore, excluded for the calculation of gross living area on the level which is open.  However, stairways and landing are included on each level.  If you can not walk on it, it does not count. 

Below-Grade/Basement Space

Why is basement or below-grade space considered separately from above grade space? There are several reasons and in each case some or all of these may apply.

1. Below grade space is typically on slab which is less comfortable to walk on compared to the home’s wood frame above grade space. 
2. There is often less natural light with below grade space. Additionally, finished rooms below-grade often have no direct exterior egress, or the exterior egress is not readily accessible. 
3. While below-grade space is measured from the exterior, like above-grade space. There is less usable space because the exterior walls are thicker. An above grade wall has the veneer, sheaving, stud walls and drywall, while a below grade wall has the concrete block or poured concrete of the foundation wall, plus the stud wall and drywall or paneling, or just painted concrete block.
4. Buyers are apprehensive that at sometime in the future there will be water penetration into below-grade space.