# Seismic Design Category: Building Code Definition

> How the IBC 2009 define seismic design category, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/seismic-design-category/
- 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 | IBC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IBC 2009 Structural Design (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 21 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Seismic design category is a defined term in the International Building Code (IBC) 2009, in Structural Design. The code's own words are: “A classification assigned to a structure based on its occupancy category and the severity of the design earthquake ground motion at the site.” No other I-Code in this corpus defines it, so the IBC 2009 definition is the one to work from. The term is used in 21 chapters of this corpus, most often in Soils and Foundations (IBC 2009), Building Planning (IRC 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?

**Seismic Design Category** — IBC 2009, Structural Design:

> A classification assigned to a structure based on its occupancy category and the severity of the design earthquake ground motion at the site.

![Labeled code-term definition diagram: Seismic Design Category: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/seismic-design-category/diagram-1344.webp)

*How the IBC 2009 define seismic design category, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Seismic Design Category** is defined once in this corpus, in the [Structural Design](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md) chapter of the International Building Code (IBC) 2009:

> A classification assigned to a structure based on its occupancy category and the severity of the design earthquake ground motion at the site.

## Where seismic design category is used in the code

The term appears in 21 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Soils and Foundations](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/soils-and-foundations.md) | IBC 2009 | 102 |
| [Building Planning](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md) | IRC 2009 | 78 |
| [Wall Construction](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md) | IRC 2009 | 67 |
| [Wood](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/wood.md) | IBC 2009 | 53 |
| [Structural Design](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md) | IBC 2009 | 47 |
| [Foundations](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/foundations.md) | IRC 2009 | 46 |
| [Structural Tests and Special Inspections](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-tests-and-special-inspections.md) | IBC 2009 | 43 |
| [Concrete](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md) | IBC 2009 | 25 |
| [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) | IBC 2009 | 13 |
| [Steel](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/steel.md) | IBC 2009 | 10 |
| [Wall Covering](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-covering.md) | IRC 2009 | 8 |
| [Exterior Walls](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/exterior-walls.md) | IBC 2009 | 4 |

_9 further chapters mention the term._

### The term in use

How the code actually writes about seismic design category, quoted from the 2009 text hosted here:

> Where a structure is assigned to Seismic Design Category D, E or F in accordance with Section 1613, individual spread footings founded on soil defined in Section 1613.5.2 as Site Class E or F shall be interconnected by ties.

— [IBC 2009 §1809.13](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/soils-and-foundations.md)

> Buildings shall be assigned a seismic design category in accordance with Figure R301.2(2).

— [IRC 2009 §R301.2.2.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md)

> The length of bracing along each braced wall line shall be the greater of that required by the design wind speed and braced wall line spacing in accordance with Table R602.10.1.2(1) as adjusted by the factors in the footnotes or the Seismic Design Category and braced wall line length in accordance with Table R602.10.1.2(2) as adjusted by the factors in …

— [IRC 2009 §R602.10.1.2](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md)


## The terms seismic design category is built out of

The definition above leans on 4 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what seismic design category covers:

- **[Design Earthquake Ground Motion](https://harth.build/resources/glossary/design-earthquake-ground-motion.md)** — IBC 2009: The earthquake ground motion that buildings and structures are specifically proportioned to resist in Section 1613.
- **[Occupancy Category](https://harth.build/resources/glossary/occupancy-category.md)** — IBC 2009: A category used to determine structural requirements based on occupancy.
- **[Occupancy](https://harth.build/resources/glossary/occupancy.md)** — IMC 2009: The purpose for which a building, or portion thereof, is utilized or occupied.
- **[Structure](https://harth.build/resources/glossary/structure.md)** — IPC 2009: That which is built or constructed or a portion thereof.

## Seismic Design Category: 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 IBC | Structural Design | |
| Re-check the requirement that uses it | Soils and Foundations (IBC 2009) | |
| Re-check the requirement that uses it | Building Planning (IRC 2009) | |
| Re-check the requirement that uses it | Wall Construction (IRC 2009) | |
| Re-check the requirement that uses it | Wood (IBC 2009) | |
| Confirm the dependent definition | Design Earthquake Ground Motion | |
| Confirm the dependent definition | Occupancy Category | |
| Confirm the dependent definition | Occupancy | |
| 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)
- [Design Earthquake Ground Motion: Building Code Definition](https://harth.build/resources/glossary/design-earthquake-ground-motion.md)
- [Occupancy Category: Building Code Definition](https://harth.build/resources/glossary/occupancy-category.md)
- [Structure: Building Code Definition](https://harth.build/resources/glossary/structure.md)
- [Occupancy: Building Code Definition](https://harth.build/resources/glossary/occupancy.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 seismic design category?

The International Building Code (IBC) 2009 defines it in Structural Design as: “A classification assigned to a structure based on its occupancy category and the severity of the design earthquake ground motion at the site.” 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 seismic design category?

In this corpus the term is used across 21 chapters, led by Soils and Foundations 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 my seismic design category?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Structural Design: “A classification assigned to a structure based on its occupancy category and the severity of the design earthquake ground motion at the site.” It is defined in IBC 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%2Fseismic-design-category%2F
- View this page in a browser: https://harth.build/resources/glossary/seismic-design-category/
- All resources for agents: https://harth.build/llms.txt