# Single-ply Membrane: Building Code Definition > How the IBC 2009 define single-ply membrane, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/single-ply-membrane/ - 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 Roof Assemblies and Rooftop Structures (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 Single-ply membrane is a defined term in the International Building Code (IBC) 2009, in Roof Assemblies and Rooftop Structures. The code's own words are: “A roofing membrane that is field applied using one layer of membrane material (either homogeneous or composite) rather than multiple layers.” 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 Roof Assemblies and Rooftop Structures (IBC 2009), Roof Assemblies (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? **Single-ply Membrane** — IBC 2009, Roof Assemblies and Rooftop Structures: > A roofing membrane that is field applied using one layer of membrane material (either homogeneous or composite) rather than multiple layers. ![Labeled code-term definition diagram: Single-ply Membrane: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/single-ply-membrane/diagram-1344.webp) *How the IBC 2009 define single-ply membrane, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Single-ply Membrane** is defined once in this corpus, in the [Roof Assemblies and Rooftop Structures](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/roof-assemblies-and-rooftop-structures.md) chapter of the International Building Code (IBC) 2009: > A roofing membrane that is field applied using one layer of membrane material (either homogeneous or composite) rather than multiple layers. ## Where single-ply membrane 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 | | --- | --- | --- | | [Roof Assemblies and Rooftop Structures](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/roof-assemblies-and-rooftop-structures.md) | IBC 2009 | 5 | | [Roof Assemblies](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/roof-assemblies.md) | IRC 2009 | 4 | | [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 single-ply membrane, quoted from the 2009 text hosted here: > Thermoset single-ply membrane roofs shall have a design slope of a minimum of one-fourth unit vertical in 12 units horizontal (2-percent slope) for drainage. — [IBC 2009 §1507.12.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/roof-assemblies-and-rooftop-structures.md) > Thermoplastic single-ply membrane roofs shall have a design slope of a minimum of one-fourth unit vertical in 12 units horizontal (2-percent slope). — [IRC 2009 §R905.13.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/roof-assemblies.md) ## Single-ply Membrane: 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 | Roof Assemblies and Rooftop Structures | | | Re-check the requirement that uses it | Roof Assemblies and Rooftop Structures (IBC 2009) | | | Re-check the requirement that uses it | Roof Assemblies (IRC 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) - [Aggregate: Building Code Definition](https://harth.build/resources/glossary/aggregate.md) - [Roof Assembly: Building Code Definition](https://harth.build/resources/glossary/roof-assembly.md) - [Roof Deck: Building Code Definition](https://harth.build/resources/glossary/roof-deck.md) - [Roof Covering: Building Code Definition](https://harth.build/resources/glossary/roof-covering.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 single-ply membrane? The International Building Code (IBC) 2009 defines it in Roof Assemblies and Rooftop Structures as: “A roofing membrane that is field applied using one layer of membrane material (either homogeneous or composite) rather than multiple layers.” 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 single-ply membrane? In this corpus the term is used across 3 chapters, led by Roof Assemblies and Rooftop Structures 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. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fsingle-ply-membrane%2F - View this page in a browser: https://harth.build/resources/glossary/single-ply-membrane/ - All resources for agents: https://harth.build/llms.txt