# Core: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/core/
- 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 | 22 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Core is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The light-weight middle section of the structural insulated panel composed of foam plastic insulation, which provides the link between the two facing shells.” 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 22 chapters of this corpus, most often in Fire and Smoke Protection Features (IBC 2009), Soils and Foundations (IBC 2009), Wall Construction (IRC 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?

**Core** — IRC 2009, Definitions:

> The light-weight middle section of the structural insulated panel composed of foam plastic insulation, which provides the link between the two facing shells.

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

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

## What must be verified before using this guidance?

**Core** 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 light-weight middle section of the structural insulated panel composed of foam plastic insulation, which provides the link between the two facing shells.

## Where core is used in the code

The term appears in 22 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 | 43 |
| [Soils and Foundations](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/soils-and-foundations.md) | IBC 2009 | 36 |
| [Wall Construction](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md) | IRC 2009 | 25 |
| [Existing Structures](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/existing-structures.md) | IBC 2009 | 23 |
| [Plastic](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/plastic.md) | IBC 2009 | 23 |
| [Concrete](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md) | IBC 2009 | 12 |
| [Exterior Walls](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/exterior-walls.md) | IBC 2009 | 5 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 4 |
| [Special Detailed Requirements Based on Use and Occupancy](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/special-detailed-requirements-based-on-use-and-occupancy.md) | IBC 2009 | 3 |
| [Explosives and Fireworks](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/explosives-and-fireworks.md) | IFC 2009 | 3 |
| [Building Planning](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md) | IRC 2009 | 3 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 2 |

_10 further chapters mention the term._

### The term in use

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

> For hollow-core precast concrete wall panels in which the cores are of constant cross section throughout the length, calculation of the equivalent thickness by dividing the net cross-sectional area (the gross cross section minus the area of the cores) of the panel by its width shall be permitted.

— [IBC 2009 §721.2.1.1.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md)

> For structures assigned to Seismic Design Category C, D, E or F in accordance with Section 1613, the ends of hoops, spirals and ties used in concrete deep foundation elements shall be terminated with seismic hooks, as defined in ACI 318, and shall be turned into the confined concrete core.

— [IBC 2009 §1810.3.2.1.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/soils-and-foundations.md)

> The core and web dimensions shall comply with Table R611.

— [IRC 2009 §R611.3.2](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md)


## The terms core is built out of

The definition above leans on 2 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what core covers:

- **[Foam Plastic Insulation](https://harth.build/resources/glossary/foam-plastic-insulation.md)** — IBC 2009: A plastic that is intentionally expanded by the use of a foaming agent to produce a reduced-density plastic containing voids consisting of open or closed cells distributed throughout the plastic for thermal insu-1ating or acoustical purposes and that has a …
- **[Facing](https://harth.build/resources/glossary/facing.md)** — IRC 2009: The wood structural panel facings that form the two outmost rigid layers of the structural insulated panel.

## Core: 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 | Soils and Foundations (IBC 2009) | |
| Re-check the requirement that uses it | Wall Construction (IRC 2009) | |
| Re-check the requirement that uses it | Existing Structures (IBC 2009) | |
| Confirm the dependent definition | Foam Plastic Insulation | |
| Confirm the dependent definition | Facing | |
| 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)
- [Foam Plastic Insulation: Building Code Definition](https://harth.build/resources/glossary/foam-plastic-insulation.md)
- [Facing: Building Code Definition](https://harth.build/resources/glossary/facing.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 core?

The International Residential Code (IRC) 2009 defines it in Definitions as: “The light-weight middle section of the structural insulated panel composed of foam plastic insulation, which provides the link between the two facing shells.” 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 core?

In this corpus the term is used across 22 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 a building core?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “The light-weight middle section of the structural insulated panel composed of foam plastic insulation, which provides the link between the two facing shells.” It is defined in IRC 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 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 core, which the IRC 2009 defines as “The light-weight middle section of the structural insulated panel composed of foam plastic insulation, which provides the link between the two facing shells.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

### What does shell and core mean?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “The light-weight middle section of the structural insulated panel composed of foam plastic insulation, which provides the link between the two facing shells.” It is defined in IRC 2009. It is not the same as Shell, which the IBC 2009 defines separately as “The outer portion of a hollow masonry unit as placed in masonry.” 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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