# Main: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/main/
- 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, IPC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 135 (counted across the codes hosted here) |
| Wording identical across codes | No (compare before citing one code's wording under another) |

## Direct answer

Main is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The principal pipe artery to which branches may be connected.” The IPC 2009 words it differently, in Definitions: “The principal pipe artery to which branches are connected.” The IPC 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 135 chapters of this corpus, most often in Flammable and Combustible Liquids (IFC 2009), Fire Protection Systems (IFC 2009), Means of Egress (IFC 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?

**Main** — IRC 2009, Definitions:

> The principal pipe artery to which branches may be connected.

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

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

## What must be verified before using this guidance?

Two of the I-Codes in this corpus define **Main**, and the wording is not identical — read the version that governs your question.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IRC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | The principal pipe artery to which branches may be connected. |
| IPC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/definitions.md) | The principal pipe artery to which branches are connected. |

## Where main is used in the code

The term appears in 135 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Flammable and Combustible Liquids](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/flammable-and-combustible-liquids.md) | IFC 2009 | 182 |
| [Fire Protection Systems](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/fire-protection-systems.md) | IFC 2009 | 174 |
| [Means of Egress](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/means-of-egress.md) | IFC 2009 | 107 |
| [Means of Egress](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/means-of-egress.md) | IBC 2009 | 90 |
| [Fire Protection Systems](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-protection-systems.md) | IBC 2009 | 87 |
| [Aviation Facilities](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/aviation-facilities.md) | IFC 2009 | 77 |
| [Fire and Smoke Protection Features](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md) | IBC 2009 | 71 |
| [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | IRC 2009 | 71 |
| [Motor Fuel-dispensing Facilities and Repair Garages](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/motor-fuel-dispensing-facilities-and-repair-garages.md) | IFC 2009 | 66 |
| [Scope and Administration](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/scope-and-administration.md) | IFC 2009 | 64 |
| [Building Services and Systems](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/building-services-and-systems.md) | IFC 2009 | 63 |
| [Fire Service Features](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/fire-service-features.md) | IFC 2009 | 55 |

_123 further chapters mention the term._

### The term in use

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

> Main aisles shall be a minimum of 8 feet (2438 mm) wide.

— [IFC 2009 §3404.3.3.6](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/flammable-and-combustible-liquids.md)

> Wiring for operation and control of smoke exhaust fans shall be connected ahead of the main disconnect and protected against exposure to temperatures in excess of 1,000°F (538°C) for a period of not less than 15 minutes.

— [IFC 2009 §910.4.4](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/fire-protection-systems.md)

> Every room or space that is an assembly occupancy shall have the occupant load of the room or space posted in a conspicuous place, near the main exit or exit access doorway from the room or space.

— [IFC 2009 §1004.3](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/means-of-egress.md)

## Main: 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 | |
| Read the definition in the adopted IPC | Definitions | |
| Re-check the requirement that uses it | Flammable and Combustible Liquids (IFC 2009) | |
| Re-check the requirement that uses it | Fire Protection Systems (IFC 2009) | |
| Re-check the requirement that uses it | Means of Egress (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 main?

The International Residential Code (IRC) 2009 defines it in Definitions as: “The principal pipe artery to which branches may be connected.” 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 main?

In this corpus the term is used across 135 chapters, led by Flammable and Combustible Liquids in the IFC 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 a 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 main, which the IRC 2009 defines as “The principal pipe artery to which branches may be connected.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

### What is the main purpose of building codes?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “The principal pipe artery to which branches may be connected.” It is defined in IRC 2009, IPC 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.

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