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Three sources will tell you three different numbers for the same house. The appraisal district, the listing, and the appraisal are usually all measuring different things under different rules. Here is the one the lender cares about.
Last reviewed August 2026
ANSI Z765-2021 is the American National Standard titled Square Footage, Method for Calculating. It is a published measurement standard: a defined method for deciding what part of a house counts, how it is measured, and how it is reported. It did not originate with the mortgage industry. What changed is that the mortgage industry made it mandatory.
Fannie Mae adopted the standard in its Standardized Property Measuring Guidelines, requiring appraisers to use ANSI Z765-2021 for appraisals with effective dates of April 1, 2022 or later on loans sold to Fannie Mae. Before that, appraisers followed regional custom, and regional custom in North Texas was not identical to regional custom elsewhere. Two competent appraisers could measure the same house honestly and report different numbers because they were applying different conventions. The point of adopting a single standard was to end that.
The standard applies to the kinds of properties most people are buying and selling. Fannie Mae's guidance covers single-family detached dwellings, attached single-family homes, townhomes and rowhouses, manufactured homes and accessory dwelling units. There are defined exceptions, which I cover further down, and the guidance has been updated since it was first published, so check the current fact sheet linked below before relying on any specific detail.
It has to be finished, meaning walls, floor and ceiling are completed in materials consistent with the rest of the house. It has to be heated by a conventional system such as forced air, radiant, solar or ductless. A space heater or a plug-in unit does not qualify. It has to be directly accessible from the rest of the finished area through the interior of the house. And it has to meet the ceiling height rules.
That accessibility rule catches more Fort Worth properties than people expect. A finished bonus room over a detached garage, reachable only by an exterior stair, is finished space. It is not part of the gross living area of the main dwelling. Fannie Mae's guidance describes noncontinuous finished areas, meaning space that is attached but has no interior access, as reported separately and excluded from the primary finished area count. Same principle for a converted porch you have to step outside to reach.
Measurements are taken to the exterior perimeter of the dwelling for detached single-family homes, and recorded to the nearest tenth of a foot, with the final calculation reported to the nearest whole square foot. Apartment-style condominium units are the exception and are measured to the interior perimeter, which is why a condominium's reported area is usually smaller than a comparable detached footprint.
This is the rule that causes the most argument, and it is also the least negotiable.
Fannie Mae's guidance states that a floor is considered partially or wholly below grade if any portion of its walls is not entirely at or above ground level, and that any space partially or completely below grade is required to be reported as basement area.
Any portion. Not most. Not the majority. If one corner of one wall of that level is below the surrounding ground at any point, the entire level is below grade for reporting purposes, and none of it goes into gross living area.
This is why a walkout basement generates so much frustration. A homeowner in a Fort Worth neighborhood with rolling topography has a lower level with full-height windows, a door to the back yard, finished flooring, heat, and living space that functions exactly like the rest of the house. It is beautiful. It is also below grade, because the front and side walls are cut into the slope, and under the standard it is reported as below-grade area regardless of how it lives.
That is a reporting rule, not a statement that the space is worthless. Fannie Mae's guidance is explicit that areas not counted in gross living area are reported on a separate line in the sales comparison grid with a market adjustment applied. So the finished lower level is measured, described and analyzed, and it can contribute meaningfully to the value conclusion. What it cannot do is get added to the above-grade square footage. If buyers in that market pay for finished lower level space, the analysis is supposed to capture that on its own line.
For flat ceilings the rule is simple. Finished area needs a ceiling height of at least seven feet to be included.
Sloped ceilings get a two-part test, and both parts have to pass. At least 50 percent of the finished square footage of the room must have a ceiling height of at least seven feet, and no portion of the room with a ceiling height under five feet can be included at all.
Fannie Mae's guidance addresses the leftover case as well: space that is finished but does not meet the height standards is reported separately as nonstandard finished area rather than simply ignored. Again, described and analyzed, but not folded into gross living area.
Two related details. Openings to the floor below, meaning a two-story foyer or an open stairwell void, are not included in the reported square footage, because there is no floor there to count. And staircases are included in the square footage of the floor from which they descend, so a stair from the second floor to the first counts once, on the second floor.
Garages are not finished square footage. Not attached, not oversized, not finished out with drywall and epoxy floors. Under the standard, garage space is excluded from gross living area.
A converted garage is a different question, and the answer depends on facts rather than intent. If the space has been genuinely converted, meaning it is finished, heated by a conventional system, directly accessible from the interior finished area and meets the ceiling height requirements, it can qualify as finished area. If the garage door is still in place, if it is heated by a window unit, if the floor is still the original sloped slab, or if you have to go outside to get to it, it is not.
Outbuildings are generally not measured under the standard, though accessory dwelling units are covered by the ANSI requirement. A detached workshop, barn or storage building is described and sketched with its dimensions rather than added to the living area of the house.
The requirement is broad but it is not universal, and the exceptions are worth knowing because they explain some apparent inconsistencies.
Fannie Mae's guidance identifies exceptions including desktop appraisals, two- to four-unit dwellings, apartment-style and multifamily condominium units, which are measured to the interior perimeter instead, and outbuildings other than accessory dwelling units. Manufactured homes are covered by the requirement rather than excepted from it.
