Short answer
Short answer
Only the finished part, and only where it is high enough.
Only a finished attic counts, and only the part with a ceiling of at least 5 ft. At least half of the finished space must be 7 ft or higher.
Why
Under ANSI Z765, parts of a room lower than 5 ft never count. A floor with a sloped ceiling counts only when at least half of it is 7 ft or higher; otherwise it is reported on its own line.
Exceptions
- Unfinished attics
- Storage space with bare rafters or insulation does not count.
- Low knee walls
- The strip under 5 ft is left out, even inside a finished room.
- Dormers
- A dormer can lift enough of the floor above 7 ft to make the room count.
Example
Figure 1. Finished, 5 ft and higher: 380 sq ft counts. Under 5 ft: 170 sq ft is shown on its own line.
| Area | Sq ft | Under ANSI Z765 |
|---|---|---|
| Finished, 5 ft and higher | 380 | Counts toward the GLA |
| Under 5 ft | 170 | Reported separately |
Good to know
Measure where the ceiling is 5 ft and 7 ft high, and note both lines on your sketch.
Source and version
The rule comes from ANSI Z765-2021, Square Footage: Method for Calculating (Home Innovation Research Labs), in our own words. Source checked on September 24, 2026; this page checked on September 27, 2026.