Updated 2026-09-07

Building Code Glossary

Duct: Building Code Definition

How the IMC 2009, IECC 2009 define duct, where the wording differs, and which chapters depend on the term.

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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.

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Direct answer

Duct is a defined term in the International Mechanical Code (IMC) 2009, in Definitions. The code's own words are: “A tube or conduit utilized for conveying air. The air passages of self-contained systems are not to be construed as air ducts.” The IECC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 129 chapters of this corpus, most often in Exhaust Systems (IMC 2009), Duct Systems (IMC 2009), Fire and Smoke Protection Features (IBC 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?

Duct — IMC 2009, Definitions:

A tube or conduit utilized for conveying air. The air passages of self-contained systems are not to be construed as air ducts.

Labeled code-term definition diagram: Duct: Building Code Definition — How the IMC 2009, IECC 2009 define duct, where the wording differs, and which chapters depend on the term.

What must be verified before using this guidance?

Two of the I-Codes in this corpus define Duct, in identical words.

Code	Where it is defined	Definition
IMC 2009	Definitions	A tube or conduit utilized for conveying air. The air passages of self-contained systems are not to be construed as air ducts.
IECC 2009	Definitions	A tube or conduit utilized for conveying air. The air passages of self-contained systems are not to be construed as air ducts.

Where duct is used in the code

The term appears in 129 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

Chapter	Code	Mentions
Exhaust Systems	IMC 2009	537
Duct Systems	IMC 2009	388
Fire and Smoke Protection Features	IBC 2009	303
Services	IRC 2009	250
Power and Lighting Distribution	IRC 2009	221
Fuel Gas	IRC 2009	215
Fire Protection Systems	IBC 2009	176
Flammable and Combustible Liquids	IFC 2009	155
Branch Circuit and Feeder Requirements	IRC 2009	153
Duct Systems	IRC 2009	145
Fire Protection Systems	IFC 2009	140
Special Detailed Requirements Based on Use and Occupancy	IBC 2009	131

117 further chapters mention the term.

The term in use

How the code actually writes about duct, quoted from the 2009 text hosted here:

Where exhaust duct construction is not specified in this chapter, such construction shall comply with Chapter 6.

— IMC 2009 §501.4

Duct systems used for the movement of air in air-conditioning, heating, ventilating and exhaust systems shall conform to the provisions of this chapter except as otherwise specified in Chapters 5 and 7.

— IMC 2009 §601.1

Any duct system that is part of the pressurization system shall be protected with the same fire-resistance rating as required for the elevator shaft enclosure.

— IBC 2009 §708.14.2.3

Duct: 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 IMC	Definitions
Read the definition in the adopted IECC	Definitions
Re-check the requirement that uses it	Exhaust Systems (IMC 2009)
Re-check the requirement that uses it	Duct Systems (IMC 2009)
Re-check the requirement that uses it	Fire and Smoke Protection Features (IBC 2009)
Re-check the requirement that uses it	Services (IRC 2009)
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.

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 duct?

The International Mechanical Code (IMC) 2009 defines it in Definitions as: “A tube or conduit utilized for conveying air. The air passages of self-contained systems are not to be construed as air ducts.” 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.

Do the I-Codes define duct the same way?

In the 2009 editions transcribed here, yes: IMC 2009, IECC 2009 carry the same wording, so the term means the same thing in each. Later editions do diverge on some terms, so confirm against the adopted edition rather than assuming the alignment holds.

Which parts of the code depend on duct?

In this corpus the term is used across 129 chapters, led by Exhaust Systems in the IMC 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 duct in a building?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IMC 2009 states, in Definitions: “A tube or conduit utilized for conveying air. The air passages of self-contained systems are not to be construed as air ducts.” It is defined in IMC 2009, IECC 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.

What are the code requirements for duct insulation?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IMC 2009 states, in Definitions: “A tube or conduit utilized for conveying air. The air passages of self-contained systems are not to be construed as air ducts.” It is defined in IMC 2009, IECC 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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