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Measuring the way appraisers do
- Measure exterior dimensions where possible, or interior and add wall thickness consistently.
- Break the space into rectangles and add them.
- Leave out areas with ceilings under 7 ft, except under beams and ducts down to 6 ft 4 in.
- Leave out unfinished rooms such as the furnace room.
- Report the result as finished below-grade area.
The ANSI Z765 standard, which Fannie Mae requires appraisers to use, treats any level that is partly or completely below grade as basement. It is reported as below-grade area, finished or not, and is not part of gross living area. The National Association of Realtors notes that a walk-out basement is still not gross living area, though some markets include finished below-grade space by local custom. Finished areas must also have a ceiling of at least 7 ft to count as finished square footage.
Worked example
The example basement is 32 × 26 ft, 832 sq ft. Leaving out the 120 sq ft furnace room gives 712 sq ft of finished below-grade area. If one 8 × 10 ft section under a sloping stair had a ceiling under 7 ft, another 80 sq ft would come off. None of it becomes above-grade living area.
What appraisers look at in a finished basement
- Whether the space is finished to the same standard as the rest of the house.
- Ceiling height, and whether finished areas reach 7 ft.
- Legal bedrooms with egress openings and a bathroom.
- Walk-out access, which is common in some markets and adds appeal.
- Permits: unpermitted work can be discounted or flagged.
- How comparable recent sales nearby with finished basements were valued.
Exterior or interior measurements?
ANSI Z765 measures finished area from the exterior faces of the walls. Below grade the outside of the wall is buried, so ask how your appraiser measures and use the same method for every rectangle. The number this calculator returns is the figure you would give an appraiser or listing agent as finished below-grade area.
Common questions
How do you calculate basement square footage?
Length × width for each rectangle, added together, minus unfinished areas and areas with ceilings under 7 ft.
Is a basement included in square footage?
Listings may include it in a total, but appraisals under ANSI Z765 report it as below-grade area, separate from gross living area.
Related calculators
Sources
- https://www.mckissock.com/blog/appraisal/understanding-gross-living-area/
- https://www.nar.realtor/node/194378