Building Code Glossary
Basement Wall: Building Code Definition
How the IRC 2009, IECC 2009 define basement wall, 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
Basement wall is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The opaque portion of a wall that encloses one side of a basement and has an average below grade wall area that is 50 percent or more of the total opaque and non-opaque area of that enclosing side.” The IECC 2009 defines the same term with different wording, so the controlling text depends on which code governs the question in front of you — the comparison below sets the versions side by side. The term is used in 13 chapters of this corpus, most often in Foundations (IRC 2009), Definitions (IECC 2009), Energy Efficiency (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?
Basement Wall — IRC 2009, Definitions:
The opaque portion of a wall that encloses one side of a basement and has an average below grade wall area that is 50 percent or more of the total opaque and non-opaque area of that enclosing side.
What must be verified before using this guidance?
Two of the I-Codes in this corpus define Basement Wall, and the wording is not identical — read the version that governs your question.
| Code | Where it is defined | Definition |
|---|---|---|
| IRC 2009 | Definitions | The opaque portion of a wall that encloses one side of a basement and has an average below grade wall area that is 50 percent or more of the total opaque and non-opaque area of that enclosing side. |
| IECC 2009 | Definitions | A wall 50 percent or more below grade and enclosing conditioned space. |
Where basement wall is used in the code
The term appears in 13 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Foundations | IRC 2009 | 33 |
| Definitions | IECC 2009 | 7 |
| Energy Efficiency | IRC 2009 | 7 |
| Residential Energy Efficiency | IECC 2009 | 5 |
| Concrete | IBC 2009 | 4 |
| Definitions | IRC 2009 | 3 |
| Plastic | IBC 2009 | 2 |
| Soils and Foundations | IBC 2009 | 2 |
| Climate Zones | IECC 2009 | 2 |
| Building Planning | IRC 2009 | 2 |
| Wall Construction | IRC 2009 | 2 |
| Encroachments Into the Public Right-of-way | IBC 2009 | 1 |
1 further chapters mention the term.
The term in use
How the code actually writes about basement wall, quoted from the 2009 text hosted here:
The certificate shall list the predominant R-values of insulation installed in or on ceiling/roof, walls, foundation (slab, basement wall, crawlspace wall and/or floor) and ducts outside conditionedspaces;
Walls associated with conditioned basements shall be insulated from the top of the basement wall down to 10 feet (3048 mm) below grade or to the basement floor, whichever is less.
Where a basement is considered a story above grade plane and the finished ground level adjacent to the basement wall is below the basement floor elevation for 25 percent or more of the perimeter, the floor and walls shall be dampproofed in accordance with Section 1805.2 and a foundation drain shall be installed in accordance with Section 1805.4.2.
Basement Wall compared with Crawl Space Wall
These two are the closest pair in the 2009 I-Codes: about 45 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 | |
|---|---|
| Basement Wall (IRC 2009) | one, side, basement, average, area, 50, percent, more, total, non, enclosing |
| Crawl Space Wall (IECC 2009) | crawl, space, partially, totally |
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 basement wall and crawl space wall.
The terms basement wall is built out of
The definition above leans on 3 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what basement wall covers:
- Conditioned Space — IRC 2009: For energy purposes, space within a building that is provided with heating and/or cooling equipmentor systems capable of maintaining, through design or heat loss/gain, 50°F (IO°C) during the heating season and 85°F (29°C) during the cooling season, or communicates directly …
- Basement — IBC 2009: A story that is not a storyabovegrade plane (see "Story above grade plane" in Section 202).
- Grade — IRC 2009: The finished ground level adjoining the building at all exterior walls.
Basement Wall: 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 IECC | Definitions | |
| Re-check the requirement that uses it | Foundations (IRC 2009) | |
| Re-check the requirement that uses it | Definitions (IECC 2009) | |
| Re-check the requirement that uses it | Energy Efficiency (IRC 2009) | |
| Re-check the requirement that uses it | Residential Energy Efficiency (IECC 2009) | |
| Confirm the dependent definition | Conditioned Space | |
| Confirm the dependent definition | Basement | |
| Confirm the dependent definition | Grade | |
| 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
- Conditioned Space: Building Code Definition
- Basement: Building Code Definition
- Grade: 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 basement wall?
The International Residential Code (IRC) 2009 defines it in Definitions as: “The opaque portion of a wall that encloses one side of a basement and has an average below grade wall area that is 50 percent or more of the total opaque and non-opaque area of that enclosing side.” 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.
Do the I-Codes define basement wall the same way?
No. IRC 2009, IECC 2009 all define the term, but the wording is not identical, and a difference in wording can change which requirements are triggered. The comparison table above sets the versions side by side so you can read the one that governs your question.
Which parts of the code depend on basement wall?
In this corpus the term is used across 13 chapters, led by Foundations 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 IRC code minimum for grade away from a foundation wall?
Grade is a separate defined term. The IRC 2009 defines it as: “The finished ground level adjoining the building at all exterior walls.” That is not the same as basement wall, which the IRC 2009 defines as “The opaque portion of a wall that encloses one side of a basement and has an average below grade wall area that is 50 percent or more of the total opaque and non-opaque area of that enclosing side.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
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