# Autoclaved Aerated Concrete (AAC): Building Code Definition > How the IBC 2009 define autoclaved aerated concrete (aac), where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/autoclaved-aerated-concrete-aac/ - 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 Masonry (model text, not a jurisdiction's adopted text) | | Chapters using the term | 3 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Autoclaved aerated concrete (aac) is a defined term in the International Building Code (IBC) 2009, in Masonry. The code's own words are: “Low-density cementitious product of calcium silicate hydrates, whose material specifications are defined in ASTM C 1386.” 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 3 chapters of this corpus, most often in Masonry (IBC 2009), Structural Design (IBC 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? **Autoclaved Aerated Concrete (AAC)** — IBC 2009, Masonry: > Low-density cementitious product of calcium silicate hydrates, whose material specifications are defined in ASTM C 1386. ![Labeled code-term definition diagram: Autoclaved Aerated Concrete (AAC): Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/autoclaved-aerated-concrete-aac/diagram-1344.webp) *How the IBC 2009 define autoclaved aerated concrete (aac), where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Autoclaved Aerated Concrete (AAC)** is defined once in this corpus, in the [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) chapter of the International Building Code (IBC) 2009: > Low-density cementitious product of calcium silicate hydrates, whose material specifications are defined in ASTM C 1386. ## Where autoclaved aerated concrete (aac) is used in the code The term appears in 3 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next. | Chapter | Code | Mentions | | --- | --- | --- | | [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) | IBC 2009 | 4 | | [Structural Design](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md) | IBC 2009 | 2 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 1 | ## Autoclaved Aerated Concrete (AAC): 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 | Masonry | | | Re-check the requirement that uses it | Masonry (IBC 2009) | | | Re-check the requirement that uses it | Structural Design (IBC 2009) | | | Re-check the requirement that uses it | Definitions (IBC 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) - [Chimney: Building Code Definition](https://harth.build/resources/glossary/chimney.md) - [Tile: Building Code Definition](https://harth.build/resources/glossary/tile.md) - [Fireplace: Building Code Definition](https://harth.build/resources/glossary/fireplace.md) - [Masonry: Building Code Definition](https://harth.build/resources/glossary/masonry.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 autoclaved aerated concrete (aac)? The International Building Code (IBC) 2009 defines it in Masonry as: “Low-density cementitious product of calcium silicate hydrates, whose material specifications are defined in ASTM C 1386.” 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 autoclaved aerated concrete (aac)? In this corpus the term is used across 3 chapters, led by Masonry 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 is AAC masonry? AAC Masonry is a separate defined term. The IBC 2009 defines it as: “Masonry made of autoclaved aerated concrete (AAC) units, manufactured without internal reinforcement and bonded together using thin- or thick-bed mortar.” That is not the same as autoclaved aerated concrete (aac), which the IBC 2009 defines as “Low-density cementitious product of calcium silicate hydrates, whose material specifications are defined in ASTM C 1386.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fautoclaved-aerated-concrete-aac%2F - View this page in a browser: https://harth.build/resources/glossary/autoclaved-aerated-concrete-aac/ - All resources for agents: https://harth.build/llms.txt