Your job is governed by whichever model codes your city or county has formally adopted, plus their local amendments, at the edition they adopted. As a rough map: the IRC covers houses, the IBC covers everything else, the NEC covers electrical, the IPC or UPC covers plumbing, the IMC covers mechanical, and the IECC covers energy. The catch is that none of those books mean anything until your jurisdiction adopts them into law, and they can change what they adopt. So knowing the family of codes is step one, but the number that actually gets enforced comes from your Authority Having Jurisdiction (AHJ), not from the model book on the shelf.
The model codes are not law until your jurisdiction adopts them
The codes most trades work under are model codes. A private body writes them, publishes a new edition every three years, and then states and local jurisdictions choose whether and when to adopt each one, often with their own changes bolted on.
Two things follow from that, and they are the whole reason this matters:
- A model code has no legal force on its own. It only binds you once your jurisdiction adopts it. Until then it is a recommendation.
- Your jurisdiction is usually behind the newest edition, and it amends. Adoption lags publication by anywhere from one year to many, and local amendments layer on top. The town next door can be on a different edition with different changes.
So "what does the code say" is really two questions: which edition did my AHJ adopt, and what did they amend. Get that from the Permit and Code Lookup tool and confirm it with your building department before you rely on any number.
The building codes: IRC vs IBC
The two big building codes split by what you are building, not by trade:
- IRC, the International Residential Code. One- and two-family homes and townhouses up to three stories, as your AHJ adopts it. The IRC is the all-in-one book for houses: it wraps building, plumbing, mechanical, and energy into a single volume so a homebuilder is not flipping through five codes.
- IBC, the International Building Code. Everything else. Apartments of three or more units, commercial, retail, schools, churches, offices, high-rises. Once a townhouse goes over three stories, or a project hits three or more dwelling units, it flips out of the IRC and into IBC territory.
The one-sentence version: the IRC is your house, the IBC is everything bigger. That boundary is how the codes themselves define their scope, but your jurisdiction adopts and can tweak it, so confirm which book applies if your project sits near the line.
The trade codes: electrical, plumbing, mechanical
Underneath the building code sit the systems codes, and these are the ones most specialty trades live in:
- NEC, the National Electrical Code (NFPA 70). Electrical in essentially every occupancy. It is published by the NFPA, not the same body as the I-Codes, but every state enforces some edition of it. Note the NEC runs on its own three-year cycle, and a jurisdiction can be on a different NEC edition than its building-code edition.
- IPC or UPC, plumbing. There are two competing model plumbing codes. The IPC (International Plumbing Code) is more common across the East and Midwest; the UPC (Uniform Plumbing Code, published by IAPMO) is more common across the West and Southwest. Which one covers you is a regional split, and some big cities inside an IPC state use the UPC locally, so never assume, confirm.
- IMC, the International Mechanical Code. HVAC, ventilation, and exhaust, widely adopted.
For a house under the IRC, remember the plumbing, mechanical, and energy provisions are bundled inside the IRC itself, though many jurisdictions still cross-reference the standalone codes.
The energy code: IECC
The IECC, the International Energy Conservation Code, governs the building envelope and energy use, insulation, air sealing, windows, and equipment efficiency, for both houses and larger buildings. It moves faster than the building codes in many places, and a jurisdiction can be on a newer IECC than its IRC. The IECC gives you more than one way to comply, a prescriptive path with tables and performance paths where you model the whole building, which is worth knowing before you assume you have to hit a specific insulation value.
The two-city warning: NYC and Chicago
A couple of major jurisdictions do not adopt the model codes wholesale and run their own code regimes. New York City and Chicago both maintain heavily amended local codes, including their own electrical and plumbing codes, that override the state defaults. If you work in one of those, the model-code map above is only a starting point. The local code controls, so get it from the city directly.
The move
Do not memorize a number from a code book and carry it job to job, because the edition and the amendments change with the jurisdiction. Instead, for each job, pin down four things: which building code applies (IRC or IBC), which trade codes apply to your scope (NEC, IPC or UPC, IMC), which edition your AHJ adopted, and what they amended. The Permit and Code Lookup tool and Working in Your State point you to your jurisdiction's adopted codes; the building department confirms the amendments.
Common questions
Is the NEC a national law I have to follow everywhere?
No. The NEC is a model code published by the NFPA, and it only has legal force where a state or local jurisdiction adopts it, which they all do but not all on the same edition. So there is no single national electrical rule in force everywhere at once. Different states enforce different NEC editions, and a few big cities amend it heavily. Confirm which NEC edition your jurisdiction adopted before you wire to a number you remember from another job.
What is the difference between the IRC and the IBC?
The IRC covers one- and two-family homes and townhouses up to three stories; the IBC covers everything else, including apartments of three or more units and all commercial buildings. The line is the type and size of building, not your trade. A project flips from IRC to IBC once it passes three stories as a townhouse or hits three or more dwelling units. If your job sits near that boundary, confirm which code applies with your building department, because it changes the rules you build to.
Do I follow the newest edition of the code?
Not automatically. You follow whatever edition your jurisdiction has formally adopted, which is usually older than the newest published edition. Model codes come out every three years, but adoption lags by anywhere from a year to many, and jurisdictions add local amendments. Building to the newest book when your AHJ is on an older one can still fail inspection. Confirm the adopted edition and amendments with the Permit and Code Lookup tool.
Which plumbing code applies, the IPC or the UPC?
It depends on your location. The IPC is more common across the East and Midwest, the UPC across the West and Southwest, but the only way to be sure is to confirm with your AHJ. Some large cities inside an IPC state use the UPC locally, and a handful of states run their own state plumbing code entirely. The two codes differ in real ways, so build to the one your jurisdiction actually adopted, not the one common in the next state over.
The honest bit
- Which model code governs which kind of work is stable, and that is what this guide gives you. Which edition your jurisdiction adopted, and what they changed by amendment, is not stable and is not national. Get it from the Permit and Code Lookup tool and confirm with your building department.
- Every enforceable number, spans, depths, clearances, insulation values, deliberately does not appear here, because it depends on your adopted edition and local amendments and some provisions were renumbered between editions. Route those to the Permit and Code Lookup tool and your AHJ.
- This is general guidance, not code interpretation. The AHJ's reading of the adopted code is the one that counts on your job.
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