Understanding ANSI Square Footage Standards and Their Impact on Real Estate Appraisals

As a professional real estate appraiser, I want to address an important change that is shaping how square footage is measured and reported in residential real estate.

In April 2022 FannieMae adopted the ANSI Standard (American National Standards Institute) square footage measurement standard for residential single-family homes and mortgages on same sold on the "secondary market".  The appraisal report will identify if ANSI was used or not depending on the client and use of the report.   

This page will clarify the confusion surrounding square footage reporting, especially in Miami-Dade County. The Miami-Dade Property Appraiser's (PA) website provides three different square footage indicators, which can create discrepancies when comparing public records to MLS listings.  They are as follows: 

                   Actual Area
                   Living Area
                   Adjusted Area

The Realtors' Multiple Listing System (MLS) commonly displays "adjusted" square footage rather than the "air-conditioned" living area, the primary focus under the ANSI standard. Both may appear in a Realtor's MLS listing.  The adjusted area is used by the county for taxation of "just value".   As a result, when listings are published on platforms such as Realtor.com, Zillow, and others, the adjusted may be used, and this square footage figure may not accurately reflect the air-conditioned living space required under ANSI.  Realtors can override the square footage reporting by submitting their own documentation to the Miami Association of Realtors (MAR) for review and inclusion in the MLS.  

This article will  also help explain terminology, ANSI square footage measuring requirements, detailing what is included in the measurement process, what is considered separate, and how this impacts appraisals. The important discussion on condominium measurements and terminology is located at the bottom of this section. 

Single Family Homes

Square footage in appraisals is often shown in the form as "GLA" or Gross Living Area for appraisals is calculated per ANSI Z765-2021 standards.  While this "GLA" abbreviation aligns with common usage, it is technically a misnomer under the ANSI standard because it is a "net" area (net of garages and overhangs) with measurements taken to the outside wall of the main structure.  Thus, ANSI Z765-2021 requires that measurements be taken to the home's exterior walls. 

Areas such as garages, accessory dwelling units (ADUs), and other non-living spaces are excluded and reported separately.  The link to the documents below specifically indicate that garages and ADU's are not part of the air-conditioned area per ANSI. 

As mentioned above, the Miami-Dade County tax rolls (miamidade.gov) list multiple terms for square footage, including "actual area," "living area," and "adjusted area." These terms are defined as follows:

Actual Area: The total of all measured areas within the property, synonymous with "gross area."

Living Area: Space designated for habitation, typically the air-conditioned (AC area), measured to the exterior walls and excluding accessory dwelling units (ADUs), garages, or overhangs.

Adjusted Area: An internal measure used (by the county) to calculate value, often a combination of AC area and portions of non-living spaces like garages or overhangs.  Adjusted area is a combination of the Living Area or AC area plus a percentage of the garage and overhangs to the Living Area (the percentage can vary based on the PA's findings of quality of the area).  2nd-stories of homes are calculated at 80% of the second level.  This figure may vary and is based on tax assessors' ratings and methodologies.

Measurements for ANSI standards require measurements taken to the tenth-of-an-inch or decimal.  Discrepancies between county-reported areas and on-site measurements are common. For example, Miami-Dade tax records often list only the "adjusted" area, which may not align with ANSI-defined GLA. Information in the Realtor’s MLS often mirrors these tax records but the Realtor can also override the system and include additional details about square footage. 

As the purpose of the appraisal report it to arrive at a "credible" market value, the sketches included in appraisal report serve as a visualization tool for understanding the property’s size and layout. These sketches are as accurate as possible and usually performed under the ANSI Standard (the report will specify it ANSI is followed or not).  Not all appraisers must follow ANSI when deveoping and writing an appraisal report, and not all appraisals are for loans sold to Fannie on the "secondary market" (the selling of the "paper" to Fannie and other institutional buyers). 

One should read the appraisal report to determine if ANSI standards were applied and if so, the appraiser is required to clearly state it.  However, there may be reasons why a different unit of measurement is used in an appraisal report, if ANSI is not used or followed.  FannieMae guidelines in a non-ANSI reports require only "consistency" in the "unit of measure" and another metric (such as the adjusted area) or unit of measure could be used.  Thus, ANSI is only one square footage standard of measurment that FannieMae adopted for the "secondary market".  It is not always used in each appraisal report, and it depends of the "scope of work" and "intended use" and "user".  There should be an explanation in the addendum to the report for the reader to understand it. 

