# Shell: Building Code Definition

> How the IBC 2009 define shell, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/shell/
- 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 | 14 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Shell is a defined term in the International Building Code (IBC) 2009, in Masonry. The code's own words are: “The outer portion of a hollow masonry unit as placed in masonry.” 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 14 chapters of this corpus, most often in Swimming Pools (IRC 2009), Explosives and Fireworks (IFC 2009), Flammable and Combustible Liquids (IFC 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?

**Shell** — IBC 2009, Masonry:

> The outer portion of a hollow masonry unit as placed in masonry.

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

*How the IBC 2009 define shell, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Shell** 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:

> The outer portion of a hollow masonry unit as placed in masonry.

## Where shell is used in the code

The term appears in 14 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Swimming Pools](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/swimming-pools.md) | IRC 2009 | 52 |
| [Explosives and Fireworks](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/explosives-and-fireworks.md) | IFC 2009 | 43 |
| [Flammable and Combustible Liquids](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/flammable-and-combustible-liquids.md) | IFC 2009 | 33 |
| [Wall Construction](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/wall-construction.md) | IRC 2009 | 8 |
| [Devices and Luminaires](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/devices-and-luminaires.md) | IRC 2009 | 7 |
| [Concrete](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md) | IBC 2009 | 5 |
| [Flammable Gases and Flammable Cryogenic Fluids](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/flammable-gases-and-flammable-cryogenic-fluids.md) | IFC 2009 | 4 |
| [Use and Occupancy Classification](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/use-and-occupancy-classification.md) | IBC 2009 | 2 |
| [Cryogenic Fluids](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/cryogenic-fluids.md) | IFC 2009 | 2 |
| [Boilers, Water Heaters and Pressure Vessels](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/boilers-water-heaters-and-pressure-vessels.md) | IMC 2009 | 2 |
| [Water Heaters](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-heaters.md) | IPC 2009 | 2 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 1 |

_2 further chapters mention the term._

### The term in use

How the code actually writes about shell, quoted from the 2009 text hosted here:

> Where a nonmetallic conduit is installed between a forming shell and a junction box, transformer enclosure, or other enclosure, a 8 AWG insulated copper bonding jumper shall be installed in this conduit except where a listed low-voltage lighting system not requiring grounding is used.

— [IRC 2009 §E4205.3](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/swimming-pools.md)

> A plan establishing procedures to follow and actions to be taken in the event that a shell fails to ignite in, or discharge from, a mortar or fails to function over the fallout area or other malfunctions shall be provided to the fire code ofl1cial.

— [IFC 2009 §3308.2](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/explosives-and-fireworks.md)

> Above-ground tanks with connections located below normal liquid level shall be provided with internal or external isolation valves located as close as practical to the shell of the tank.

— [IFC 2009 §3403.6.7](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/flammable-and-combustible-liquids.md)


## Shell compared with Web

These two are the closest pair in the 2009 I-Codes: about 64 per cent of their defining words are the same. The code states both and compares neither, so the difference is worth naming.

| | Wording unique to it |
| --- | --- |
| **Shell** (IBC 2009) | outer |
| [Web](https://harth.build/resources/glossary/web.md) (IBC 2009) | interior, solid |

Everything else in the two definitions is shared. If a project turns on which of the two applies, those words are the whole of the test — and a local amendment that edits one of them without editing the other moves the boundary between shell and web.

## The terms shell 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 shell covers:

- **[Masonry Unit](https://harth.build/resources/glossary/masonry-unit.md)** — IBC 2009: Brick, tile, stone, glass block or concrete block conforming to the requirements specified in Section 2103.
- **[Masonry](https://harth.build/resources/glossary/masonry.md)** — IBC 2009: A built-up construction or combination of building units or materials of clay, shale, concrete, glass, gypsum, stone or other approved units bonded together with or without mortar or grout or other accepted methods of joining.

## Shell: 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 | Swimming Pools (IRC 2009) | |
| Re-check the requirement that uses it | Explosives and Fireworks (IFC 2009) | |
| Re-check the requirement that uses it | Flammable and Combustible Liquids (IFC 2009) | |
| Re-check the requirement that uses it | Wall Construction (IRC 2009) | |
| Confirm the dependent definition | Masonry Unit | |
| Confirm the dependent definition | Masonry | |
| 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)
- [Masonry Unit: Building Code Definition](https://harth.build/resources/glossary/masonry-unit.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 shell?

The International Building Code (IBC) 2009 defines it in Masonry as: “The outer portion of a hollow masonry unit as placed in masonry.” 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 shell?

In this corpus the term is used across 14 chapters, led by Swimming Pools 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 the definition of a building shell?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Masonry: “The outer portion of a hollow masonry unit as placed in masonry.” It is defined in IBC 2009. It is not the same as Building, which the IBC 2009 defines separately as “Any structure used or intended for supporting or sheltering any use or occupancy.” 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.

### What is shell vs terminal?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Masonry: “The outer portion of a hollow masonry unit as placed in masonry.” It is defined in IBC 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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