How an "Interior" Exit Stair Can Be Almost Entirely Open to the Outdoors

The California Building Code's term "interior exit stairway" describes a regulatory category, not a physical enclosure. Buildings throughout San Diego use exit stairs that are open along their walls, open at the top, or both — and the code permits it.

Apr 28, 20268 min readbuilding code, egress, multifamily design

If you've spent time in San Diego's mid-rise apartment buildings, you've probably walked through an exit stair that's mostly outdoors. Maybe it had no roof — just open sky overhead. Maybe one of its walls was replaced with a guardrail you could see through, with breeze and daylight coming straight in. Maybe both. These stairs are common in San Diego, and they look nothing like what most people imagine when they hear "interior exit stair."

The reason is a quirk in how the building code works. The code uses the term "interior exit stairway" to describe a kind of fire-protected egress system, not a stair that's physically inside a building. As long as the stair meets the fire-protection requirements — including how it separates from the spaces around it — it can be substantially open to weather, daylight, and outdoor air. It can be missing a roof. It can be missing one or more of its walls. It can be functionally outdoors in every visual sense, while still qualifying as "interior" under the code.

This isn't a loophole. It's the way the code is designed. And it has been formally confirmed by the International Code Council's senior technical staff. Yet it surprises out-of-region architects, frustrates Authorities Having Jurisdiction who misinterpret the rules, and represents one of the most underused design opportunities in San Diego multifamily construction.

What the code actually requires

The relevant section of the California Building Code (Section 1023, governing interior exit stairways) sets out specific requirements for these stairs. In plain language, the requirements that matter most:

The stair must be separated from the rest of the building by walls that resist fire for a specified time — one hour for stairs serving fewer than four stories, two hours for stairs serving four or more. The doors connecting the stair to occupied floors must also be fire-rated.
The stair must lead to a place where occupants can exit the building — typically directly to the street or to an approved exit pathway that does.
Doors and other openings into the stair are restricted. Doors must be fire-rated. Most other openings between the stair and the rest of the building are prohibited.

That's the core of it. Notice what's not on this list: the code does not say the stair has to have a roof. It does not say the stair has to be conditioned, ventilated, weather-tight, or fully enclosed by walls on all sides. It says the stair has to be separated from the rest of the building by fire-rated construction, and it has to function as a safe egress route.

The "interior" in "interior exit stairway" is regulatory shorthand for "fire-protected egress that's part of the building's exit system." It doesn't describe physical containment.

What this means in practice

Because the code's requirements are about fire separation rather than physical enclosure, the stair can take forms that look outdoor-like:

Open at the top. The stair has no roof. Rain falls into the stairwell. Daylight enters from above. The stair walls have proper fire ratings, but nothing covers the stair from above.
Open along a wall. One or more of the stair's vertical walls is replaced with a guardrail (typically 42 inches tall) or an open screen. Wind, daylight, and outdoor air pass freely through the stair from one or more sides. From outside the building, the stair looks like an outdoor balcony or open exterior corridor — but it's serving the same egress function as a fully enclosed interior stair.
Open on multiple sides. A stair located at a corner of the building can have two of its walls open, with only the wall separating it from the building's interior fully constructed. The result is a stair that's almost entirely outdoor in its character but still qualifies as an "interior" exit stair under the code.

In each case, the determining factor is that the wall separating the stair from the rest of the building's interior remains a fire-rated barrier. That's what makes the stair "interior" in the regulatory sense. The rest of the stair's enclosure — the parts facing outward — can be substantially open as long as overall fire separation requirements between the building and adjacent properties are met.

When this interpretation has been formally tested

This isn't a fringe interpretation. It has been put to the International Code Council's senior technical staff in writing, and the ICC has confirmed that the code permits substantially open stairs to qualify as "interior."

The question came up in a 2025 ICC Quick Consult opinion concerning a three-story apartment building in San Diego. The architect designed the project's exit stairs to be largely open along their outer walls, with the open portions replaced by guardrails. The local Authority Having Jurisdiction rejected the design, citing the language in the building code stating that interior exit stairways "shall be enclosed." The AHJ's position was that "enclosed" had to mean physically walled in on all sides.

