# Ridge: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/ridge/
- 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 | 21 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Ridge is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “With respect to topographic wind effects, an elongated crest of a hill characterized by strong relief in two directions.” 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 21 chapters of this corpus, most often in Roof-ceiling Construction (IRC 2009), Structural Design (IBC 2009), Building Planning (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?

**Ridge** — IRC 2009, Definitions:

> With respect to topographic wind effects, an elongated crest of a hill characterized by strong relief in two directions.

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

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

## What must be verified before using this guidance?

**Ridge** 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:

> With respect to topographic wind effects, an elongated crest of a hill characterized by strong relief in two directions.

## Where ridge 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 |
| --- | --- | --- |
| [Roof-ceiling Construction](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/roof-ceiling-construction.md) | IRC 2009 | 38 |
| [Structural Design](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md) | IBC 2009 | 30 |
| [Building Planning](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md) | IRC 2009 | 23 |
| [Wood](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/wood.md) | IBC 2009 | 12 |
| [Explosives and Fireworks](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/explosives-and-fireworks.md) | IFC 2009 | 10 |
| [Fire Service Features](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/fire-service-features.md) | IFC 2009 | 10 |
| [Fire Protection Systems](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/fire-protection-systems.md) | IFC 2009 | 8 |
| [Flammable and Combustible Liquids](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/flammable-and-combustible-liquids.md) | IFC 2009 | 6 |
| [Roof Assemblies](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/roof-assemblies.md) | IRC 2009 | 6 |
| [Roof Assemblies and Rooftop Structures](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/roof-assemblies-and-rooftop-structures.md) | IBC 2009 | 3 |
| [Exhaust Systems](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/exhaust-systems.md) | IRC 2009 | 3 |
| [Glass and Glazing](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/glass-and-glazing.md) | IBC 2009 | 2 |

_9 further chapters mention the term._

### The term in use

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

> Rafters shall be framed to ridge board or to each other with a gusset plate as a tie.

— [IRC 2009 §R802.3](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/roof-ceiling-construction.md)

> Any glazing material is permitted to be installed without screening in the sloped areas of greenhouses, provided the greenhouse height at the ridge does not exceed 20 feet (6096 mm) above grade.

— [IRC 2009 §R308.6.6](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md)

> Where the roof slope is less than three units vertical in 12 units horizontal (25-percent slope), members supporting rafters and ceilingjoists such as ridge board, hips and valleys shall be designed as beams.

— [IBC 2009 §2308.10](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/wood.md)


## Ridge compared with Hill

These two are the closest pair in the 2009 I-Codes: about 50 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 |
| --- | --- |
| **Ridge** (IRC 2009) | elongated, crest, hill, two, directions |
| [Hill](https://harth.build/resources/glossary/hill.md) (IRC 2009) | land, surface, horizontal, direction |

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 ridge and hill.

## Ridge: 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 | Roof-ceiling Construction (IRC 2009) | |
| Re-check the requirement that uses it | Structural Design (IBC 2009) | |
| Re-check the requirement that uses it | Building Planning (IRC 2009) | |
| Re-check the requirement that uses it | Wood (IBC 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 ridge?

The International Residential Code (IRC) 2009 defines it in Definitions as: “With respect to topographic wind effects, an elongated crest of a hill characterized by strong relief in two directions.” 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 ridge?

In this corpus the term is used across 21 chapters, led by Roof-ceiling 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 the definition of a ridge in a building?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “With respect to topographic wind effects, an elongated crest of a hill characterized by strong relief in two directions.” 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 ridge in construction?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “With respect to topographic wind effects, an elongated crest of a hill characterized by strong relief in two directions.” 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.

### What is considered a structure in building code?

Structure is a separate defined term. The IPC 2009 defines it as: “That which is built or constructed or a portion thereof.” That is not the same as ridge, which the IRC 2009 defines as “With respect to topographic wind effects, an elongated crest of a hill characterized by strong relief in two directions.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

---

- Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fridge%2F
- View this page in a browser: https://harth.build/resources/glossary/ridge/
- All resources for agents: https://harth.build/llms.txt