Building Code Glossary
Net Occupiable Floor Area: Building Code Definition
How the IMC 2009 define net occupiable floor area, 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
Net occupiable floor area is a defined term in the International Mechanical Code (IMC) 2009, in Definitions. The code's own words are: “The floor area of an occupiable space defined by the inside surfaces of its walls but excluding shafts, column enclosures and other permanently enclosed, inaccessible and unoccupiable areas. Obstructions in the space such as furnishings, display or storage racks and other obstructions, whether temporary or permanent, shall not be deducted from the space area.” No other I-Code in this corpus defines it, so the IMC 2009 definition is the one to work from. The term is used in 2 chapters of this corpus, most often in Ventilation (IMC 2009), Definitions (IMC 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?
Net Occupiable Floor Area — IMC 2009, Definitions:
The floor area of an occupiable space defined by the inside surfaces of its walls but excluding shafts, column enclosures and other permanently enclosed, inaccessible and unoccupiable areas. Obstructions in the space such as furnishings, display or storage racks and other obstructions, whether temporary or permanent, shall not be deducted from the space area.
What must be verified before using this guidance?
Net Occupiable Floor Area is defined once in this corpus, in the Definitions chapter of the International Mechanical Code (IMC) 2009:
The floor area of an occupiable space defined by the inside surfaces of its walls but excluding shafts, column enclosures and other permanently enclosed, inaccessible and unoccupiable areas. Obstructions in the space such as furnishings, display or storage racks and other obstructions, whether temporary or permanent, shall not be deducted from the space area.
Where net occupiable floor area is used in the code
The term appears in 2 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Ventilation | IMC 2009 | 3 |
| Definitions | IMC 2009 | 1 |
The term in use
How the code actually writes about net occupiable floor area, quoted from the 2009 text hosted here:
Az Zone floor area: the net occupiable floor area of the space or spaces in the zone.
The terms net occupiable floor area is built out of
The definition above leans on 3 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what net occupiable floor area covers:
- Occupiable Space — IBC 2009: A room or enclosed space designed for human occupancy in which individuals congregate for
- Enclosed — IRC 2009: Surrounded by a case, housing, fence or walls that will prevent persons from accidentally contacting energized parts.
- Shall — IRC 2009: The term, when used in the code, is construed as mandatory.
Net Occupiable Floor Area: 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 IMC | Definitions | |
| Re-check the requirement that uses it | Ventilation (IMC 2009) | |
| Re-check the requirement that uses it | Definitions (IMC 2009) | |
| Confirm the dependent definition | Occupiable Space | |
| Confirm the dependent definition | Enclosed | |
| Confirm the dependent definition | Shall | |
| 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
- Occupiable Space: Building Code Definition
- Enclosed: 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 net occupiable floor area?
The International Mechanical Code (IMC) 2009 defines it in Definitions as: “The floor area of an occupiable space defined by the inside surfaces of its walls but excluding shafts, column enclosures and other permanently enclosed, inaccessible and unoccupiable areas. Obstructions in the space such as furnishings, display or storage racks and other obstructions, whether temporary or permanent, shall not be deducted from the space area.” 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 net occupiable floor area?
In this corpus the term is used across 2 chapters, led by Ventilation in the IMC 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 is the difference between floor area and building area?
Building is a separate defined term. The IBC 2009 defines it as: “Any structure used or intended for supporting or sheltering any use or occupancy.” That is not the same as net occupiable floor area, which the IMC 2009 defines as “The floor area of an occupiable space defined by the inside surfaces of its walls but excluding shafts, column enclosures and other permanently enclosed, inaccessible and unoccupiable areas. Obstructions in the space such as furnishings, display or storage racks and …” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
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