# Fenestration: Building Code Definition

> How the IRC 2009, IECC 2009 define fenestration, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/fenestration/
- 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, IECC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 11 (counted across the codes hosted here) |
| Wording identical across codes | No (compare before citing one code's wording under another) |

## Direct answer

Fenestration is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “Skylights, roof windows, vertical windows (whether fixed or moveable); opaque doors; glazed doors; glass block; and combination opaque/glazed doors.” The IECC 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 Residential Energy Efficiency (IECC 2009), Energy Efficiency (IRC 2009), Commercial Energy Efficiency (IECC 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?

**Fenestration** — IRC 2009, Definitions:

> Skylights, roof windows, vertical windows (whether fixed or moveable); opaque doors; glazed doors; glass block; and combination opaque/glazed doors.

![Labeled code-term definition diagram: Fenestration: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/fenestration/diagram-1344.webp)

*How the IRC 2009, IECC 2009 define fenestration, 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 **Fenestration**, and the wording is not identical — read the version that governs your question.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IRC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | Skylights, roof windows, vertical windows (whether fixed or moveable); opaque doors; glazed doors; glass block; and combination opaque/glazed doors. |
| IECC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) | Skylights, roof windows, vertical windows (fixed or moveable), opaque doors, glazed doors, glazed block and combination opaque/glazed doors. Fenestration includes products with glass and nonglass glazing materials. |

## Where fenestration 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 |
| --- | --- | --- |
| [Residential Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/residential-energy-efficiency.md) | IECC 2009 | 33 |
| [Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/energy-efficiency.md) | IRC 2009 | 30 |
| [Commercial Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/commercial-energy-efficiency.md) | IECC 2009 | 18 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) | IECC 2009 | 12 |
| [Wall Construction](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md) | IRC 2009 | 8 |
| [Climate Zones](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/climate-zones.md) | IECC 2009 | 6 |
| [Administration](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/administration.md) | IECC 2009 | 4 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 4 |
| [Scope and Administration](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/scope-and-administration.md) | IBC 2009 | 2 |
| [Building Planning](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md) | IRC 2009 | 2 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 1 |

### The term in use

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

> U-factors for fenestration and the solar heat gain coefficient (SHGC) of fenestration.

— [IECC 2009 §401.3](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/residential-energy-efficiency.md)

> V-factors of fenestration products (windows, doors and skylights) shall be determined in accordance with NFRC 100 by an accredited, independent laboratory, and labeled and certified by the manufacturer.

— [IRC 2009 §N1101.5](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/energy-efficiency.md)

> Buildings with a vertical fenestration area or skylight area that exceeds that allowed in Table 502.3 shall comply with the building envelope provisions of ASHRAE/IESNA 90.1.

— [IECC 2009 §502.1.1](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/commercial-energy-efficiency.md)

## Fenestration: 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 | |
| Read the definition in the adopted IECC | Definitions | |
| Re-check the requirement that uses it | Residential Energy Efficiency (IECC 2009) | |
| Re-check the requirement that uses it | Energy Efficiency (IRC 2009) | |
| Re-check the requirement that uses it | Commercial Energy Efficiency (IECC 2009) | |
| Re-check the requirement that uses it | Definitions (IECC 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.

## Where can you explore related guidance?

- [Explore all glossary guidance](https://harth.build/resources/glossary.md)
- [Building: Building Code Definition](https://harth.build/resources/glossary/building.md)
- [Construction Documents: Building Code Definition](https://harth.build/resources/glossary/construction-documents.md)
- [Registered Design Professional: Building Code Definition](https://harth.build/resources/glossary/registered-design-professional.md)
- [Dwelling Unit: Building Code Definition](https://harth.build/resources/glossary/dwelling-unit.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 fenestration?

The International Residential Code (IRC) 2009 defines it in Definitions as: “Skylights, roof windows, vertical windows (whether fixed or moveable); opaque doors; glazed doors; glass block; and combination opaque/glazed doors.” 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 fenestration the same way?

No. IRC 2009, IECC 2009 all define the term, but the wording is not identical, and a difference in wording can change which requirements are triggered. The comparison table above sets the versions side by side so you can read the one that governs your question.

### Which parts of the code depend on fenestration?

In this corpus the term is used across 11 chapters, led by Residential Energy Efficiency in the IECC 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 correct definition for fenestration?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “Skylights, roof windows, vertical windows (whether fixed or moveable); opaque doors; glazed doors; glass block; and combination opaque/glazed doors.” It is defined in IRC 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.

### What is fenestration in a building?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “Skylights, roof windows, vertical windows (whether fixed or moveable); opaque doors; glazed doors; glass block; and combination opaque/glazed doors.” It is defined in IRC 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.

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