There is also a documented path for a property that genuinely cannot be measured to the standard. Fannie Mae's guidance instructs the appraiser who is unable to comply to enter a specific code, GXX001-, at the beginning of the Additional Features field and explain the reason. That is a narrow escape hatch for real physical or access constraints, not a convenience, and it puts the explanation on the record.
The other thing the guidance settles is the local custom argument. When ANSI conflicts with how a market has historically measured, the appraiser must measure and report the subject's gross living area following the ANSI standard. Local practice does not override it.
A county appraisal district performs mass appraisal. Its job is to value hundreds of thousands of properties annually for ad valorem taxation, using models applied at scale. Its square footage records are typically built from a combination of building permits, builder or developer plans filed at construction, prior field data, and periodic exterior review. A district is not sending someone inside your house every year with a laser measure, and it is not applying ANSI Z765-2021, because it is not performing a mortgage appraisal for a loan sold to Fannie Mae.
That produces predictable and recurring divergences. A permitted addition may be recorded from the plan rather than as built. An attic or garage conversion may be recorded as finished area without the ceiling height or access test ever being applied. A finished lower level may sit in the total living area rather than being separated as below grade. An enclosed patio may or may not have been picked up. Records carry forward through ownership changes for decades without being re-verified. None of this is malfeasance. It is the arithmetic of valuing an entire county with limited resources.
So when the appraisal comes back with a different number, the useful question is not who is wrong. It is which spaces are being counted differently, and why. Nearly every time I have walked through a discrepancy with a homeowner in Tarrant County, it resolves to one of a handful of causes: a below-grade level, a converted space that fails the access or height test, an area under a sloped ceiling, a two-story opening being counted twice somewhere, or a stale record that was never updated after a change to the house.
If your county record and your actual house have drifted apart, you generally want to find that out before a buyer's appraiser does, not after a contract is signed and a closing date is on the calendar.
One caution I will repeat. Square footage is one variable among many. It is a significant one, but a change in reported area does not translate into a proportional change in value, and I will not suggest otherwise. Location, site, condition, quality, functional layout and what comparable properties actually sold for all carry weight. Anyone who tells you what a corrected measurement will do to your value is guessing.
Last reviewed August 2026. Fannie Mae's measurement guidance has been revised since its original publication and the reporting environment is changing with the UAD 3.6 transition. Verify current requirements against the sources below.
Fannie Mae requires appraisers to use the ANSI Z765-2021 measuring standard for appraisals with effective dates of April 1, 2022 or later on loans sold to Fannie Mae, subject to stated exceptions including desktop appraisals, two- to four-unit dwellings and apartment-style condominium units.
A floor is partially or wholly below grade if any portion of its walls is not entirely at or above ground level, and that space must be reported as basement area. A walkout basement with full windows and a back door is still below grade. It is reported and analyzed on its own line, not added to above-grade living area.
The county appraisal district performs mass appraisal for taxation and does not apply ANSI Z765-2021. When the numbers disagree, the two sources are usually counting different spaces under different rules rather than one of them being wrong.
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Because of how the standard defines grade. A floor is treated as partially or wholly below grade if any portion of its walls is not entirely at or above ground level, and Fannie Mae requires that space to be reported as basement area. It is still measured, described and analyzed on a separate line in the sales comparison grid with a market adjustment, but it is not gross living area.
No. The test is whether any portion of the walls of that floor is below ground level, not whether part of it opens at grade. If the level is cut into a slope on any side, it is reported as below-grade area even though it may function and finish exactly like the rest of the house.
No. Garage space is excluded from gross living area under the standard, regardless of how it is finished. A garage that has been genuinely converted may qualify if it is finished, heated by a conventional system, directly accessible from the interior finished area and meets the ceiling height requirements.
Two conditions apply together. At least 50 percent of the finished square footage of the room must have a ceiling height of at least seven feet, and no portion under five feet may be included at all. Finished space that fails those tests is reported separately as nonstandard finished area rather than as gross living area.
Yes, once. Staircases are included in the square footage of the floor from which they descend. Related to that, openings to the floor below, such as a two-story foyer or an open stairwell void, are not included in the reported square footage because there is no floor area there to count.
Usually both, for their own purposes. The district performs mass appraisal for taxation using permits, plans and periodic review, and does not apply ANSI Z765-2021. The mortgage appraisal applies the standard. The differences almost always trace to a below-grade level, a converted space that fails an access or height test, area under a sloped ceiling, a two-story opening, or a county record that was never updated.
No. Fannie Mae's guidance identifies exceptions including desktop appraisals, two- to four-unit dwellings, apartment-style and multifamily condominium units, which are measured to the interior perimeter, and outbuildings other than accessory dwelling units. Manufactured homes are covered by the requirement. There is also a documented code an appraiser enters when compliance is genuinely not possible, along with an explanation.
I cannot tell you that, and nobody honestly can. Square footage is one significant variable among many, alongside location, site, condition, quality, layout and verified comparable sales. A correction to the reported area does not translate into a proportional change in value.
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