Building Code Glossary
Existing Structure: Building Code Definition
How the IBC 2009 define existing structure, 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
Existing structure is a defined term in the International Building Code (IBC) 2009, in Existing Structures. The code's own words are: “A structure erected prior to the date of adoption of the appropriate code, or one for which a legal building permit has been issued.” No other I-Code in this corpus defines it, so the IBC 2009 definition is the one to work from. The term is used in 21 chapters of this corpus, most often in Existing Structures (IBC 2009), Scope and Administration (IRC 2009), Scope and Administration (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, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Existing Structure — IBC 2009, Existing Structures:
A structure erected prior to the date of adoption of the appropriate code, or one for which a legal building permit has been issued.
What must be verified before using this guidance?
Existing Structure is defined once in this corpus, in the Existing Structures chapter of the International Building Code (IBC) 2009:
A structure erected prior to the date of adoption of the appropriate code, or one for which a legal building permit has been issued.
Where existing structure is used in the code
The term appears in 21 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 | 23 |
| Scope and Administration | IRC 2009 | 9 |
| Scope and Administration | IBC 2009 | 7 |
| Accessibility | IBC 2009 | 4 |
| Scope and Administration | IFC 2009 | 4 |
| Structural Design | IBC 2009 | 3 |
| Flammable and Combustible Liquids | IFC 2009 | 3 |
| Foundations | IRC 2009 | 3 |
| Definitions | IBC 2009 | 2 |
| General Building Heights and Areas | IBC 2009 | 2 |
| Structural Tests and Special Inspections | IBC 2009 | 2 |
| Fire Protection Systems | IFC 2009 | 2 |
9 further chapters mention the term.
The term in use
How the code actually writes about existing structure, quoted from the 2009 text hosted here:
For buildings and structures in flood hazard areas established in Section 1612.3, any addition that constitutes substantial improvement of the existing structure, as defined in Section 1612.2, shall comply with the flood design requirements for new construction, and all aspects of the existing structure shall be brought into compliance with the requirements for new construction for flood design.
Additions, alterations or repairs to any structure shall conform to the requirements for a new structure without requiring the existing structure to comply with all of the requirements of this code, unless otherwise stated.
Subject to the approval of the fire code official, the use or occupancy of an existing structure shall be allowed to be changed and the structure is allowed to be occupied for purposes in other groups without conforming to all the requirements of this code and the International BUilding Code for those groups, provided the new or proposed use is …
Existing Structure compared with Building, Existing
These two are the closest pair in the 2009 I-Codes: about 75 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 | |
|---|---|
| Existing Structure (IBC 2009) | structure, date, appropriate |
| Building, Existing (IRC 2009) | existing |
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 existing structure and building, existing.
The terms existing structure 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 existing structure covers:
- 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.
- Permit — IBC 2009: An official document or certificate issued by the authority having jurisdiction which authorizes performance of a specified activity.
Existing Structure: 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 | Existing Structures | |
| Re-check the requirement that uses it | Existing Structures (IBC 2009) | |
| Re-check the requirement that uses it | Scope and Administration (IRC 2009) | |
| Re-check the requirement that uses it | Scope and Administration (IBC 2009) | |
| Re-check the requirement that uses it | Accessibility (IBC 2009) | |
| Confirm the dependent definition | Structure | |
| Confirm the dependent definition | Building | |
| Confirm the dependent definition | Permit | |
| 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
- Structure: Building Code Definition
- Building: Building Code Definition
- Permit: 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 existing structure?
The International Building Code (IBC) 2009 defines it in Existing Structures as: “A structure erected prior to the date of adoption of the appropriate code, or one for which a legal building permit has been issued.” 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 existing structure?
In this corpus the term is used across 21 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 an existing structure?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Existing Structures: “A structure erected prior to the date of adoption of the appropriate code, or one for which a legal building permit has been issued.” It is defined in IBC 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 considered a structure in 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 existing structure, which the IBC 2009 defines as “A structure erected prior to the date of adoption of the appropriate code, or one for which a legal building permit has been issued.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
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