# Backflow Preventer, Reduced-pressure-zone Type: Building Code Definition

> How the IRC 2009 define backflow preventer, reduced-pressure-zone type, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/backflow-preventer-reduced-pressure-zone-type/
- Last updated: 2026-09-07
- Data source: 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.

## Key facts

| Fact | Value |
| --- | --- |
| Defined in | IRC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 1 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Backflow preventer, reduced-pressure-zone type is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “A backflow-prevention device consisting of two independently acting check valves, internally force loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to atmosphere internally loaded to a normally open position between two tightly closing shutoff valves and with means for …” No other I-Code in this corpus defines it, so the IRC 2009 definition is the one to work from. The term is used in 1 chapters of this corpus, most often in Definitions (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](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.*

## What does this term mean?

**Backflow Preventer, Reduced-pressure-zone Type** — IRC 2009, Definitions:

> A backflow-prevention device consisting of two independently acting check valves, internally force loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to atmosphere internally loaded to a normally open position between two tightly closing shutoff valves and with means for testing for tightness of the checks and opening of relief means.

![Labeled code-term definition diagram: Backflow Preventer, Reduced-pressure-zone Type: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/backflow-preventer-reduced-pressure-zone-type/diagram-1344.webp)

*How the IRC 2009 define backflow preventer, reduced-pressure-zone type, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Backflow Preventer, Reduced-pressure-zone Type** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) chapter of the International Residential Code (IRC) 2009:

> A backflow-prevention device consisting of two independently acting check valves, internally force loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to atmosphere internally loaded to a normally open position between two tightly closing shutoff valves and with means for testing for tightness of the checks and opening of relief means.

## Where backflow preventer, reduced-pressure-zone type is used in the code

The term appears in 1 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 |

## The terms backflow preventer, reduced-pressure-zone type is built out of

The definition above leans on 4 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what backflow preventer, reduced-pressure-zone type covers:

- **[Automatic](https://harth.build/resources/glossary/automatic.md)** — IBC 2009: As applied to fire protection devices, a device or system providing an emergency function without the necessity for human intervention and activated as a result of a predetermined temperature rise, rate of temperature rise or combustion products.
- **[Backflow](https://harth.build/resources/glossary/backflow.md)** — 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.
- **[Venting](https://harth.build/resources/glossary/venting.md)** — IRC 2009: Removal of combustion products to the outdoors.
- **[Device](https://harth.build/resources/glossary/device.md)** — IRC 2009: Aunit of an electrical system that carries or controls electrical energy as it principal function.

## Backflow Preventer, Reduced-pressure-zone Type: what to open, and in what order

Every row is a document this term depends on. The [ICC code library](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) cover the middle rows.

| Check | Where | Confirmed |
| --- | --- | --- |
| Read the definition in the adopted IRC | Definitions | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| Confirm the dependent definition | Automatic | |
| Confirm the dependent definition | Backflow | |
| Confirm the dependent definition | Venting | |
| 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](https://harth.build/resources/glossary.md)
- [Automatic: Building Code Definition](https://harth.build/resources/glossary/automatic.md)
- [Backflow: Building Code Definition](https://harth.build/resources/glossary/backflow.md)
- [Venting: Building Code Definition](https://harth.build/resources/glossary/venting.md)
- [Device: Building Code Definition](https://harth.build/resources/glossary/device.md)

## 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](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.

### Source links

- [codes.iccsafe.org](https://codes.iccsafe.org/codes)

- [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/)

## Frequently asked questions

### What is the code definition of backflow preventer, reduced-pressure-zone type?

The International Residential Code (IRC) 2009 defines it in Definitions as: “A backflow-prevention device consisting of two independently acting check valves, internally force loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to atmosphere internally loaded to a normally open position between two tightly closing shutoff valves and with means for testing for tightness of the checks and opening of relief means.” 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 preventer, reduced-pressure-zone type?

In this corpus the term is used across 1 chapters, led by Definitions 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 a reduced pressure zone backflow preventer?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A backflow-prevention device consisting of two independently acting check valves, internally force loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to atmosphere internally loaded to a normally open position between two tightly closing shutoff valves and with means for …” It is defined in IRC 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 a backflow preventer with pressure reducing valve?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A backflow-prevention device consisting of two independently acting check valves, internally force loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to atmosphere internally loaded to a normally open position between two tightly closing shutoff valves and with means for …” It is defined in IRC 2009. It is not the same as Valve, which the IRC 2009 defines separately as “A device used in piping to control the gas supply to any section of a system of piping or to an appliance.” 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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