# Modified Bitumen Roof Covering: Building Code Definition > How the IBC 2009, IRC 2009 define modified bitumen roof covering, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/modified-bitumen-roof-covering/ - 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, IRC 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 | 4 (counted across the codes hosted here) | | Wording identical across codes | Yes (compare before citing one code's wording under another) | ## Direct answer Modified bitumen roof covering is a defined term in the International Building Code (IBC) 2009, in Roof Assemblies and Rooftop Structures. The code's own words are: “One or more layers of polymer-modified asphalt sheets. The sheet materials shall be fully adhered or mechanically attached to the substrate or held in place with an approved ballast layer.” The IRC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 4 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. *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? **Modified Bitumen Roof Covering** — IBC 2009, Roof Assemblies and Rooftop Structures: > One or more layers of polymer-modified asphalt sheets. The sheet materials shall be fully adhered or mechanically attached to the substrate or held in place with an approved ballast layer. ![Labeled code-term definition diagram: Modified Bitumen Roof Covering: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/modified-bitumen-roof-covering/diagram-1344.webp) *How the IBC 2009, IRC 2009 define modified bitumen roof covering, 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 **Modified Bitumen Roof Covering**, in identical words. | Code | Where it is defined | Definition | | --- | --- | --- | | IBC 2009 | [Roof Assemblies and Rooftop Structures](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/roof-assemblies-and-rooftop-structures.md) | One or more layers of polymer-modified asphalt sheets. The sheet materials shall be fully adhered or mechanically attached to the substrate or held in place with an approved ballast layer. | | IRC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | One or more layers of polymer modified asphalt sheets. The sheet materials shall be fully adhered or mechanically attached to the substrate or held in place with an approved ballast layer. | ## Where modified bitumen roof covering is used in the code The term appears in 4 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 | 3 | | [Roof Assemblies](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/roof-assemblies.md) | IRC 2009 | 2 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 1 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 | ## The terms modified bitumen roof covering is built out of The definition above leans on 3 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what modified bitumen roof covering covers: - **[Approved](https://harth.build/resources/glossary/approved.md)** — IBC 2009: Acceptable to the code official or authority having jurisdiction. - **[Ballast](https://harth.build/resources/glossary/ballast.md)** — IBC 2009: In roofing, ballast comes in the form of large stones or paver systems or light-weight interlocking paver systems and is used to provide uplift resistance for roofing systems that are not adhered or mechanically attached to the roof deck. - **[Shall](https://harth.build/resources/glossary/shall.md)** — IRC 2009: The term, when used in the code, is construed as mandatory. ## Modified Bitumen Roof Covering: 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 | | | Read the definition in the adopted IRC | Definitions | | | 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) | | | Re-check the requirement that uses it | Definitions (IRC 2009) | | | Confirm the dependent definition | Approved | | | Confirm the dependent definition | Ballast | | | Confirm the dependent definition | Shall | | | 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) - [Approved: Building Code Definition](https://harth.build/resources/glossary/approved.md) - [Ballast: Building Code Definition](https://harth.build/resources/glossary/ballast.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 modified bitumen roof covering? The International Building Code (IBC) 2009 defines it in Roof Assemblies and Rooftop Structures as: “One or more layers of polymer-modified asphalt sheets. The sheet materials shall be fully adhered or mechanically attached to the substrate or held in place with an approved ballast layer.” 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 modified bitumen roof covering? In this corpus the term is used across 4 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. ### What is modified bitumen roof covering? In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Roof Assemblies and Rooftop Structures: “One or more layers of polymer-modified asphalt sheets. The sheet materials shall be fully adhered or mechanically attached to the substrate or held in place with an approved ballast layer.” It is defined in IBC 2009, IRC 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. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fmodified-bitumen-roof-covering%2F - View this page in a browser: https://harth.build/resources/glossary/modified-bitumen-roof-covering/ - All resources for agents: https://harth.build/llms.txt