# Panel Thickness: Building Code Definition > How the IRC 2009 define panel thickness, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/panel-thickness/ - 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 | 4 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Panel thickness is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “Thickness of core plus two layers of structural wood panel facings.” 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 4 chapters of this corpus, most often in Fire and Smoke Protection Features (IBC 2009), Definitions (IRC 2009), Concrete (IBC 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? **Panel Thickness** — IRC 2009, Definitions: > Thickness of core plus two layers of structural wood panel facings. ![Labeled code-term definition diagram: Panel Thickness: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/panel-thickness/diagram-1344.webp) *How the IRC 2009 define panel thickness, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Panel Thickness** 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: > Thickness of core plus two layers of structural wood panel facings. ## Where panel thickness is used in the code The term appears in 4 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 | 2 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 2 | | [Concrete](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md) | IBC 2009 | 1 | | [Wall Construction](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md) | IRC 2009 | 1 | ### The term in use How the code actually writes about panel thickness, quoted from the 2009 text hosted here: > The panel thickness and reinforcing shall reproduce the thickest and most congested area specified in the structural design. — [IBC 2009 §1913.5](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md) > SIPs shall comply with Figure R613.4 and shall have minimum panel thickness in accordance with Tables R613.5(1) and R613.5(2) for above-grade walls. — [IRC 2009 §R613.4](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md) ## Panel Thickness: 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 | Definitions (IRC 2009) | | | Re-check the requirement that uses it | Concrete (IBC 2009) | | | Re-check the requirement that uses it | Wall Construction (IRC 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 panel thickness? The International Residential Code (IRC) 2009 defines it in Definitions as: “Thickness of core plus two layers of structural wood panel facings.” 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 panel thickness? In this corpus the term is used across 4 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 minimum thickness of a shear wall according to IS code? Shear Wall is a separate defined term. The IBC 2009 defines it as: “A wall designed to resist lateral forces parallel to the plane of a wall.” That is not the same as panel thickness, which the IRC 2009 defines as “Thickness of core plus two layers of structural wood panel facings.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted. ### What is panel thickness? In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “Thickness of core plus two layers of structural wood panel facings.” 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. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fpanel-thickness%2F - View this page in a browser: https://harth.build/resources/glossary/panel-thickness/ - All resources for agents: https://harth.build/llms.txt