Building Code Glossary
Atrium: Building Code Definition
How the IBC 2009, IFC 2009 define atrium, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.
Direct answer
Atrium is a defined term in the International Building Code (IBC) 2009, in Special Detailed Requirements Based on Use and Occupancy. The code's own words are: “An opening connecting two or more stories other than enclosed stairways, elevators, hoistways, escalators, plumbing, electrical, air-conditioning or other equipment, which is closed at the top and not defined as a mall. Stories, as used in this definition, do not include balconies within assembly groups or mezzanines that comply with Section 505.” The IFC 2009 defines the same term with different wording, so the controlling text depends on which code governs the question in front of you — the comparison below sets the versions side by side. The term is used in 14 chapters of this corpus, most often in Special Detailed Requirements Based on Use and Occupancy (IBC 2009), Fire Protection Systems (IFC 2009), Fire and Smoke Protection Features (IBC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.
Content and cited inputs reviewed by Scott Barrington, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Atrium — IBC 2009, Special Detailed Requirements Based on Use and Occupancy:
An opening connecting two or more stories other than enclosed stairways, elevators, hoistways, escalators, plumbing, electrical, air-conditioning or other equipment, which is closed at the top and not defined as a mall. Stories, as used in this definition, do not include balconies within assembly groups or mezzanines that comply with Section 505.
What must be verified before using this guidance?
Two of the I-Codes in this corpus define Atrium, and the wording is not identical — read the version that governs your question.
| Code | Where it is defined | Definition |
|---|---|---|
| IBC 2009 | Special Detailed Requirements Based on Use and Occupancy | An opening connecting two or more stories other than enclosed stairways, elevators, hoistways, escalators, plumbing, electrical, air-conditioning or other equipment, which is closed at the top and not defined as a mall. Stories, as used in this definition, do not include balconies within assembly groups or mezzanines that comply with Section 505. |
| IFC 2009 | Definitions | An opening connecting two or more stories other than enclosed stairways, elevators, hoistways, escalators, plumbing, electrical, air-conditioning or other equipment, which is closed at the top and not defined as a mall. Stories, as used in this definition, do not include balconies within assembly groups or mezzanines that comply with Section 505 of the International Building Code. |
Where atrium is used in the code
The term appears in 14 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Special Detailed Requirements Based on Use and Occupancy | IBC 2009 | 38 |
| Fire Protection Systems | IFC 2009 | 21 |
| Fire and Smoke Protection Features | IBC 2009 | 14 |
| Fire Protection Systems | IBC 2009 | 7 |
| Means of Egress | IBC 2009 | 6 |
| Means of Egress | IFC 2009 | 6 |
| Construction Requirements for Existing Buildings | IFC 2009 | 4 |
| Special Construction | IBC 2009 | 2 |
| Definitions | IBC 2009 | 1 |
| Plastic | IBC 2009 | 1 |
| Definitions | IFC 2009 | 1 |
| Emergency Planning and Preparedness | IFC 2009 | 1 |
2 further chapters mention the term.
The term in use
How the code actually writes about atrium, quoted from the 2009 text hosted here:
Where a covered mall building contains an atrium, a smoke control system shall be provided in accordance with Section 404.5.
A fire alarm system shall be installed in occupancies with an atrium that connects more than two stories, with smoke detection installed throughout the atrium.
In other than Group I occupancies, interior vertical openings in a covered mall building or a building with an atrium shall be protected by either I-hour fire-resistance-rated construction or an automatic sprinkler system shall be installed throughout the building in accordance with Section 903.3.1.1 or 903.3.1.2.
The terms atrium is built out of
The definition above leans on 4 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what atrium covers:
- Equipment — IRC 2009: All piping, ducts, vents, control devices and other components of systems other than appliances that are permanently installed and integrated to provide control of environmental conditions for buildings.
- Building — IBC 2009: Any structure used or intended for supporting or sheltering any use or occupancy.
- Plumbing — IRC 2009: For the purpose of this code, plumbing refers to those installations, repairs, maintenance and alterations regulated by Chapters 25 through 33.
- Enclosed — IRC 2009: Surrounded by a case, housing, fence or walls that will prevent persons from accidentally contacting energized parts.
Atrium: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IBC | Special Detailed Requirements Based on Use and Occupancy | |
| Read the definition in the adopted IFC | Definitions | |
| Re-check the requirement that uses it | Special Detailed Requirements Based on Use and Occupancy (IBC 2009) | |
| Re-check the requirement that uses it | Fire Protection Systems (IFC 2009) | |
| Re-check the requirement that uses it | Fire and Smoke Protection Features (IBC 2009) | |
| Re-check the requirement that uses it | Fire Protection Systems (IBC 2009) | |
| Confirm the dependent definition | Equipment | |
| Confirm the dependent definition | Building | |
| Confirm the dependent definition | Plumbing | |
| Local amendment to any of the above | Jurisdiction's amendment list |
A research aid, not a code determination. The authority having jurisdiction decides which edition and which amendments apply.
Where can you explore related guidance?
- Explore all glossary guidance
- Equipment: Building Code Definition
- Plumbing: Building Code Definition
- Enclosed: Building Code Definition
- Building: Building Code Definition
Sources and method
Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The ICC code library publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of atrium?
The International Building Code (IBC) 2009 defines it in Special Detailed Requirements Based on Use and Occupancy as: “An opening connecting two or more stories other than enclosed stairways, elevators, hoistways, escalators, plumbing, electrical, air-conditioning or other equipment, which is closed at the top and not defined as a mall. Stories, as used in this definition, do not include balconies within assembly groups or mezzanines that comply with Section 505.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.
Which parts of the code depend on atrium?
In this corpus the term is used across 14 chapters, led by Special Detailed Requirements Based on Use and Occupancy in the IBC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.
What does atrium mean in a building?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Special Detailed Requirements Based on Use and Occupancy: “An opening connecting two or more stories other than enclosed stairways, elevators, hoistways, escalators, plumbing, electrical, air-conditioning or other equipment, which is closed at the top and not defined as a mall. Stories, as used in this definition, do not include balconies within assembly groups or mezzanines that comply with Section 505.” It is defined in IBC 2009, IFC 2009. It is not the same as Building, which the IBC 2009 defines separately as “Any structure used or intended for supporting or sheltering any use or occupancy.” Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
What is an atrium vs courtyard?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Special Detailed Requirements Based on Use and Occupancy: “An opening connecting two or more stories other than enclosed stairways, elevators, hoistways, escalators, plumbing, electrical, air-conditioning or other equipment, which is closed at the top and not defined as a mall. Stories, as used in this definition, do not include balconies within assembly groups or mezzanines that comply with Section 505.” It is defined in IBC 2009, IFC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
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