# Occupied Space: Building Code Definition

> How the IRC 2009 define occupied space, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/occupied-space/
- 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 | IRC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 20 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Occupied space is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The total area of all buildings or structures on any lot or parcel of ground prOjected on a horizontal plane, excluding permitted projections as allowed by this code.” No other I-Code in this corpus defines it, so the IRC 2009 definition is the one to work from. The term is used in 20 chapters of this corpus, most often in Fire and Smoke Protection Features (IBC 2009), Refrigeration (IMC 2009), Fire Protection Systems (IFC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted. Record the jurisdiction, the adopted edition, the application date and any local amendment that rewrites the definition before you use it on a live project, because a term redefined by amendment changes every requirement that depends on it.

*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?

**Occupied Space** — IRC 2009, Definitions:

> The total area of all buildings or structures on any lot or parcel of ground prOjected on a horizontal plane, excluding permitted projections as allowed by this code.

![Labeled code-term definition diagram: Occupied Space: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/occupied-space/diagram-1344.webp)

*How the IRC 2009 define occupied space, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Occupied Space** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) chapter of the International Residential Code (IRC) 2009:

> The total area of all buildings or structures on any lot or parcel of ground prOjected on a horizontal plane, excluding permitted projections as allowed by this code.

## Where occupied space is used in the code

The term appears in 20 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Fire and Smoke Protection Features](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md) | IBC 2009 | 13 |
| [Refrigeration](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/refrigeration.md) | IMC 2009 | 9 |
| [Fire Protection Systems](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/fire-protection-systems.md) | IFC 2009 | 8 |
| [Means of Egress](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/means-of-egress.md) | IBC 2009 | 7 |
| [Means of Egress](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/means-of-egress.md) | IFC 2009 | 7 |
| [Definitions](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/definitions.md) | IFC 2009 | 6 |
| [Ventilation](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/ventilation.md) | IMC 2009 | 6 |
| [Fire Protection Systems](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-protection-systems.md) | IBC 2009 | 4 |
| [Use and Occupancy Classification](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/use-and-occupancy-classification.md) | IBC 2009 | 4 |
| [Exhaust Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/exhaust-systems.md) | IMC 2009 | 4 |
| [Interior Environment](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/interior-environment.md) | IBC 2009 | 3 |
| [Building Services and Systems](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/building-services-and-systems.md) | IFC 2009 | 2 |

_8 further chapters mention the term._

### The term in use

How the code actually writes about occupied space, quoted from the 2009 text hosted here:

> Elevator hoistways shall be pressurized to maintain a minimum positive pressure of 0.10 inches of water (25 Pa) and a maximum positive pressure of 0.25 inches of water (67 Pa) with respect to adjacent occupied space on all floors.

— [IBC 2009 §708.14.2.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md)

> Where the refrigerant-containing parts of a system are located in one or more spaces that do not communicate through permanent openings or HVAC ducts, the volume of the smallest, enclosed occupied space shall be used to determine the permissible quantity of refrigerant in the system.

— [IMC 2009 §1104.4.1](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/refrigeration.md)

> Every occupied space shall be ventilated by natural means in accordance with Section 402 or by mechanical means in accordance with Section 403.

— [IMC 2009 §401.2](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/ventilation.md)

## Occupied Space: 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 IRC | Definitions | |
| Re-check the requirement that uses it | Fire and Smoke Protection Features (IBC 2009) | |
| Re-check the requirement that uses it | Refrigeration (IMC 2009) | |
| Re-check the requirement that uses it | Fire Protection Systems (IFC 2009) | |
| Re-check the requirement that uses it | Means of Egress (IBC 2009) | |
| 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)
- [Building: Building Code Definition](https://harth.build/resources/glossary/building.md)
- [Construction Documents: Building Code Definition](https://harth.build/resources/glossary/construction-documents.md)
- [Registered Design Professional: Building Code Definition](https://harth.build/resources/glossary/registered-design-professional.md)
- [Dwelling Unit: Building Code Definition](https://harth.build/resources/glossary/dwelling-unit.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 occupied space?

The International Residential Code (IRC) 2009 defines it in Definitions as: “The total area of all buildings or structures on any lot or parcel of ground prOjected on a horizontal plane, excluding permitted projections as allowed by this code.” 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 occupied space?

In this corpus the term is used across 20 chapters, led by Fire and Smoke Protection Features 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 is the definition of occupied space?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “The total area of all buildings or structures on any lot or parcel of ground prOjected on a horizontal plane, excluding permitted projections as allowed by this code.” It is defined in IRC 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.

### What does IRC mean in building code?

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 occupied space, which the IRC 2009 defines as “The total area of all buildings or structures on any lot or parcel of ground prOjected on a horizontal plane, excluding permitted projections as allowed by this code.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

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