Do Staircases Count as GLA? How Stairs Are Measured in Appraisals

Staircases are one of the most commonly misunderstood areas in GLA measurement. The short answer: stair treads count as GLA on the floor they originate from, but the stairwell opening on the upper floor (the open-to-below area) is excluded. Here is exactly how appraisers handle this under ANSI Z765.

The ANSI Z765 rule for staircases

ANSI Z765-2021 measures GLA using the exterior perimeter of each floor. For multi-story homes, you calculate GLA separately for each floor level, then sum them.

The staircase itself sits on the first floor — the floor it originates from. The stair treads, risers, and the floor area beneath the staircase are all included in first-floor GLA because they fall within the exterior perimeter of that level.

On the upper floor, however, there is a stairwell opening — the hole in the floor that the staircase passes through. This area is open to below and does not have a usable floor surface. Under ANSI Z765, this open-to-below area must be subtracted from the upper floor GLA.

How it works in practice

First floor: Include the full exterior perimeter area. The staircase landing, treads, and any under-stair space are within this boundary and count as GLA.
Second floor: Start with the exterior perimeter area. Then subtract the stairwell opening (the open-to-below area). The remaining square footage is second-floor GLA.
Third floor and above: Same rule — exterior perimeter minus any open-to-below areas at that level.

The net effect is that a staircase is counted once — on the floor it starts from — and the opening it creates on the floor above is excluded. This is consistent and accurate: you are measuring usable floor area at each level.

Common scenarios

Scenario	How it is counted
Standard staircase (1st to 2nd floor)	Counted as GLA on 1st floor; stairwell opening subtracted from 2nd floor
Basement stairs (leading below grade)	Basement is below grade and does not count as GLA regardless — only the above-grade floors are measured
Open floating staircase	Same rule — counted on floor of origin; opening subtracted above
Spiral staircase	Same rule applies — measure the circular opening and subtract from upper floor
Split-level staircase	Count each landing level based on its grade relationship; consult ANSI Z765 split-level guidance
Under-stair storage	Counted as GLA on the floor it sits on (it is within the perimeter with ceiling height)

Ceiling height and under-stair space

The space under a staircase often has a sloped ceiling. ANSI Z765 requires at least 7 feet of ceiling height for GLA — but for sloped ceilings, at least half the area must meet the 7-foot threshold.

In practice: if the under-stair space has adequate headroom (it opens into a hallway or room), it counts as GLA. If the ceiling slopes so low that barely any of it is usable, it may not qualify. Most standard residential staircases have sufficient clearance on the first floor that the under-stair area counts without issue.

Measuring staircases in PlanSnapper

When tracing a multi-story floor plan in PlanSnapper:

First floor: Trace the full exterior perimeter, including the staircase area. No exclusion needed on this level.
Second floor: Trace the exterior perimeter, then use a second polygon to measure the stairwell opening. Subtract the stairwell area from the second-floor total to get accurate GLA.

PlanSnapper supports multiple polygons per project, so you can measure each floor separately and subtract open-to-below areas. The tool calculates area for each polygon — you combine the results in your report.

For most two-story homes, the stairwell opening is typically 30 to 50 square feet. Subtracting it makes the difference between an accurate ANSI measurement and an inflated one.

Need to measure GLA accurately?

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