# 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.

- Canonical: https://harth.build/resources/glossary/net-occupiable-floor-area/
- Last updated: 2026-09-07
- Data source: 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.

## Key facts

| Fact | Value |
| --- | --- |
| Defined in | IMC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IMC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 2 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## 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](https://nz.linkedin.com/in/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.

![Labeled code-term definition diagram: Net Occupiable Floor Area: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/net-occupiable-floor-area/diagram-1344.webp)

*How the IMC 2009 define net occupiable floor area, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Net Occupiable Floor Area** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) 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](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/ventilation.md) | IMC 2009 | 3 |
| [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) | 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.

— [IMC 2009, Ventilation](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/ventilation.md)


## 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](https://harth.build/resources/glossary/occupiable-space.md)** — IBC 2009: A room or enclosed space designed for human occupancy in which individuals congregate for
- **[Enclosed](https://harth.build/resources/glossary/enclosed.md)** — IRC 2009: Surrounded by a case, housing, fence or walls that will prevent persons from accidentally contacting energized parts.
- **[Shall](https://harth.build/resources/glossary/shall.md)** — 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](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-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](https://harth.build/resources/glossary.md)
- [Occupiable Space: Building Code Definition](https://harth.build/resources/glossary/occupiable-space.md)
- [Enclosed: Building Code Definition](https://harth.build/resources/glossary/enclosed.md)

## 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](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.

### Source links

- [codes.iccsafe.org](https://codes.iccsafe.org/codes)

- [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/)

## 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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