Does a walkout basement count as square footage in Arizona?
No, a walkout basement does not count as square footage in Arizona.
Not as gross living area, in Arizona or any other state. A walkout basement is open to the ground on one side but still buried on the others, and ANSI Z765 puts any level with part of it below ground in the below-grade column. It is reported as finished below-grade area and valued separately, usually higher than a standard basement. Fannie Mae requires that standard everywhere, so the answer does not change at the Arizona line.
Why a walkout basement is not gross living area in Arizona
The walkout side does not rescue the level. ANSI Z765 asks one question: is any part of this floor below the ground on any side? For a walkout the front or side walls are still below grade, so the whole level is below grade. That is why the answer is the same on a sloped lot in Arizona as on a flat one. The one exception is a lower level that sits entirely above ground on every side, which is a fact about the lot, not the design.
Where a walkout does differ is value. Full-height windows, a door at grade, and a patio make the space feel like a lower level, and in markets where buyers pay close to above-grade prices for it, the appraiser supports a larger below-grade adjustment. The square footage still sits on the below-grade line.
Basements in Arizona homes: the numbers
Basements are rare in Arizona. Only 3% of single-family homes in the state sit over one, against 43% nationwide, according to the 2024 Residential Energy Consumption Survey. Most Arizona houses are built on a slab or a crawl space, so the question comes up mostly with older homes, hillside lots, and houses bought in other states.
Of those basements, 82% are finished. Every square foot of that finished area is measured by an appraiser and reported as below-grade finished area, never as gross living area.
Here is the number that explains the arguments: 31% of Arizona owners with a basement include it when they report their home's square footage. Nationally it is 40%. Under ANSI Z765, none of them should, which is why an owner's number and an appraiser's number so often disagree.
The average Arizona single-family home has 2,086 square feet of total area, basement included, compared with 2,248 nationally.
| Single-family homes | Arizona (2024) | United States (2024) |
|---|---|---|
| Have a basement | 3% | 43% |
| Basements that are finished | 82% | 59% |
| Owners who count the basement in their square footage | 31% | 40% |
| Average total area, basement included | 2,086 sq ft | 2,248 sq ft |
Source: U.S. Energy Information Administration, Residential Energy Consumption Survey. Values are for single-family homes; a small number of states have samples too small to report every line.
Calculator: what a walkout basement adds to a Arizona house
Enter the walkout basement area and the above-grade area. The first figure is the gross living area an appraiser reports; the last is the inflated number a listing shows when it adds the basement in.
The walkout basement does not count. The appraisal GLA stays at 1,800 square feet. A listing that adds it in would show 2,600, which overstates the house by 44%.
How West basements changed since 1971
Arizona is in the Census Bureau's West region. In 1971, 15% of new single-family houses completed in the West were built with a full or partial basement. In 2025 it was 16%. Nationally the share went from 36% to 16% over the same years, as slab and crawl-space construction spread.
What to put on a Arizona listing
Report the above-grade area as the square footage and the walkout basement on the below-grade or "finished basement" line your MLS provides. Most Arizona listing systems have separate fields for above-grade, below-grade, and total finished area. Filling in the total field is fine; presenting it as the size of the house is what causes appraisal gaps and, in some states, complaints.
If a buyer's appraisal comes in with a smaller number than the listing, this is almost always the reason. The house did not shrink. The basement moved to the line where ANSI Z765 puts it.
Frequently asked questions
Does a walkout basement add to square footage in Arizona?
It adds value and it adds below-grade finished area, but it does not add to gross living area. Arizona appraisers follow ANSI Z765 because Fannie Mae requires it, and that standard keeps every basement on a separate line.
Do Arizona appraisers count a walkout basement?
They measure it, report it as below-grade area, and value it with its own adjustment. They do not count it in GLA. There is no Arizona exception to the standard.
Does Zillow square footage include the basement in Arizona?
Often, yes. Zillow and county records frequently show a total that includes finished basement area, and 31% of Arizona owners with a basement count it in their own figure. An appraisal will show a smaller number because it reports above-grade GLA only.