Building Code Glossary
Combination Waste and Vent System: Building Code Definition
How the IRC 2009, IPC 2009 define combination waste and vent system, 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
Combination waste and vent system is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “A specially designed system of waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the drain.” The IPC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 3 chapters of this corpus, most often in Vents (IRC 2009), Definitions (IPC 2009), 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, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Combination Waste and Vent System — IRC 2009, Definitions:
A specially designed system of waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the drain.
What must be verified before using this guidance?
Two of the I-Codes in this corpus define Combination Waste and Vent System, in identical words.
| Code | Where it is defined | Definition |
|---|---|---|
| IRC 2009 | Definitions | A specially designed system of waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the drain. |
| IPC 2009 | Definitions | A specially designed system of waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the drain. |
Where combination waste and vent system is used in the code
The term appears in 3 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Vents | IRC 2009 | 4 |
| Definitions | IPC 2009 | 1 |
| Definitions | IRC 2009 | 1 |
The term in use
How the code actually writes about combination waste and vent system, quoted from the 2009 text hosted here:
A combination waste and vent system shall not serve fixtures other than floor drains, sinks and lavatories.
The terms combination waste and vent system 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 combination waste and vent system covers:
- Venting — IRC 2009: Removal of combustion products to the outdoors.
- Piping — IRC 2009: Where used in this code, “piping” refers to either pipe or tubing, or both.
- System — IFC 2009: An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping.
- Waste — IRC 2009: Liquid-borne waste that is free of fecal matter.
- Drain — IRC 2009: Any pipe that carries soil and water-borne wastes in a building drainage system.
Combination Waste and Vent System: 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 IRC | Definitions | |
| Read the definition in the adopted IPC | Definitions | |
| Re-check the requirement that uses it | Vents (IRC 2009) | |
| Re-check the requirement that uses it | Definitions (IPC 2009) | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| Confirm the dependent definition | Venting | |
| Confirm the dependent definition | Piping | |
| 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
- Venting: Building Code Definition
- System: Building Code Definition
- Piping: Building Code Definition
- Waste: 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 combination waste and vent system?
The International Residential Code (IRC) 2009 defines it in Definitions as: “A specially designed system of waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the drain.” 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 combination waste and vent system?
In this corpus the term is used across 3 chapters, led by Vents 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 does a combination waste and vent system mean?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A specially designed system of waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the drain.” It is defined in IRC 2009, 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.
What is a combination waste and vent system in plumbing?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A specially designed system of waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the drain.” It is defined in IRC 2009, IPC 2009. It is not the same as Plumbing, which the IRC 2009 defines separately as “For the purpose of this code, plumbing refers to those installations, repairs, maintenance and alterations regulated by Chapters 25 through 33.” 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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