Do Stairs Count as Square Footage?
Yes. A staircase counts as finished square footage, and here's the part that surprises almost everyone: it gets counted twice. Under the ANSI Z765 standard that appraisers use, the stairs are included in the finished area of the floor they descend from, and the floor space underneath them is counted again on the level below. So a staircase connecting two stories effectively shows up on both stories. That isn't a loophole or a mistake. It falls straight out of how the standard measures a house, and once you see the logic it makes sense.
The one-sentence rule appraisers follow
The ANSI Z765 standard that Fannie Mae and Freddie Mac require on most appraisals puts it plainly: stairs are counted as part of the level from which they descend, and the area under the stairs is counted as part of the lower level, regardless of the ceiling height or finish beneath them.
Read that twice, because both halves matter. "The level from which they descend" is the top of the flight. If a staircase runs from your second floor down to your first floor, ANSI treats those treads and the landing as part of the second-floor area, because that is where the stairs start their descent. Meanwhile, the actual floor beneath the staircase, the triangle of space under the steps, belongs to the first floor. The appraiser measures the first floor's full exterior footprint, and that footprint already includes the ground the staircase sits on top of. Add those two facts together and the staircase footprint lands in the count on both levels.
Why counting it twice is correct, not a glitch
The reason comes down to what the standard actually measures. ANSI does not measure your usable floor room by room. It measures each level's exterior footprint, the outline of the outside walls, and then makes a few subtractions for things that aren't finished living area. The gross living area of a home is the sum of those above-grade finished footprints.
A Cleveland appraiser explains it with a mental trick worth borrowing: picture the stairs as drop-stairs that could fold up flush into the upper floor. If they did, that opening would simply become more second-floor area. The stairs are second-floor area that happens to be tilted down into the stairwell. So the second floor gets credit for them. The first floor, measured as a solid rectangle to its outside walls, gets credit for the ground under them. Neither level is double-counting on purpose. Each is just measuring its own footprint, and the staircase happens to physically occupy space on both.
The worked example that clears it up
Standard staircases need no special math at all. If the opening in the upper floor is the same size as the stairs, you measure both floors to their exterior walls, the treads land on the upper level, the space beneath lands on the lower level, and you move on. The only time you do arithmetic is when the opening is bigger than the stairs, which is common when there's a railing, a hallway view, or an open two-story feel at the top of the flight.
Here is how that case works. Say your second floor measures 1,000 square feet to the exterior walls. Cut into that floor is a stairwell opening of 10 by 10, which is 100 square feet. The staircase itself is 3 feet wide by 8 feet long, so its footprint is 24 square feet. That leaves 76 square feet of the opening as an open void, floor that isn't there because you're looking down into the first floor.
You handle the second floor like this:
- Start with the full footprint: 1,000 square feet.
- Subtract the open void, the entire opening: minus 100 square feet.
- Add back the staircase footprint: plus 24 square feet.
- Second-floor finished area: 924 square feet.
The first floor is simpler. It's a solid 1,000-square-foot footprint measured to the outside walls, and nothing is subtracted, because the space under the stairs is still floor. So the first floor counts its full 1,000 square feet, including the 24 square feet the staircase rests on. Add the levels together and the home is 1,924 square feet. Notice what happened: the 24-square-foot stair footprint was added back on the second floor and was already baked into the first floor. It got counted on both. If you want to run these totals for your own home, the house calculator is built around this level-by-level method, and the step-by-step square footage guide walks through the measuring itself.
The rule of thumb: subtract the whole opening, then add the stairs back. You only ever subtract the part of the opening that is genuinely open to below.
Landings, split-levels, and half-flights
A landing is treated exactly like a tread. It's part of the flight, so it counts with the level the stairs descend from. A wide landing on a switchback staircase gets included in the upper level's area the same way the steps do.
Split-level homes look trickier than they are, because the same one-line rule handles them. Each short flight counts with the level it descends from. Stairs dropping from the entry level down to a lower living room count with the entry level. Stairs rising from that entry up to the bedroom level count with the bedroom level. You never have to decide whether a level is the "main" one. You just ask which floor each flight starts at, and assign it there. For the messier judgment calls about what does and doesn't make the cut, the guide on what counts as square footage covers the rest of the house.
One clearance note, since it comes up. ANSI does not enforce the usual 7-foot ceiling minimum on the space directly under a staircase. That storage closet or nook beneath the steps still counts as part of the lower level even with a low, sloped ceiling. Stairs are the exception to the height rule, not a victim of it.
Stairs down to an unfinished basement
This is the case people get backwards most often. If a staircase leads from your first floor down into an unfinished basement, the stairs still count, and they count in your above-grade finished square footage, right along with the first floor they descend from. They do not count as basement space.
The logic holds because the stairs descend from an above-grade, finished level, so that's where ANSI assigns them. The area underneath the basement stairs stays below-grade and does not join your gross living area, but the flight itself rides up with the level above it. So an unfinished basement can still add a little finished square footage to the house through its staircase alone. Below-grade space is always reported separately from the above-grade total, but the stairs connecting the two are an above-grade item.
Where the real-world confusion lives
Even licensed appraisers wrestle with this. In an AppraisersForum thread specifically about ANSI staircases, one appraiser had finished a McKissock ANSI course and still couldn't tell whether a finished staircase counts on both floors or just one, and whether you deduct anything when there's nothing usable under the stairs. A more experienced member walked it back to the standard itself: the stairs and landing count on the area they descend from, and because there's no minimum ceiling height for the space beneath the stairs, that space counts on the level below, which is exactly why the flight lands on both levels. Another veteran admitted he'd essentially ignored stairs for thirty years and measured them "wrong" the whole time, which tells you how counterintuitive this rule feels even to pros. If the people doing it for a living need a minute with it, you're in good company.
Frequently asked questions
Do stairs count as square footage twice?
Effectively, yes. The staircase is counted in the finished area of the floor it descends from, and the floor space beneath it is counted again on the level below. Since each level is measured to its own exterior footprint, the stair footprint ends up in both totals. That is correct under ANSI, not an error.
Which floor do stairs count on?
The level from which they descend. Stairs running from the second floor down to the first count with the second floor. Basement stairs descending from the first floor count with the first floor, in the above-grade area. You assign each flight to the level where it begins its descent.
Do you subtract the stairwell opening from the upper floor?
You subtract only the part of the opening that is open to below, then add the staircase footprint back. If the opening is exactly the size of the stairs, there's nothing open to subtract and no math to do. When the opening is larger, subtract the whole opening and add back the treads and landing.
Do stairs to an unfinished basement count as square footage?
Yes, but as above-grade finished area, counted with the floor above, not as basement space. The stairs descend from a finished, above-grade level, so ANSI assigns them there. The unfinished area under those stairs stays below-grade and out of your gross living area.
Does a landing count as square footage?
Yes. A landing is part of the flight and counts with the level the stairs descend from, the same as the treads. A wide switchback landing is included in the upper level's finished area.
Related tools and guides
Dig deeper with the ANSI Z765 standard explained, what counts as square footage, how to calculate square footage, the house square footage calculator, and what gross living area means.