Do stairs count as square footage?
Published August 27, 2026
How it works floor by floor
On a two-story house, the staircase from the second floor to the first is counted with the second floor. On the first floor, the space under the stairs is part of the first floor footprint (it is inside the exterior walls), so it is counted there too. Nothing is double counted because the second-floor opening above the stairs is excluded.
Stairs down to a basement are counted with the first floor, the level they descend from. If the basement is below grade, the stairs are still above-grade area because they belong to the floor above.
Under-stair closets and storage
Finished space under a staircase is counted like any other finished space on that floor. Unfinished under-stair storage in a basement follows the basement.
Frequently asked questions
Are stairs counted on both floors?
No. ANSI counts the treads and landings on the floor they descend from and excludes the opening in the floor above, so the staircase is counted once.