IBC vs. IRC: Which Building Code Applies? (2026)
IBC vs. IRC — which International Code applies to your project by occupancy and scale, and why local adoption always governs.
IBC vs. IRC: Which Building Code Applies? (2026)
Direct answer
The International Residential Code (IRC) is a standalone code for detached one- and two-family dwellings and townhouses not more than three stories above grade. The International Building Code (IBC) governs all other occupancies — commercial, assembly, larger multifamily, and so on. A small house typically falls under the IRC; almost everything else falls under the IBC. Always confirm which editions your Authority Having Jurisdiction (AHJ) has adopted, since adoption and amendments vary by jurisdiction.
Key facts
| Metric | Value | Notes |
|---|---|---|
| IRC | 1- & 2-family dwellings, townhouses ≤3 stories | standalone residential code |
| IBC | All other occupancies | commercial, larger multifamily, etc. |
| Deciding factors | Occupancy & scale | |
| Governing authority | Locally adopted edition + amendments | confirm with AHJ |
Side by side
| Dimension | IRC | IBC |
|---|---|---|
| Scope | 1- & 2-family dwellings, townhouses ≤3 stories | All other occupancies |
| Typical projects | Houses, duplexes, small townhouses | Commercial, assembly, larger multifamily |
| Publisher | ICC | ICC |
| What governs locally | AHJ-adopted edition + amendments | AHJ-adopted edition + amendments |
How to decide
Start with occupancy and scale. A detached house or duplex — and townhouses within the IRC's limits — generally use the IRC. Commercial, assembly, institutional, and larger residential buildings use the IBC. Then confirm the AHJ's adopted edition, because local amendments can shift the details.
The rule that overrides all others
What's published is not necessarily what's law where you build. The adopting jurisdiction decides the edition and amendments — verify against the AHJ-adopted code before relying on any scope statement here.
Frequently asked questions
Does a townhouse fall under the IRC or IBC?
Townhouses not more than three stories above grade with separate means of egress can fall under the IRC, but larger or differently configured multifamily buildings fall under the IBC. Because definitions and thresholds can be locally amended, confirm the classification with your AHJ for the specific project.
Which code applies to an apartment building?
Most apartment buildings are Group R occupancies under the IBC rather than the IRC, since the IRC is limited to one- and two-family dwellings and qualifying townhouses. Verify the occupancy classification and adopted edition with your jurisdiction.
Are the IBC and IRC used everywhere in the US?
They are model codes published by the ICC and adopted — often with amendments — by states and local jurisdictions. What legally applies is the edition your jurisdiction has adopted, which may lag the newest publication or modify it. Always check the AHJ.
Related
Source & method: General scope descriptions of the ICC's International Building Code and International Residential Code. Scope, editions, and amendments are set by the adopting jurisdiction — verify against the AHJ-adopted edition for your project.