# Solar Heat Gain Coefficient (SHGC): Building Code Definition > How the IRC 2009, IECC 2009 define solar heat gain coefficient (shgc), where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/solar-heat-gain-coefficient-shgc/ - 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 | 6 (counted across the codes hosted here) | | Wording identical across codes | No (compare before citing one code's wording under another) | ## Direct answer Solar heat gain coefficient (shgc) is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The solar heat gain through a fenestration or glazing assembly relative to the incident solar radiation (Btu/h· ft2 • OF).” 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 6 chapters of this corpus, most often in Energy Efficiency (IRC 2009), Commercial Energy Efficiency (IECC 2009), Climate Zones (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? **Solar Heat Gain Coefficient (SHGC)** — IRC 2009, Definitions: > The solar heat gain through a fenestration or glazing assembly relative to the incident solar radiation (Btu/h· ft2 • OF). ![Labeled code-term definition diagram: Solar Heat Gain Coefficient (SHGC): Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/solar-heat-gain-coefficient-shgc/diagram-1344.webp) *How the IRC 2009, IECC 2009 define solar heat gain coefficient (shgc), 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 **Solar Heat Gain Coefficient (SHGC)**, 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) | The solar heat gain through a fenestration or glazing assembly relative to the incident solar radiation (Btu/h· ft2 • OF). | | IECC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) | The ratio of the solar heat gain entering the space through the fenestration assembly to the incident solar radiation. Solar heat gain includes directly transmitted solar heat and absorbed solar radiation which is then reradiated, conducted or convected into the space. | ## Where solar heat gain coefficient (shgc) 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 | | --- | --- | --- | | [Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/energy-efficiency.md) | IRC 2009 | 6 | | [Commercial Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/commercial-energy-efficiency.md) | IECC 2009 | 4 | | [Climate Zones](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/climate-zones.md) | IECC 2009 | 2 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) | IECC 2009 | 1 | | [Residential Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/residential-energy-efficiency.md) | IECC 2009 | 1 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 | ## The terms solar heat gain coefficient (shgc) 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 solar heat gain coefficient (shgc) covers: - **[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. - **[Btu/h](https://harth.build/resources/glossary/btu-h.md)** — IRC 2009: The listed maximum capacity of an appliance, absorption unit or burner expressed in British thermal units input per hour. ## Solar Heat Gain Coefficient (SHGC): 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 | Energy Efficiency (IRC 2009) | | | Re-check the requirement that uses it | Commercial Energy Efficiency (IECC 2009) | | | Re-check the requirement that uses it | Climate Zones (IECC 2009) | | | Re-check the requirement that uses it | Definitions (IECC 2009) | | | Confirm the dependent definition | Fenestration | | | Confirm the dependent definition | Btu/h | | | 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) - [Fenestration: Building Code Definition](https://harth.build/resources/glossary/fenestration.md) - [Btu/h: Building Code Definition](https://harth.build/resources/glossary/btu-h.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 solar heat gain coefficient (shgc)? The International Residential Code (IRC) 2009 defines it in Definitions as: “The solar heat gain through a fenestration or glazing assembly relative to the incident solar radiation (Btu/h· ft2 • OF).” 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 solar heat gain coefficient (shgc) 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 solar heat gain coefficient (shgc)? In this corpus the term is used across 6 chapters, led by Energy Efficiency in the IRC 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. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fsolar-heat-gain-coefficient-shgc%2F - View this page in a browser: https://harth.build/resources/glossary/solar-heat-gain-coefficient-shgc/ - All resources for agents: https://harth.build/llms.txt