Building Code Glossary
Backflow: Building Code Definition
How the IPC 2009 define backflow, 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
Backflow is a defined term in the International Plumbing Code (IPC) 2009, in Definitions. The code's own words are: “Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.” No other I-Code in this corpus defines it, so the IPC 2009 definition is the one to work from. The term is used in 21 chapters of this corpus, most often in Water Supply and Distribution (IPC 2009), Water Supply and Distribution (IRC 2009), Fixtures, Faucets and Fixture Fittings (IPC 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?
Backflow — IPC 2009, Definitions:
Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.
What must be verified before using this guidance?
Backflow is defined once in this corpus, in the Definitions chapter of the International Plumbing Code (IPC) 2009:
Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.
Where backflow 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 |
|---|---|---|
| Water Supply and Distribution | IPC 2009 | 102 |
| Water Supply and Distribution | IRC 2009 | 80 |
| Fixtures, Faucets and Fixture Fittings | IPC 2009 | 25 |
| Definitions | IPC 2009 | 16 |
| Fire Protection Systems | IFC 2009 | 12 |
| General Regulations | IPC 2009 | 11 |
| Definitions | IRC 2009 | 10 |
| Fire Protection Systems | IBC 2009 | 9 |
| Flammable and Combustible Liquids | IFC 2009 | 9 |
| Hazardous Materials-general Provisions | IFC 2009 | 9 |
| Plumbing Administration | IRC 2009 | 6 |
| Plumbing Fixtures | IRC 2009 | 6 |
9 further chapters mention the term.
The term in use
How the code actually writes about backflow, quoted from the 2009 text hosted here:
Where a dual check-valve backflow preventer is installed on the water supply system, it shall comply with ASSE 1024 or CSA B64.6.
The supply lines and fittings for every plumbing fixture shall be installed to prevent backflow.
The supply lines and fittings for every plumbing fixture shall be installed so as to prevent backflow.
The terms backflow is built out of
The definition above leans on 1 other defined term. Each carries its own code definition, and a local amendment to any of them changes what backflow covers:
- System — IFC 2009: An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping.
Backflow: 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 IPC | Definitions | |
| Re-check the requirement that uses it | Water Supply and Distribution (IPC 2009) | |
| Re-check the requirement that uses it | Water Supply and Distribution (IRC 2009) | |
| Re-check the requirement that uses it | Fixtures, Faucets and Fixture Fittings (IPC 2009) | |
| Re-check the requirement that uses it | Definitions (IPC 2009) | |
| Confirm the dependent definition | System | |
| 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
- System: Building Code Definition
- Building: Building Code Definition
- Construction Documents: Building Code Definition
- Registered Design Professional: 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 backflow?
The International Plumbing Code (IPC) 2009 defines it in Definitions as: “Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.” 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 backflow?
In this corpus the term is used across 21 chapters, led by Water Supply and Distribution in the IPC 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 backflow in a building?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IPC 2009 states, in Definitions: “Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.” It is defined in 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.
Is a backflow preventer required by code?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IPC 2009 states, in Definitions: “Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.” It is defined in 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.
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