Building Code Glossary
Slope: Building Code Definition
How the IRC 2009, IPC 2009 define slope, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · 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.
Direct answer
Slope is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The fall (pitch) of a line of pipe in reference to a horizontal plane. In drainage, the slope is expressed as the fall in units vertical per units horizontal (percent) for a length of pipe.” The IPC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 63 chapters of this corpus, most often in Roof Assemblies and Rooftop Structures (IBC 2009), Roof Assemblies (IRC 2009), Foundations (IRC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.
Content and cited inputs reviewed by Scott Barrington, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Slope — IRC 2009, Definitions:
The fall (pitch) of a line of pipe in reference to a horizontal plane. In drainage, the slope is expressed as the fall in units vertical per units horizontal (percent) for a length of pipe.
What must be verified before using this guidance?
Two of the I-Codes in this corpus define Slope, in identical words.
| Code | Where it is defined | Definition |
|---|---|---|
| IRC 2009 | Definitions | The fall (pitch) of a line of pipe in reference to a horizontal plane. In drainage, the slope is expressed as the fall in units vertical per units horizontal (percent) for a length of pipe. |
| IPC 2009 | Definitions | The fall (pitch) of a line of pipe in reference to a horizontal plane. In drainage, the slope is expressed as the fall in units vertical per units horizontal (percent) for a length of pipe. |
Where slope is used in the code
The term appears in 63 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 Assemblies and Rooftop Structures | IBC 2009 | 210 |
| Roof Assemblies | IRC 2009 | 153 |
| Foundations | IRC 2009 | 80 |
| Means of Egress | IBC 2009 | 72 |
| Means of Egress | IFC 2009 | 72 |
| Soils and Foundations | IBC 2009 | 71 |
| Building Planning | IRC 2009 | 65 |
| Glass and Glazing | IBC 2009 | 53 |
| Mound Systems | IPC 2009 | 47 |
| Roof-ceiling Construction | IRC 2009 | 35 |
| Site Evaluation and Requirements | IPC 2009 | 34 |
| General Regulations | IMC 2009 | 18 |
51 further chapters mention the term.
The term in use
How the code actually writes about slope, quoted from the 2009 text hosted here:
Flashing shall be installed at wall and roof intersections, at gutters, wherever there is a change in roof slope or direction and around roof openings.
Flashings shall be installed at wall and roof intersections, wherever there is a change in roof slope or direction and around roof openings.
The bottom surface of footings shall not have a slope exceeding one unit vertical in 10 units horizontal (10-percent slope).
Slope: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IRC | Definitions | |
| Read the definition in the adopted IPC | Definitions | |
| Re-check the requirement that uses it | Roof Assemblies and Rooftop Structures (IBC 2009) | |
| Re-check the requirement that uses it | Roof Assemblies (IRC 2009) | |
| Re-check the requirement that uses it | Foundations (IRC 2009) | |
| Re-check the requirement that uses it | Means of Egress (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
- Building: Building Code Definition
- Construction Documents: Building Code Definition
- Registered Design Professional: Building Code Definition
- Dwelling Unit: Building Code Definition
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 publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of slope?
The International Residential Code (IRC) 2009 defines it in Definitions as: “The fall (pitch) of a line of pipe in reference to a horizontal plane. In drainage, the slope is expressed as the fall in units vertical per units horizontal (percent) for a length of pipe.” 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 slope?
In this corpus the term is used across 63 chapters, led by Roof Assemblies and Rooftop Structures 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 definition of a slope in construction?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “The fall (pitch) of a line of pipe in reference to a horizontal plane. In drainage, the slope is expressed as the fall in units vertical per units horizontal (percent) for a length of pipe.” It is defined in IRC 2009, IPC 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 the building code acceptable slope for a deck?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “The fall (pitch) of a line of pipe in reference to a horizontal plane. In drainage, the slope is expressed as the fall in units vertical per units horizontal (percent) for a length of pipe.” It is defined in IRC 2009, IPC 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.
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