What Plumbing Code Does My State Use?

Plumbing code adoption in the United States varies by state, county, city, and local building department. Some jurisdictions use the Uniform Plumbing Code (UPC), some use the International Plumbing Code (IPC), and others use a state-specific plumbing code based on one of those model codes.

The important point is that plumbing code is enforced locally. A state may adopt a model code, but cities and counties may also apply local amendments, different edition years, additional permit requirements, or stricter inspection rules. If you are comparing fixture unit results, it helps to review the UPC vs IPC plumbing code comparison before using a calculator.

Quick answer

To find the plumbing code for your project, check the building department for the city or county where the work will be permitted. The adopted code may be listed as the UPC, IPC, state plumbing code, residential code, building code, construction code, or local municipal plumbing ordinance.

The safest answer comes from the local authority having jurisdiction, not from a generic national list. Once you know the adopted code, use the DFU calculator and DFU chart with the correct assumptions.

Plumbing Code Types

When you search for your local plumbing code, you may see several different terms. The table below explains what those terms usually mean and why they matter for drain sizing, venting, materials, cleanouts, and inspections.

Code Type	What It Means	Why It Matters
UPC	Uniform Plumbing Code published by IAPMO	Often more prescriptive for drainage, venting, trap arms, wet venting, and fixture layout.
IPC	International Plumbing Code published by ICC	Often allows more design flexibility, especially for some venting and fixture grouping layouts.
State plumbing code	A state-adopted code based on UPC, IPC, or another model code	May include state-specific amendments, edition changes, and administrative rules.
Residential code	Plumbing provisions may appear inside a residential building code	Smaller residential projects may be reviewed under residential code provisions instead of a standalone plumbing code.
Local amendments	City or county modifications to the adopted base code	Can affect pipe sizing, venting, materials, cleanouts, water conservation, inspections, and permit documents.

Why State Plumbing Code Adoption Is Complicated

There is not one single national plumbing code that automatically applies to every building in the United States. Instead, plumbing codes are adopted by states and local jurisdictions. A model code only becomes enforceable when it is adopted into law by the authority having jurisdiction.

This means two homes in different cities may follow different plumbing requirements, even if they are in the same state. It also means an online plumbing calculator should clearly state which code assumptions it uses. For fixture unit totals, start with the DFU Calculator.

State Code vs Local Code

A state may adopt a plumbing code at the state level, but the local building department is usually where permits are submitted, plans are reviewed, inspections are scheduled, and code questions are resolved. For that reason, local verification is important even when you already know the state code.

State adoption tells you the base

The state code usually tells you the model code family, edition year, and statewide amendments.

Local adoption tells you the rules

The local building department may add amendments, permit submittal standards, inspection rules, or local interpretations.

For example, a city may require specific cleanout locations, approved materials, trench inspection steps, water conservation fixtures, or additional documentation beyond the base model code.

UPC States and Jurisdictions

The Uniform Plumbing Code is commonly used in many western states and local jurisdictions. Some states adopt a plumbing code based on the UPC and then modify it with state amendments. Other jurisdictions may adopt the UPC directly or use it as the basis for their own plumbing regulations.

UPC-based jurisdictions often pay close attention to trap arm length, venting layout, wet venting limits, cleanout access, pipe sizing, and drainage fixture unit tables. For design comparisons, see the UPC vs IPC plumbing code comparison.

IPC States and Jurisdictions

The International Plumbing Code is widely adopted across many states and municipalities. IPC-based jurisdictions may allow different fixture grouping, venting, and wet venting approaches than UPC-based jurisdictions.

This can affect how a bathroom group, kitchen, laundry room, building drain, or building sewer is designed. IPC-style assumptions may be more flexible in some layouts, but the adopted local edition and amendments still control the final answer.

How to Check Your Local Plumbing Code

The fastest way to avoid using the wrong code is to check the local building department before relying on a fixture-unit calculation or pipe sizing guide.

Search for your city or county building department website.
Look for a page called adopted codes, building codes, construction codes, code adoption, or permit requirements.
Find the adopted plumbing code and edition year.
Check whether local amendments modify the base code.
Confirm whether your project is reviewed under a plumbing code, residential code, or local ordinance.
Verify any project-specific questions before submitting plans or starting work.

What to write down

Code name, such as UPC, IPC, or state plumbing code
Edition year
Local amendments
Whether the project is residential or commercial
Whether the work needs plumbing, building, or combined permits
Name of the local authority having jurisdiction

What to Search For

Good search phrases include:

"[your city] adopted plumbing code"
"[your county] building department plumbing code"
"[your state] plumbing code adoption"
"[your city] local amendments plumbing code"
"[your jurisdiction] UPC IPC plumbing code"
"[your city] construction codes plumbing"
"[your county] residential plumbing code"

Example Code Lookup Workflow

Here is a simple workflow you can use when checking a real project location.

