Building Code Glossary
Building Subdrain: Building Code Definition
How the IPC 2009 define building subdrain, 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
Building subdrain is a defined term in the International Plumbing Code (IPC) 2009, in Definitions. The code's own words are: “That portion of a drainage system that does not drain by gravity into the bUilding sewer.” 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 3 chapters of this corpus, most often in Storm Drainage (IPC 2009), Sanitary Drainage (IPC 2009), Definitions (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?
Building Subdrain — IPC 2009, Definitions:
That portion of a drainage system that does not drain by gravity into the bUilding sewer.
What must be verified before using this guidance?
Building Subdrain is defined once in this corpus, in the Definitions chapter of the International Plumbing Code (IPC) 2009:
That portion of a drainage system that does not drain by gravity into the bUilding sewer.
Where building subdrain 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 |
|---|---|---|
| Storm Drainage | IPC 2009 | 3 |
| Sanitary Drainage | IPC 2009 | 2 |
| Definitions | IPC 2009 | 1 |
The terms building subdrain 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 building subdrain covers:
- Drainage System — IPC 2009: Piping within a public or private premise that conveys sewage, rainwater or other liquid wastes to a point of disposal.
- Building Sewer — IRC 2009: That part of the drainage system that extends from the end of the building drain and conveys its discharge to a public sewer, private sewer, individual sewage-diSposal system or other point of disposal.
- Building — IBC 2009: Any structure used or intended for supporting or sheltering any use or occupancy.
- System — IFC 2009: An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping.
- Drain — IRC 2009: Any pipe that carries soil and water-borne wastes in a building drainage system.
Building Subdrain: 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 | Storm Drainage (IPC 2009) | |
| Re-check the requirement that uses it | Sanitary Drainage (IPC 2009) | |
| Re-check the requirement that uses it | Definitions (IPC 2009) | |
| Confirm the dependent definition | Drainage System | |
| Confirm the dependent definition | Building Sewer | |
| 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
- Drainage System: Building Code Definition
- Building Sewer: Building Code Definition
- Building: Building Code Definition
- System: 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 building subdrain?
The International Plumbing Code (IPC) 2009 defines it in Definitions as: “That portion of a drainage system that does not drain by gravity into the bUilding sewer.” 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 building subdrain?
In this corpus the term is used across 3 chapters, led by Storm Drainage 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 the plumbing code for shower drains?
Plumbing is a separate defined term. The IRC 2009 defines it as: “For the purpose of this code, plumbing refers to those installations, repairs, maintenance and alterations regulated by Chapters 25 through 33.” That is not the same as building subdrain, which the IPC 2009 defines as “That portion of a drainage system that does not drain by gravity into the bUilding sewer.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
What is a building subdrain?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IPC 2009 states, in Definitions: “That portion of a drainage system that does not drain by gravity into the bUilding sewer.” 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.
Related pages
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- Building Sewer: Building Code Definition
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- Building: Building Code Definition
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