The ICC's senior technical staff, in a written opinion, disagreed. The relevant conclusion: the code does not require interior exit stairways to be completely enclosed. Where the stair's exterior walls are not specifically required to be fire-resistance rated for their distance from the property line, those walls "could be eliminated altogether and replaced with a 42-inch high guard or some sort of open screen system." Even though such a stair might "appear to be an exterior exit stairway due to the openness," it can still qualify as an interior exit stair under the code as long as it meets all the actual requirements of Section 1023.

This is the authoritative interpretation. The ICC's position, in plain language: an interior exit stair can have walls that are nearly entirely open, or no roof, or both — provided the stair meets the fire-separation requirements that distinguish "interior exit stair" from other kinds of stairs.

Why this matters

The design and economic consequences of using a substantially open exit stair are real:

Mechanical systems are simpler. A fully enclosed stair often requires its own ventilation system — separate ductwork, fans, and the construction needed to enclose those systems. A stair that's open to outdoor air doesn't need a mechanical ventilation system at all. Outdoor air provides ventilation passively. An entire mechanical subsystem disappears from the project.
Construction is less expensive. Walls and roofs that don't exist don't cost anything to build. A stair with two walls and no roof is materially less expensive to construct than a stair with four walls and a roof, even setting aside mechanical systems.
Floor plate is recovered. A roof over the stair occupies space at the top of the building. Eliminating the roof means the floor that would have been the stair's roof can become rentable area on the upper floor — a real recurring revenue gain over the building's life.
Daylight and air quality improve. A stair open to outdoor air is naturally lit and ventilated. It doesn't require artificial lighting during the day, doesn't smell like a sealed concrete shaft, and is genuinely pleasant to use — which matters more for resident experience than the code accounts for.
Maintenance is reduced over the building's life. Fewer walls and no roof means fewer surfaces to maintain, repaint, and repair. The materials chosen for outdoor exposure (typically galvanized steel guards, weather-resistant concrete, etc.) are durable and require less ongoing intervention than enclosed-stair finishes.

Why this works in San Diego specifically

San Diego's climate is unusually well-suited to this approach. Annual rainfall is low and concentrated in a few months. Temperature extremes are mild. Cold weather is rare. Humidity is moderate. The conditions that would make an open stair uncomfortable or impractical in colder, wetter, or stormier climates rarely apply here.

The result: substantially open exit stairs are a routine feature of San Diego multifamily and commercial construction, particularly in mid-rise infill projects. Architects designing in San Diego learn this approach early. Architects new to San Diego — or developers familiar with markets where the climate makes openness unworkable — often don't realize the option exists.

When an AHJ disagrees

The ICC's interpretation is advisory rather than binding. The final decision on any specific project rests with the local Authority Having Jurisdiction.

In practice, most San Diego AHJs are familiar with substantially open exit stairs and approve them routinely as long as the design demonstrates compliance with the actual requirements of the code. Occasionally, an AHJ misinterprets the "enclosed" language and rejects a design that would otherwise be code-compliant. When this happens, the architect's response should be to document the design's compliance with the relevant fire-separation requirements and reference the ICC opinion as supporting interpretation. AHJs are not obligated to follow ICC opinions, but the documentation supports a strong technical case.

For a developer or owner watching this play out, the right framing is that the design itself is sound. An AHJ disagreement about interpretation is resolvable through documentation rather than through redesign.

What this means for project feasibility

For any San Diego multifamily or mixed-use project, the choice between a fully enclosed stair and a substantially open stair is a meaningful design decision with material consequences for cost, mechanical systems, floor plate efficiency, and ongoing operations. Projects that default to fully enclosed stairs because that's what the term "interior" suggests are typically choosing the more expensive option without realizing they had a choice.

The code tells you what an exit stair has to be. It doesn't tell you what one has to look like — and the difference between those two questions is where San Diego architects have been quietly building better, more economical buildings for years.

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