FAQ · 6 min read

Finished Basement GLA Rules: What Counts Under ANSI Z765?

The short answer: a finished basement never counts as GLA under ANSI Z765 — no matter how finished, livable, or beautiful it is. Below-grade is below-grade. Here is what that means in practice, how appraisers report it, and why the rule exists.

The ANSI Z765 rule on below-grade space

ANSI Z765-2021 — the standard that governs how residential appraisers calculate Gross Living Area — is explicit: below-grade space is excluded from GLA. A space is considered below grade if any portion of its floor level is below the exterior grade line, even on just one wall.

This applies regardless of:

• How finished the basement is (full kitchen, full bath, luxury flooring — doesn't matter)
• Whether it has direct walkout access to grade level
• Whether windows let in natural light
• Whether it has a separate entrance or is used as a rental unit
• What the MLS or county assessor shows

If the floor is at or below grade on any side, the space is below grade, and it cannot be part of GLA.

The walkout basement question

Walkout basements cause the most confusion. A walkout basement has at least one wall fully above grade — often with sliding doors and full windows opening directly to a patio or backyard. Buyers frequently perceive this space as equivalent to above-grade living area.

Under ANSI Z765, a walkout basement is still below grade if any portion of the floor is below grade on any wall. The fact that one side walks out does not elevate the other three walls above ground.

The standard requires that the entire level be above grade to count as GLA. A basement that drops below grade on the front of the house is below grade — period.

How appraisers report finished basement area

A finished basement is not ignored — it is just reported separately. On a standard URAR form, appraisers use the basement and finished area section to document:

• Total basement square footage (finished and unfinished)
• Square footage of finished below-grade area
• What rooms or features are finished (bath, bedroom, rec room, etc.)

Comparables are adjusted for finished below-grade area, similar to how adjustments are made for garage space, decks, or other contributory features. The finished basement adds value — it just is not part of the GLA calculation used for comp selection and size adjustments.

A home with 1,800 sq ft of above-grade GLA and 900 sq ft of finished walkout basement is a very different property than a 1,800 sq ft home with no basement — but the GLA figure on the appraisal report will read 1,800 sq ft in both cases. The appraiser accounts for the basement through a separate line item adjustment.

Why MLS and assessor records often disagree

This is the most common source of “your appraisal came in lower than expected” surprises. Agents frequently list a home's total square footage including the finished basement, because that's what buyers experience when they walk through. County assessors may use their own methodology — sometimes counting finished below-grade area for tax purposes.

Neither is necessarily wrong — they are measuring different things. The appraisal standard (ANSI Z765) defines GLA as above-grade only, which is more conservative and creates the gap buyers sometimes see between listed square footage and appraised square footage.

Measuring a finished basement with PlanSnapper

PlanSnapper handles multi-level floor plans. When measuring a property with a finished basement:

• Measure each level separately. Upload the basement floor plan and trace it as a separate polygon from the above-grade floors.
• Label each polygon. Use the label tool to mark one polygon as “Above Grade” and another as “Below Grade / Basement.”
• Report separately. PlanSnapper will show square footage for each polygon. Use the above-grade total as your GLA and the basement total as your finished below-grade area for the appraisal form.

If you have a CubiCasa, iGUIDE, or Matterport floor plan, the individual level exports make this straightforward — each level is a separate image or PDF page.

Quick reference: finished basement GLA checklist

• Floor below grade on any wall? → Exclude from GLA
• Walkout with three below-grade walls? → Exclude from GLA
• Fully above grade on all sides? → Include in GLA (if finished and heated)
• Finished below-grade area? → Report separately as below-grade finished area
• MLS includes basement in sq ft? → Do not use as GLA — verify with assessor record and your own measurement