Updated 2026-09-07

Building Code Glossary

Base Flood: Building Code Definition

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

On this page

Last updated September 7, 2026 · 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.

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Direct answer

Base flood is a defined term in the International Building Code (IBC) 2009, in Structural Design. The code's own words are: “The flood having a I-percent chance of being equaled or exceeded in any given year.” 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 4 chapters of this corpus, most often in Building Planning (IRC 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, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.

What does this term mean?

Base Flood — IBC 2009, Structural Design:

The flood having a I-percent chance of being equaled or exceeded in any given year.

Labeled code-term definition diagram: Base Flood: Building Code Definition — How the IBC 2009 define base flood, where the wording differs, and which chapters depend on the term.

What must be verified before using this guidance?

Base Flood is defined once in this corpus, in the Structural Design chapter of the International Building Code (IBC) 2009:

The flood having a I-percent chance of being equaled or exceeded in any given year.

Where base flood 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
Building Planning	IRC 2009	9
Structural Design	IBC 2009	5
Definitions	IBC 2009	2
Definitions	IPC 2009	1

The term in use

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

Located at the base flood elevation plus 1 foot (305 mm), or the design flood elevation, whichever is higher, if the lowest horizontal structural member is oriented perpendicular to the direction of wave approach, where perpendicular shall mean greater than 20 degrees (0.35 rad) from the direction of approach.

— IRC 2009, Building Planning

Base Flood: what to open, and in what order

Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.

Check	Where	Confirmed
Read the definition in the adopted IBC	Structural Design
Re-check the requirement that uses it	Building Planning (IRC 2009)
Re-check the requirement that uses it	Structural Design (IBC 2009)
Re-check the requirement that uses it	Definitions (IBC 2009)
Re-check the requirement that uses it	Definitions (IPC 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.

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 publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.

Source links

Frequently asked questions

What is the code definition of base flood?

The International Building Code (IBC) 2009 defines it in Structural Design as: “The flood having a I-percent chance of being equaled or exceeded in any given year.” 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 base flood?

In this corpus the term is used across 4 chapters, led by Building Planning 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 considered a base flood?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Structural Design: “The flood having a I-percent chance of being equaled or exceeded in any given year.” 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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