Updated 2026-09-07

Building Code Glossary

Core: Building Code Definition

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

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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.

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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, 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 — 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 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	IBC 2009	43
Soils and Foundations	IBC 2009	36
Wall Construction	IRC 2009	25
Existing Structures	IBC 2009	23
Plastic	IBC 2009	23
Concrete	IBC 2009	12
Exterior Walls	IBC 2009	5
Definitions	IRC 2009	4
Special Detailed Requirements Based on Use and Occupancy	IBC 2009	3
Explosives and Fireworks	IFC 2009	3
Building Planning	IRC 2009	3
Definitions	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

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

The core and web dimensions shall comply with Table R611.

— IRC 2009 §R611.3.2

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 — 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 — 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 and the ICC 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.

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 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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