# Skylight, Unit: Building Code Definition > How the IBC 2009 define skylight, unit, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/skylight-unit/ - 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 | IBC 2009 (2009 editions transcribed in this corpus) | | Primary source | IBC 2009 Definitions (model text, not a jurisdiction's adopted text) | | Chapters using the term | 6 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Skylight, unit is a defined term in the International Building Code (IBC) 2009, in Definitions. The code's own words are: “A factory-assembled, glazed fenestration unit, containing one panel of glazing material that allows for natural lighting through an opening in the roof assembly while preserving the weather-resistant barrier of the roof.” No other I-Code in this corpus defines it, so the IBC 2009 definition is the one to work from. The term is used in 6 chapters of this corpus, most often in Glass and Glazing (IBC 2009), Building Planning (IRC 2009), Definitions (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](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? **Skylight, Unit** — IBC 2009, Definitions: > A factory-assembled, glazed fenestration unit, containing one panel of glazing material that allows for natural lighting through an opening in the roof assembly while preserving the weather-resistant barrier of the roof. ![Labeled code-term definition diagram: Skylight, Unit: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/skylight-unit/diagram-1344.webp) *How the IBC 2009 define skylight, unit, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Skylight, Unit** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) chapter of the International Building Code (IBC) 2009: > A factory-assembled, glazed fenestration unit, containing one panel of glazing material that allows for natural lighting through an opening in the roof assembly while preserving the weather-resistant barrier of the roof. ## Where skylight, unit is used in the code The term appears in 6 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next. | Chapter | Code | Mentions | | --- | --- | --- | | [Glass and Glazing](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/glass-and-glazing.md) | IBC 2009 | 14 | | [Building Planning](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md) | IRC 2009 | 8 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 2 | | [Plastic](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/plastic.md) | IBC 2009 | 2 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) | IECC 2009 | 1 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 | ## Skylight, Unit compared with Unit Skylight These two are the closest pair in the 2009 I-Codes: about 93 per cent of their defining words are the same. The code states both and compares neither, so the difference is worth naming. | | Wording unique to it | | --- | --- | | **Skylight, Unit** (IBC 2009) | lighting | | [Unit Skylight](https://harth.build/resources/glossary/unit-skylight.md) (IRC 2009) | daylighting | Everything else in the two definitions is shared. If a project turns on which of the two applies, those words are the whole of the test — and a local amendment that edits one of them without editing the other moves the boundary between skylight, unit and unit skylight. ## The terms skylight, unit is built out of The definition above leans on 2 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what skylight, unit covers: - **[Roof Assembly](https://harth.build/resources/glossary/roof-assembly.md)** — IBC 2009: A system designed to provide weather protection and resistance to design loads. - **[Fenestration](https://harth.build/resources/glossary/fenestration.md)** — IRC 2009: Skylights, roof windows, vertical windows (whether fixed or moveable); opaque doors; glazed doors; glass block; and combination opaque/glazed doors. ## Skylight, Unit: 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 IBC | Definitions | | | Re-check the requirement that uses it | Glass and Glazing (IBC 2009) | | | Re-check the requirement that uses it | Building Planning (IRC 2009) | | | Re-check the requirement that uses it | Definitions (IBC 2009) | | | Re-check the requirement that uses it | Plastic (IBC 2009) | | | Confirm the dependent definition | Roof Assembly | | | Confirm the dependent definition | Fenestration | | | 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) - [Roof Assembly: Building Code Definition](https://harth.build/resources/glossary/roof-assembly.md) - [Fenestration: Building Code Definition](https://harth.build/resources/glossary/fenestration.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 skylight, unit? The International Building Code (IBC) 2009 defines it in Definitions as: “A factory-assembled, glazed fenestration unit, containing one panel of glazing material that allows for natural lighting through an opening in the roof assembly while preserving the weather-resistant barrier of the roof.” 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 skylight, unit? In this corpus the term is used across 6 chapters, led by Glass and Glazing in the IBC 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 skylights in Florida? 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 skylight, unit, which the IBC 2009 defines as “A factory-assembled, glazed fenestration unit, containing one panel of glazing material that allows for natural lighting through an opening in the roof assembly while preserving the weather-resistant barrier of the roof.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted. ### What is a skylight in a building? In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Definitions: “A factory-assembled, glazed fenestration unit, containing one panel of glazing material that allows for natural lighting through an opening in the roof assembly while preserving the weather-resistant barrier of the roof.” It is defined in IBC 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. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fskylight-unit%2F - View this page in a browser: https://harth.build/resources/glossary/skylight-unit/ - All resources for agents: https://harth.build/llms.txt