Building Code Glossary
Trap Seal: Building Code Definition
How the IRC 2009, IPC 2009 define trap seal, 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
Trap seal is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap.” The IPC 2009 defines the same term with different wording, so the controlling text depends on which code governs the question in front of you — the comparison below sets the versions side by side. The term is used in 11 chapters of this corpus, most often in Traps, Interceptors and Separators (IPC 2009), Traps (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.
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?
Trap Seal — IRC 2009, Definitions:
The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap.
What must be verified before using this guidance?
Two of the I-Codes in this corpus define Trap Seal, and the wording is not identical — read the version that governs your question.
| Code | Where it is defined | Definition |
|---|---|---|
| IRC 2009 | Definitions | The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap. |
| IPC 2009 | Definitions | The vertical distance between the weir and the top of the dip of the trap. |
Where trap seal is used in the code
The term appears in 11 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Traps, Interceptors and Separators | IPC 2009 | 9 |
| Traps | IRC 2009 | 6 |
| Fixtures, Faucets and Fixture Fittings | IPC 2009 | 5 |
| Definitions | IRC 2009 | 5 |
| Definitions | IPC 2009 | 4 |
| Sanitary Drainage | IPC 2009 | 4 |
| Indirect/special Waste | IPC 2009 | 2 |
| Vents | IRC 2009 | 2 |
| Vents | IPC 2009 | 1 |
| Water Supply and Distribution | IPC 2009 | 1 |
| Plumbing Fixtures | IRC 2009 | 1 |
The term in use
How the code actually writes about trap seal, quoted from the 2009 text hosted here:
Slip joints shall be made with an approved elastomeric gasket and shall be installed only on the trap inlet, trap outlet and within the trap seal.
Solid connections, slipjoints and couplings are permitted to be used on the trap inlet, trap outlet, or within the trap seal.
Water closets having a concealed trap seal or an unventilated space or having walls that are not thoroughly washed at each discharge in accordance with ASME AI12.19.2M shall be prohibited.
The terms trap seal 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 trap seal covers:
- Liquid — IBC 2009: A material that has a melting point that is equal to or less than 68°F (20°C) and a boiling point that is greater than 68°F (20°C) at 14.7 pounds per square inch absolute (psia) (101 kPa).
Trap Seal: 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 | Traps, Interceptors and Separators (IPC 2009) | |
| Re-check the requirement that uses it | Traps (IRC 2009) | |
| Re-check the requirement that uses it | Fixtures, Faucets and Fixture Fittings (IPC 2009) | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| Confirm the dependent definition | Liquid | |
| 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
- Liquid: 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 trap seal?
The International Residential Code (IRC) 2009 defines it in Definitions as: “The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap.” 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 trap seal?
In this corpus the term is used across 11 chapters, led by Traps, Interceptors and Separators 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 are the building code requirements for trap seals?
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 trap seal, which the IRC 2009 defines as “The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
What is the definition of a trap seal?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap.” 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.
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