# Water-resistive Barrier: Building Code Definition

> How the IBC 2009, IRC 2009 define water-resistive barrier, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/water-resistive-barrier/
- 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 Exterior Walls (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 6 (counted across the codes hosted here) |
| Wording identical across codes | Yes (compare before citing one code's wording under another) |

## Direct answer

Water-resistive barrier is a defined term in the International Building Code (IBC) 2009, in Exterior Walls. The code's own words are: “A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly.” The IRC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 6 chapters of this corpus, most often in Wall Covering (IRC 2009), Exterior Walls (IBC 2009), Gypsum Board and Plaster (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?

**Water-resistive Barrier** — IBC 2009, Exterior Walls:

> A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly.

![Labeled code-term definition diagram: Water-resistive Barrier: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/water-resistive-barrier/diagram-1344.webp)

*How the IBC 2009, IRC 2009 define water-resistive barrier, 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 **Water-resistive Barrier**, in identical words.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IBC 2009 | [Exterior Walls](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/exterior-walls.md) | A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly. |
| IRC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly. |

## Where water-resistive barrier 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 |
| --- | --- | --- |
| [Wall Covering](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-covering.md) | IRC 2009 | 37 |
| [Exterior Walls](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/exterior-walls.md) | IBC 2009 | 15 |
| [Gypsum Board and Plaster](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/gypsum-board-and-plaster.md) | IBC 2009 | 13 |
| [Structural Tests and Special Inspections](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-tests-and-special-inspections.md) | IBC 2009 | 8 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 2 |
| [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 water-resistive barrier, quoted from the 2009 text hosted here:

> 15 asphalt felt, free from holes and breaks, complying with ASTM D 226 for Type 1 felt or other approved water-resistive barrier shall be applied over studs or sheathing ofall exterior walls.

— [IRC 2009 §R703.2](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-covering.md)

> The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1404.2, and a means for draining water that enters the assembly to the exterior.

— [IBC 2009 §1403.2](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/exterior-walls.md)

> A water-resistive barrier shall be provided in accordance with Section 2510.6.

— [IBC 2009 §2510.5.2.2](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/gypsum-board-and-plaster.md)


## The terms water-resistive barrier 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 water-resistive barrier covers:

- **[Exterior Wall Covering](https://harth.build/resources/glossary/exterior-wall-covering.md)** — IBC 2009: A material or assembly of materials applied on the exterior side of exterior walls for the purpose of providing a weather-resisting barrier, insulation or for aesthetics, including but not limited to, veneers, siding, exterior insulation and finish systems, architectural trim …
- **[Exterior Wall](https://harth.build/resources/glossary/exterior-wall.md)** — IBC 2009: A wall, bearing or nonbearing, that is used as an enclosing wall for a building, other than a fire wall, and that has a slope of 60 degrees (1.05 rad) or greater with the horizontal plane.
- **[Liquid](https://harth.build/resources/glossary/liquid.md)** — IBC 2009: A material that has a melting point that is equal to or less than 68°F (20°C) and a boiling point that is greater than 68°F (20°C) at 14.7 pounds per square inch absolute (psia) (101 kPa).

## Water-resistive Barrier: 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 | Exterior Walls | |
| Read the definition in the adopted IRC | Definitions | |
| Re-check the requirement that uses it | Wall Covering (IRC 2009) | |
| Re-check the requirement that uses it | Exterior Walls (IBC 2009) | |
| Re-check the requirement that uses it | Gypsum Board and Plaster (IBC 2009) | |
| Re-check the requirement that uses it | Structural Tests and Special Inspections (IBC 2009) | |
| Confirm the dependent definition | Exterior Wall Covering | |
| Confirm the dependent definition | Exterior Wall | |
| Confirm the dependent definition | Liquid | |
| 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)
- [Exterior Wall Covering: Building Code Definition](https://harth.build/resources/glossary/exterior-wall-covering.md)
- [Exterior Wall: Building Code Definition](https://harth.build/resources/glossary/exterior-wall.md)
- [Liquid: Building Code Definition](https://harth.build/resources/glossary/liquid.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 water-resistive barrier?

The International Building Code (IBC) 2009 defines it in Exterior Walls as: “A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly.” 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 water-resistive barrier?

In this corpus the term is used across 6 chapters, led by Wall Covering 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.

### What is a water-resistive barrier?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Exterior Walls: “A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly.” 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.

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