Mississippi Plumbing Code

Mississippi Adopts the International Plumbing Code

Mississippi uses the International Plumbing Code (IPC) as its baseline plumbing standard. Under MS Code Ann. §§ 19-5-9 and 21-19-25, counties and municipalities have building-code and permitting authority, and local adoption determines which IPC edition and amendments apply.

The catch: adoption isn't uniform. Incorporated cities and counties can adopt the IPC directly or amend specific provisions through local ordinance. Under the small-county exception, a county with a total population under 22,000 may opt out of the unincorporated-area permitting requirement through a formal board-of-supervisors resolution; that does not eliminate local master-registration or state-level compliance obligations.

That means the plumbing code you're working under depends on where the job is located.

Which Edition Applies

The IPC updates on a three-year cycle. Mississippi doesn't automatically adopt the latest edition statewide — instead, the adopted edition varies by jurisdiction:

• State exams (MSBOC): The plumbing trade exam administered through PSI is currently based on the 2021 International Plumbing Code. This is the edition you'll study for the state contractor exam.
• Local enforcement: Individual municipalities may be on the 2018, 2021, or even an earlier edition depending on when they last updated their local adoption ordinance. Always confirm the locally enforced edition with the building department before starting work.

When local amendments or a different adopted edition apply, the local rule governs within that jurisdiction, so confirm it with the building department before starting work.

Key IPC Provisions for Mississippi Plumbers

Whether you're studying for the exam or working in the field, these are the IPC sections that come up most frequently in Mississippi plumbing work:

Drain-waste-vent (DWV) sizing. The IPC specifies minimum pipe diameters based on drainage fixture units (DFU). A standard residential bathroom group (toilet, lavatory, bathtub/shower) requires a minimum 3-inch building drain. Getting this wrong is one of the most common rough-in inspection failures.

Horizontal drain slope. Minimum 1/4-inch per foot for horizontal drain lines. Local inspectors measure this during rough-in — a line that looks level to the eye may still fail.

Venting requirements. Every fixture trap must be vented to prevent siphonage. The IPC allows individual vents, common vents, wet vents, and circuit vents depending on the fixture arrangement. Vent pipes must terminate at least 6 inches above the roof and at least 10 feet from any air intake.

Water supply sizing. Based on water supply fixture units (WSFU) and the available pressure from the water main. Under-sized supply lines create flow problems that won't show up until the system is under full demand.

Backflow prevention. The IPC requires backflow prevention assemblies on all cross-connections where non-potable water could enter the potable supply. In Mississippi, the State Department of Health (MSDH) enforces additional cross-connection control regulations — RPZ and DCVA assemblies must be tested annually by an MSDH-recognized tester.

The HB 1163 Permitting Mandate

In 2022, Mississippi House Bill 1163 amended MS Code Ann. §§ 19-5-9 and 21-19-25 to require all counties and municipalities to enforce building permits as a condition of construction — regardless of whether the local jurisdiction has formally adopted building codes.

This was a direct response to historical "unpermitted" work practices in unincorporated county zones. Before HB 1163, a plumber could complete work in some rural areas without any permit or inspection.

The Small-County Opt-Out (HB 1228)

In 2025, HB 1228 created an exception to the universal permitting mandate. Counties with a total population under 22,000 can opt out of the unincorporated-area permitting requirement through a formal board-of-supervisors resolution.

If a rural county opts out, the local building department won't administer a standard structural permit process for unincorporated areas. But the state plumbing code still applies as a standard of care — performing substandard work that violates the IPC can still result in MSBOC license suspension or civil penalties, even if no local inspector ever visits the site.

Before starting work in an unincorporated area, verify with the county whether they've opted out. The answer determines whether you need a local permit or not.

Exam vs. Field Application

For the MSBOC plumbing trade exam, you're tested on the 2021 IPC specifically — pipe sizing calculations, DWV isometric analysis, backflow standards, and OSHA safety compliance. The exam is open-book, so you can bring a tabbed and highlighted copy of the IPC to the testing center.

In the field, you're applying whichever edition the local AHJ has adopted. Inspectors evaluate your work against the locally enforced code, which may include amendments that differ from the exam edition.

The Mississippi Plumber License Guide covers both the exam-relevant IPC content and the practical field application across Mississippi's patchwork of local code adoptions.

See more Mississippi guides →