Search for the city or county building department, not just the state code.
Open the adopted codes or construction codes page and look for the plumbing section.
Note whether the page references UPC, IPC, a state plumbing code, or a residential code.
Look for local amendments, especially for materials, cleanouts, water conservation, and permit submittal requirements.
If the page is unclear, call or email the building department and ask which plumbing code and edition apply to your project address.

Why This Matters for DFU Calculations

Drainage fixture unit calculations are code-dependent. A toilet, shower, tub, lavatory, kitchen sink, dishwasher, clothes washer, urinal, or floor drain may be assigned different fixture unit values depending on the adopted code and edition.

Pipe sizing can also change depending on whether the pipe is horizontal or vertical, the slope of the pipe, the total fixture unit load, and the code table being used. After calculating fixture units, you may also want to compare common sizing guides such as 3-inch pipe DFU capacity and 4-inch sewer capacity.

Example: why the selected code changes the result

A private-use toilet, clothes washer, urinal, or public fixture may have different fixture-unit assumptions depending on whether you are using UPC or IPC values. If a remodel is close to a pipe sizing limit, those differences can affect whether a 2-inch, 3-inch, or 4-inch drain needs closer review.

Use the DFU Calculator to compare UPC and IPC fixture-unit assumptions, or check individual values in the DFU chart.

Building Drain vs Building Sewer Code Questions

Local code adoption can also affect how a pipe section is classified. A branch drain, building drain, building sewer, private lateral, and public sewer connection may have different sizing, cleanout, material, inspection, and connection requirements.

Before applying DFU totals to a pipe sizing table, identify whether you are reviewing a building drain or building sewer. The same pipe diameter may be reviewed differently depending on where it is located in the drainage system.

Local Amendments Can Override the Model Code

Even when a state adopts the UPC or IPC, the local jurisdiction may amend specific requirements. Amendments can affect approved materials, cleanout locations, venting rules, water conservation requirements, seismic provisions, freeze protection, inspection requirements, and permit documentation.

For this reason, the safest approach is to treat online information as a starting point and verify the adopted code with the authority having jurisdiction. This is especially important before cutting concrete, trenching a sewer line, relocating fixtures, adding an ADU, or submitting permit plans.

Common Plumbing Decisions Affected by Local Code

Plumbing code selection affects more than just the name of the code book. It can influence practical design decisions throughout a remodel, addition, ADU, or new build.

DFU totals

Fixture-unit values can differ between UPC, IPC, and local amendments.

Drain sizing

Pipe diameter, slope, and horizontal-versus-vertical rules may change the allowable load.

Venting layout

Trap arm length, wet venting, and fixture order may be treated differently.

Sewer replacement

Materials, cleanout spacing, trench inspections, and connection details may be locally controlled.

Future State Code Lookup

BuildCalc is expanding this page into a state-by-state plumbing code lookup tool. The goal is to help users identify whether their project is likely to fall under UPC, IPC, or a state-specific plumbing code, then link to the proper state or local adoption reference.

Until a state lookup tool is available, the most reliable method is to verify the adopted code directly with the building department for the project address.

Frequently Asked Questions

How do I find out what plumbing code my state uses?

Start with your state building code agency, then confirm with the city or county building department where the project will be permitted. The local authority having jurisdiction is the final source for the adopted plumbing code, edition year, and amendments.

Does every state use the same plumbing code?

No. Plumbing code adoption varies by state and local jurisdiction. Some areas use the Uniform Plumbing Code, some use the International Plumbing Code, and others use a state-specific plumbing code based on a model code with amendments.

Should I follow the state code or the city code?

You normally need to follow the code adopted and enforced by the authority having jurisdiction for the project location. A state may adopt a base code, but a city or county may have local amendments, permit rules, or inspection requirements.

Why does code adoption matter for DFU calculations?

DFU values and pipe sizing rules can differ between UPC, IPC, and local amendments. The same fixture list may produce different sizing results depending on which code and edition applies.

Can an online calculator tell me the final plumbing code requirement?

No. An online calculator can help with early planning, but final pipe sizing, venting, cleanouts, materials, and fixture-unit calculations should be checked against the adopted local code and permit requirements.

What is the authority having jurisdiction?

The authority having jurisdiction, often shortened to AHJ, is the local agency or official responsible for enforcing the building and plumbing code for a project. This is usually the city, county, or local building department.

Important Reminder

This page is for general planning only. Always verify the currently adopted plumbing code, edition year, amendments, and permitting requirements with your local building department before designing or installing plumbing work.

Need help figuring out which plumbing code applies?

Send your project city, county, state, project type, and any building department links you have found. BuildCalc can help organize the code lookup path before you confirm with the local authority having jurisdiction.

Request code lookup help

Continue with plumbing code and DFU resources

Use these related guides to compare UPC and IPC assumptions, estimate fixture loads, check pipe sizing, and understand how local code affects drainage design.