In April, 1996 the American National Standards Institute (ANSI) adopted a standard for measuring single-family residential buildings. American National Standard Z765-1996 was developed through a process of consensus among a wide variety of participants. These included the American Institute of Architects, the Appraisal Foundation, the Building Owners and Managers Association, the Manufactured Housing Institute, the National Association of Realtors, Fannie Mae, Freddie Mac,HUD and others. It is still in widespread use today.
The ANSI standards are not law, only a voluntary guide, and are subject to periodic review and revision. But anyone using these standards must apply them as a whole, and not just pick out the parts they like or agree with. The standards are intended for both attached and detached single family residences, but not for apartments or multi-family residences.
The ANSI standards base floor area calculations on the exterior dimensions of thebuilding at each floor level, and include all interior walls and voids. For attached units, the outside dimension is the center line of the common walls. Internal room dimensions aren’t used in this system of measuring.
The ANSI standards define “finished area” as “an enclosed area in a house suitable for year-round use, embodying walls, floors, and ceilings that are similar to the rest of the house.” Measurements must be taken to the nearest inch or tenth of a foot, and floor area must be reported to the nearest square foot. Garages are specifically excluded.
Also excluded are any areas, such as porches and converted garages, which are not finished or heated the same as the rest of the house.