Missouri Plumbing Code

There Is No Single Missouri Plumbing Code

Missouri does not adopt a uniform statewide plumbing code. RSMo Chapter 341 delegates code authority to individual cities and first-class counties, so the technical standards you follow depend on where the project is — not where you hold your license. A plumber crossing a single county line may shift from one IPC edition to another, or from the IPC to a locally modified code altogether.

What Each Major Jurisdiction Adopts

St. Charles County runs the 2021 International Plumbing Code (IPC) as its base, with local amendments compiled in the 2021 St. Charles County Plumbing Code. Exams reference the IPC code family — G27-N or F27-N designations for the master exam.

Jefferson City also tests on the IPC, using ICC exams G28 (Journeyman with Gas) and G27 (Master with Gas).

Springfield adopts the IPC and administers ICC exams through Pearson VUE.

Kansas City references the 2018/2021 International Plumbing Code (IPC) as its base, though local building ordinances layer on modifications. In February 2026, the City Council voted 7–6 to roll back portions of its adopted energy efficiency codes (modeled on the 2021 IECC), relaxing insulation requirements and removing air-leak testing mandates for residential construction.

St. Louis City and St. Louis County each maintain their own locally written plumbing codes rather than adopting a model code directly. St. Louis County's code falls under SLCRO Title XI Chapter 1100, with fee schedule updates tied to Ordinance 29445.

Why This Matters for Licensing

Your exam tests the code your jurisdiction has adopted. A plumber studying the 2018 or 2015 IPC and International Fuel Gas Code (IFGC) for a St. Charles County exam is preparing for different material than someone taking St. Louis County's IAPMO-administered exam on the county's proprietary code. Before you register for any test, confirm exactly which code edition your jurisdiction references — and check whether local amendments are testable.

Code Cycles and the Re-Testing Trap

Jurisdictions update their adopted codes on different schedules, typically every three to six years. St. Charles County ordinances specify that if your plumbing license stays expired for two or more code cycles (six years), you may be required to re-test with the ICC before a new license can be issued. Letting your license lapse through a code update means studying a newer code edition you may never have worked under.

Working Across Jurisdictions

When you bid on a project near a municipal border, verify which jurisdiction holds authority over the project site. Water authorities, sewer districts, and city limits often overlap in the St. Louis metro area. A written confirmation from the local building department about the applicable plumbing code, local amendments, and permit exemptions protects you from stop-work orders and unexpected compliance costs.

The Missouri Plumber License Guide includes a jurisdiction-by-jurisdiction comparison of adopted codes, exam references, and local amendments across seven major Missouri markets.

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