Building Code Glossary
Basement: Building Code Definition
How the IBC 2009, IRC 2009, IFC 2009 define basement, 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 is a defined term in the International Building Code (IBC) 2009, in General Building Heights and Areas. The code's own words are: “A story that is not a storyabovegrade plane (see "Story above grade plane" in Section 202).” The IRC 2009, IFC 2009 define 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 61 chapters of this corpus, most often in Foundations (IRC 2009), Building Planning (IRC 2009), Fire Protection Systems (IBC 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 — IBC 2009, General Building Heights and Areas:
A story that is not a storyabovegrade plane (see "Story above grade plane" in Section 202).
What must be verified before using this guidance?
Three of the I-Codes in this corpus define Basement, and the wording is not identical — read the version that governs your question.
| Code | Where it is defined | Definition |
|---|---|---|
| IBC 2009 | General Building Heights and Areas | A story that is not a storyabovegrade plane (see "Story above grade plane" in Section 202). |
| IRC 2009 | Definitions | That portion of a building that is partly or completely below grade (see "Story above grade"). |
| IFC 2009 | Definitions | A story that is not a story above grade plane. |
Where basement is used in the code
The term appears in 61 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 | 58 |
| Building Planning | IRC 2009 | 43 |
| Fire Protection Systems | IBC 2009 | 31 |
| Fire Protection Systems | IFC 2009 | 30 |
| Flammable and Combustible Liquids | IFC 2009 | 26 |
| Special Detailed Requirements Based on Use and Occupancy | IBC 2009 | 19 |
| Soils and Foundations | IBC 2009 | 16 |
| Structural Design | IBC 2009 | 14 |
| Means of Egress | IBC 2009 | 13 |
| Exhaust Systems | IMC 2009 | 13 |
| Energy Efficiency | IRC 2009 | 13 |
| Liquefied Petroleum Gases | IFC 2009 | 12 |
49 further chapters mention the term.
The term in use
How the code actually writes about basement, quoted from the 2009 text hosted here:
Fasteners used below grade to attach plywood to the exterior side of exterior basement or crawl-space wall studs, or fasteners used in knee wall construction, shall be of Type 304 or 316 stainless steel.
Exterior stairways providing access to a basement from the outside grade level shall be provided with an artificial light source located in the immediate vicinity of the bottom landing of the stairway.
Where any portion of a basement is located more than 75 feet (22 860 mm) from openings required by Section 903.2.11.1, the basement shall be equipped throughout with an approved automatic sprinkler system.
The terms basement is built out of
The definition above leans on 5 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what basement covers:
- Story Above Grade Plane — IBC 2009: Any story having its finished floor surface entirely above grade plane, or in which the finished surface of the floor next above is:
- Grade Plane — IBC 2009: A reference plane representing the average of finished ground level adjoining the building at exterior walls.
- Building — IBC 2009: Any structure used or intended for supporting or sheltering any use or occupancy.
- Story — IBC 2009: That portion ofa building included between the upper surface of a floor and the upper surface of the floor or roof next above (also see "Basement," "Mezzanine" and Section 502.1).
- Grade — IRC 2009: The finished ground level adjoining the building at all exterior walls.
Basement: 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 IBC | General Building Heights and Areas | |
| Read the definition in the adopted IRC | Definitions | |
| Read the definition in the adopted IFC | Definitions | |
| Re-check the requirement that uses it | Foundations (IRC 2009) | |
| Re-check the requirement that uses it | Building Planning (IRC 2009) | |
| Re-check the requirement that uses it | Fire Protection Systems (IBC 2009) | |
| Re-check the requirement that uses it | Fire Protection Systems (IFC 2009) | |
| Confirm the dependent definition | Story Above Grade Plane | |
| Confirm the dependent definition | Grade Plane | |
| Confirm the dependent definition | Building | |
| 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
- Story Above Grade Plane: Building Code Definition
- Grade Plane: Building Code Definition
- Building: Building Code Definition
- Story: 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?
The International Building Code (IBC) 2009 defines it in General Building Heights and Areas as: “A story that is not a storyabovegrade plane (see "Story above grade plane" in Section 202).” 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 basement?
In this corpus the term is used across 61 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 legal definition of a basement?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in General Building Heights and Areas: “A story that is not a storyabovegrade plane (see "Story above grade plane" in Section 202).” It is defined in IBC 2009, IRC 2009, IFC 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.
Is a basement considered a story in IBC?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in General Building Heights and Areas: “A story that is not a storyabovegrade plane (see "Story above grade plane" in Section 202).” It is defined in IBC 2009, IRC 2009, IFC 2009. It is not the same as Story, which the IBC 2009 defines separately as “That portion ofa building included between the upper surface of a floor and the upper surface of the floor or roof next above (also see "Basement," "Mezzanine" and Section 502.1). It is measured as the …” 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 basement, which the IBC 2009 defines as “A story that is not a storyabovegrade plane (see "Story above grade plane" in Section 202).” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
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