Building Code Glossary
Addition: Building Code Definition
How the IBC 2009, IRC 2009, IECC 2009 define addition, 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
Addition is a defined term in the International Building Code (IBC) 2009, in Definitions. The code's own words are: “An extension or increase in floor area or height of a building or structure.” The IRC 2009 words it differently, in Definitions: “An extension or increase in floor area or height of a building or structure.” The IRC 2009, IECC 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 128 chapters of this corpus, most often in Existing Structures (IBC 2009), Building Planning (IRC 2009), Wall Construction (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?
Addition — IBC 2009, Definitions:
An extension or increase in floor area or height of a building or structure.
What must be verified before using this guidance?
Three of the I-Codes in this corpus define Addition, and the wording is not identical — read the version that governs your question.
| Code | Where it is defined | Definition |
|---|---|---|
| IBC 2009 | Definitions | An extension or increase in floor area or height of a building or structure. |
| IRC 2009 | Definitions | An extension or increase in floor area or height of a building or structure. |
| IECC 2009 | Definitions | An extension or increase in the conditioned space floor area or height of a building or structure. |
Where addition is used in the code
The term appears in 128 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Existing Structures | IBC 2009 | 61 |
| Building Planning | IRC 2009 | 47 |
| Wall Construction | IRC 2009 | 42 |
| Wood | IBC 2009 | 39 |
| Fire Protection Systems | IFC 2009 | 38 |
| Means of Egress | IFC 2009 | 34 |
| Means of Egress | IBC 2009 | 32 |
| Commercial Energy Efficiency | IECC 2009 | 31 |
| Fuel Gas | IRC 2009 | 31 |
| Special Detailed Requirements Based on Use and Occupancy | IBC 2009 | 29 |
| Water Supply and Distribution | IRC 2009 | 28 |
| Soils and Foundations | IBC 2009 | 27 |
116 further chapters mention the term.
The term in use
How the code actually writes about addition, quoted from the 2009 text hosted here:
The provisions of this chapter shall control the alteration, repair, addition and change of occupancy of existing structures.
Alterations resulting in the addition of loads to any member (e.g., HVAC equipment, waterheaters) shall not be permitted without verification that the truss is capable of supporting such additional loading.
nor shall ordinary repairs include addition to, alteration of, replacement or relocation ofany water supply, sewer, drainage, drain leader, gas, soil, waste, vent or similar piping, electric wiring or mechanical or other work affecting public health or general safety.
The terms addition 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 addition 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 …
- Structure — IPC 2009: That which is built or constructed or a portion thereof.
- Building — IBC 2009: Any structure used or intended for supporting or sheltering any use or occupancy.
Addition: 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 | Definitions | |
| Read the definition in the adopted IRC | Definitions | |
| Read the definition in the adopted IECC | Definitions | |
| Re-check the requirement that uses it | Existing Structures (IBC 2009) | |
| Re-check the requirement that uses it | Building Planning (IRC 2009) | |
| Re-check the requirement that uses it | Wall Construction (IRC 2009) | |
| Re-check the requirement that uses it | Wood (IBC 2009) | |
| Confirm the dependent definition | Conditioned Space | |
| Confirm the dependent definition | Structure | |
| 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
- Conditioned Space: Building Code Definition
- Structure: Building Code Definition
- Building: 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 addition?
The International Building Code (IBC) 2009 defines it in Definitions as: “An extension or increase in floor area or height of a building or structure.” 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 addition the same way?
No. IBC 2009, 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 addition?
In this corpus the term is used across 128 chapters, led by Existing 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 a building addition?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Definitions: “An extension or increase in floor area or height of a building or structure.” It is defined in IBC 2009, IRC 2009, IECC 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 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 addition, which the IBC 2009 defines as “An extension or increase in floor area or height of a building or structure.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
What is the abbreviation for addition?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Definitions: “An extension or increase in floor area or height of a building or structure.” It is defined in IBC 2009, IRC 2009, IECC 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.
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