# Design Strength: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/design-strength/
- 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 | 7 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Design strength is a defined term in the International Building Code (IBC) 2009, in Structural Design. The code's own words are: “The product of the nominal strength and a resistance factor (or strength reduction factor).” 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 7 chapters of this corpus, most often in Wall Construction (IRC 2009), Concrete (IBC 2009), Structural Design (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?

**Design Strength** — IBC 2009, Structural Design:

> The product of the nominal strength and a resistance factor (or strength reduction factor).

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

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

## What must be verified before using this guidance?

**Design Strength** 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:

> The product of the nominal strength and a resistance factor (or strength reduction factor).

## Where design strength is used in the code

The term appears in 7 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Wall Construction](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md) | IRC 2009 | 20 |
| [Concrete](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md) | IBC 2009 | 15 |
| [Structural Design](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md) | IBC 2009 | 5 |
| [Structural Tests and Special Inspections](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-tests-and-special-inspections.md) | IBC 2009 | 4 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 3 |
| [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) | IBC 2009 | 2 |
| [Steel](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/steel.md) | IBC 2009 | 1 |

### The term in use

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

> Where reduction factors for design strength, R3, from Table R611.7 (4) based on horizontal and vertical shear reinforcement being provided are used, solid wall segments shall have horizontal reinforcement consisting of minimum No.4 bars.

— [IRC 2009 §R611.7.2.2.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md)

> - Connections that are designed to yield shall be capable of maintaining 80 percent of their design strength at the deformation induced by the design displacement or shall use Type 2 mechanical splices.

— [IBC 2009 §21.4.3](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md)

> Each column splice shall have the minimum design strength in tension to transfer the design dead and live load tributary to the column between the splice and the splice or base immediately below.

— [IBC 2009 §1614.3.2.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md)


## Design Strength compared with Factored Load

These two are the closest pair in the 2009 I-Codes: about 46 per cent of their defining words are the same. The code states both and compares neither, so the difference is worth naming.

| | Wording unique to it |
| --- | --- |
| **Design Strength** (IBC 2009) | strength, resistance, reduction |
| [Factored Load](https://harth.build/resources/glossary/factored-load.md) (IBC 2009) | ofa, load |

Everything else in the two definitions is shared. If a project turns on which of the two applies, those words are the whole of the test — and a local amendment that edits one of them without editing the other moves the boundary between design strength and factored load.

## The terms design strength is built out of

The definition above leans on 1 other defined term. Each carries its own code definition, and a local amendment to any of them changes what design strength covers:

- **[Resistance Factor](https://harth.build/resources/glossary/resistance-factor.md)** — IBC 2009: A factor that accounts for deviations of the actual strength from the nominal strength and the manner and consequences of failure (also called "strength reduction factor").

## Design Strength: 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 | Wall Construction (IRC 2009) | |
| Re-check the requirement that uses it | Concrete (IBC 2009) | |
| Re-check the requirement that uses it | Structural Design (IBC 2009) | |
| Re-check the requirement that uses it | Structural Tests and Special Inspections (IBC 2009) | |
| Confirm the dependent definition | Resistance Factor | |
| 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)
- [Resistance Factor: Building Code Definition](https://harth.build/resources/glossary/resistance-factor.md)
- [Design Flood Elevation: Building Code Definition](https://harth.build/resources/glossary/design-flood-elevation.md)
- [Loads: Building Code Definition](https://harth.build/resources/glossary/loads.md)
- [Seismic Design Category: Building Code Definition](https://harth.build/resources/glossary/seismic-design-category.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 design strength?

The International Building Code (IBC) 2009 defines it in Structural Design as: “The product of the nominal strength and a resistance factor (or strength reduction factor).” 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 design strength?

In this corpus the term is used across 7 chapters, led by Wall Construction in the IRC 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 concrete design strength?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Structural Design: “The product of the nominal strength and a resistance factor (or strength reduction factor).” 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.

### What does IBC mean in building codes?

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 design strength, which the IBC 2009 defines as “The product of the nominal strength and a resistance factor (or strength reduction factor).” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

### What is the design strength of steel?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Structural Design: “The product of the nominal strength and a resistance factor (or strength reduction factor).” It is defined in IBC 2009. It is not the same as Steel, which the IFC 2009 defines separately as “Hot-or cold-rolled as defined by the International Building Code.” 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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