Even though the standard may be followed, appraisers' measurements are approximate because there is always a small margin of error (estiamted between 2% and 6%) in field measuring.  Thus, buyers and sellers should not rely on appraisal reports alone, nor should third parties and/or Realtors.  Any party requiring precise measurements should independently measure the property and perform their own calculations.  Surveys and architectural plans should also be reviewed for square footage measurements.  On new homes architects usually provide a table or "sheet" with square footage calculations.  If not, the CAD used by architects can generate a sketch with a summary of the areas.  One can instruct the architect of records (if it is recent construciton) to use the exterior walls as the outside broundary and not include the ancillary areas such as garages and ADU's and architects are usually not familar with ANSI and what areas are included and/or excluded in the context of appraisals.  There are also rules for stairways and "atriums" (two story high open areas). 

Often the Miami-Dade County tax rolls (miamidade.gov) reflect a different square footage than found at the subject.  It is beyond the scope of the appraisal assignment typically for the appraiser to check the permit record (and permit records in Miami are not always complete or accurate). If there are discrepancies in what is reported and the total measured, the appraiser will ask questions to attempt to determine the facts. However, often it is not possible and assumptions are made that any floor plan changes to the home were completed with the necessary plans and permits and that "the investigation of this is beyond the "scope of work" of the appraisal report.  Appraisers often make general and "extraordinary" assumptions with the addendums of reports if the information cannot be verified.  FannieMae has guidelines on additions and commentary on it. 

ANSI Documents:
ANSI Fact Sheet
Property Measurement
Understanding ANSI Measurement Standards - Residential Transactions - FannieMae

Condominium Square Footage

Condominium measurements differ greatly from single-family home measurement. Surprisingly, ANSI does not have a specific guidelines for condominiums even though it is one of the more misunderstood areas of square footage measurement. Thus, condominium measurment defaults to FannieMae guidelines as explained below.  

With condominiums, measurments are usually performed in one of two methods:  The GLA or air-conditioned area “AC area” is often stated as the larger "architectural method" for use in developers' promotional brochures.  A second method is the "net" area, or "engineer’s method" with dimensions taken to the inside walls ("paint-to-paint") of the unit. 

Most of the time the Condo Section of the Miami-Dade Property Appriaser (miamidade.gov) will reflect the square footage as listed in the condominium documents, since they are prepared by attorneys and often insclude (engineers) surveys of each unit (required by Florida law). The condo documents in newer buildings more clearly define the areas and  also usually contain individual engineers plans (surveys) of each unit showing the perimeter of the unit (the buidloing shell, also showing the concrete block walls inbetween units.  The sketches usually contain dimensions that are readable, and tables with the "net area" square footages (to determine the pro-rata share).  Note that these scanned documents can be found online at the clerk's office. Since they are scanned at high-speed, the are "not to scale" (nts).

The "architectural method" (builder / developer method) usually contains portions of "common walls", such as the “shear walls” (for structural support)  such as in adjoining “center core” areas, or other areas that are not part of the unit. Dimensions using the architectural method can also be taken to the outside wall and have portions of the "center core" of the common elements in the area. The architectural method is often used with developer’s brochures for use by the public to make comparisons with other developer’s competing projects.

The “engineer’s method” uses the dimensions of the interior walls (painted surface) which is the FannieMae standard.  It is often found in the condominium documents and engineer’s drawings contained in these documents. The condominium documents will also identify interior columns, shear walls, and the elevator lobby.  The more recent condominium documents of the past 10 years are more specific as to defining the aera, and these documents should be consulted to determine what is included and what is excluded.  

As with single family appraisal reports the sketch is typically included in the report to assist the reader in visualizing the floor plan and understanding the appraisers’ determination of its size. However, it should not be relied on by a buyer or seller, or to a third party, because the primary intent of the sketch/floor plans is to determine the approximate size and layout of the property. Any Realtor, buyer, seller or other third party should verify the unit’s square footage and obtain their own measurements and calculations.