Do stairs count as square footage?

Yes. Under ANSI Z765 stairs count as part of the floor they go down from, like the rest of that floor.

Short answer

Yes

On the floor they go down from. Upper floor with stairs · counts, open to below · separately.

By the Squaremetry team · Checked September 27, 2026 · 2 min read · How we calculate

Short answer

Yes, on the floor they go down from.

Yes. Under ANSI Z765 stairs count as part of the floor they go down from, like the rest of that floor.

Stairs are finished space inside the home. Counting them once, on the floor they start from going down, keeps them from being counted twice.

Stairs to a basement: They count on the floor above, because the basement itself is below grade.
Open to below: A two-storey space counts only on the lower floor, not again upstairs.
Outdoor steps: Steps outside the house never count.

Figure 1. Upper floor with stairs: 900 sq ft counts. Open to below: 60 sq ft is shown on its own line.

Area	Sq ft	Under ANSI Z765
Upper floor with stairs	900	Counts toward the GLA
Open to below	60	Reported separately

Good to know

Draw the stairwell as part of the upper floor, not as its own room.

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.