# Hill: Building Code Definition > How the IRC 2009 define hill, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/hill/ - 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 | 12 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Hill 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, a land surface characterized by strong relief in any horizontal direction.” 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 12 chapters of this corpus, most often in Commercial Energy Efficiency (IECC 2009), Building Planning (IRC 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? **Hill** — IRC 2009, Definitions: > With respect to topographic wind effects, a land surface characterized by strong relief in any horizontal direction. ![Labeled code-term definition diagram: Hill: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/hill/diagram-1344.webp) *How the IRC 2009 define hill, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Hill** 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, a land surface characterized by strong relief in any horizontal direction. ## Where hill is used in the code The term appears in 12 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next. | Chapter | Code | Mentions | | --- | --- | --- | | [Commercial Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/commercial-energy-efficiency.md) | IECC 2009 | 44 | | [Building Planning](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md) | IRC 2009 | 21 | | [Structural Design](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md) | IBC 2009 | 15 | | [Hydronic Piping](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/hydronic-piping.md) | IMC 2009 | 4 | | [Existing Structures](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/existing-structures.md) | IBC 2009 | 3 | | [Explosives and Fireworks](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/explosives-and-fireworks.md) | IFC 2009 | 3 | | [Scope and Administration](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/scope-and-administration.md) | IBC 2009 | 2 | | [Use and Occupancy Classification](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/use-and-occupancy-classification.md) | IBC 2009 | 2 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 2 | | [Scope and Administration](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/scope-and-administration.md) | IMC 2009 | 1 | | [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | IRC 2009 | 1 | | [Scope and Administration](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/scope-and-administration.md) | IRC 2009 | 1 | ## Hill compared with Ridge 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 | | --- | --- | | **Hill** (IRC 2009) | land, surface, horizontal, direction | | [Ridge](https://harth.build/resources/glossary/ridge.md) (IRC 2009) | elongated, crest, hill, two, directions | 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 hill and ridge. ## Hill: 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 | Commercial Energy Efficiency (IECC 2009) | | | Re-check the requirement that uses it | Building Planning (IRC 2009) | | | Re-check the requirement that uses it | Structural Design (IBC 2009) | | | Re-check the requirement that uses it | Hydronic Piping (IMC 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 hill? The International Residential Code (IRC) 2009 defines it in Definitions as: “With respect to topographic wind effects, a land surface characterized by strong relief in any horizontal direction.” 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 hill? In this corpus the term is used across 12 chapters, led by Commercial Energy Efficiency in the IECC 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 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 hill, which the IRC 2009 defines as “With respect to topographic wind effects, a land surface characterized by strong relief in any horizontal direction.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted. ### What does "hill" mean in slang? 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, a land surface characterized by strong relief in any horizontal direction.” 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%2Fhill%2F - View this page in a browser: https://harth.build/resources/glossary/hill/ - All resources for agents: https://harth.build/llms.txt