ADU laws in Missouri

In plain words

Missouri has no statewide ADU law. An ADU, or accessory dwelling unit, is a smaller second home on the same lot as a house. It could be a backyard cottage, an apartment over a garage, or a unit attached to the house. In Missouri, each city, town, village and county decides whether to allow ADUs. They decide through zoning. Zoning is the local rulebook for what can be built where. So the rules can change from one town to the next. Several large cities now allow ADUs. Since 2025, St. Louis allows one ADU by right in its residential zones. By right means staff approve it if it meets the written rules, with no public hearing. Kansas City allows ADUs on lots with a detached house. Its rules require the owner to live in the house or the ADU. That rule is called owner occupancy. Springfield's new code allows ADUs in all single-family zones. Columbia eased its rules in June 2026. Smaller towns and counties may ban ADUs or require a special permit. Some have no ADU rule at all. As of October 2026, no statewide ADU bill had passed, and none was pending. A 2026 bill to set permit deadlines also failed. A homeowners association (HOA) rule can block an ADU, too. So can a deed restriction, which is a limit written into your property's deed. Check with your local planning office before you design anything. You may be able to build only if local rules and your property allow it.

The rules at a glance

What to do next

1. Find out whether your property is inside city limits or in unincorporated county land; that decides which zoning code applies.
2. Look up your zoning district and read the local ADU or accessory-dwelling rules, or call the planning office and ask what is allowed on your lot.
3. Ask about owner-occupancy rules, size caps, setbacks, parking, and long-term and short-term rental limits before you design, since these vary the most across Missouri.
4. Read your deed and any HOA covenants; private restrictions can ban a second unit even where zoning allows one.
5. If your home uses a septic system or private well, contact the agency that permits them early to learn whether they can serve a second unit.
6. Get zoning and building permits before construction starts. In Kansas City, ask about the city's free pre-approved plan for an ADU over a garage.

What your town still decides

No Missouri statute requires cities or counties to allow ADUs. Cities, towns and villages get zoning power from RSMo Chapter 89 (§89.020), and county commissions may adopt planning and zoning for unincorporated areas under Chapter 64, where different sections apply to different classes of county (for example §64.090 covers certain first-class counties). Each local government decides whether ADUs are allowed, where, how big, whether the owner must live on site, and whether approval is by right or needs a special or conditional use permit. Whether land is inside city limits or in the unincorporated county decides which rules apply. Several large cities loosened their rules between 2022 and 2026 (Kansas City 2022, St. Louis 2025, Springfield 2025, Columbia 2026). We found no ADU bill in the Missouri House or Senate bill lists for the 2023 through 2026 sessions. In 2026, bills that would have set statewide deadlines for issuing building permits (HB 1791, SB 1286 and related bills) and a bill to stop towns from banning manufactured homes (HB 3230) did not pass. HOA covenants and deed restrictions can also forbid a second unit. On rural lots, septic and well capacity is often the real limit.

Examples of local rules

• St. Louis (city): Board Bill 60, Ordinance 72036, passed September 26, 2025 and signed by the mayor at the end of that month (the city lists it as effective September 29, 2025), allows attached and detached ADUs by right in residential zones on lots with a single-family, two-family or semi-detached home. One ADU per parcel, up to the greater of 750 sq ft or 50% of the largest home on the lot, never over 1,200 sq ft, and no taller than 25 feet. No off-street parking is required for the ADU. It must be at least 3 feet from side lot lines, and a detached unit at least 10 feet from the house. Details come from the bill text as introduced; confirm the final ordinance. Source
• Kansas City: Ordinance 220698, passed September 15, 2022 (Zoning Code §88-305-15), allows an ADU on any lot where a detached house is the main building. Attached units go in the side or rear yard and detached units in the rear yard, 5 feet from lot lines. A detached ADU may be no larger than 800 sq ft or 90% of the main home's floor area, whichever is smaller. No extra parking is required. The owner must live in the house or the ADU and record a deed restriction saying so; the ordinance asked staff to revisit that rule after a year. A June 2023 rewrite of the same section (Ordinance 230552) kept the owner-occupancy and deed rule and added a height cap for detached units of 25 feet or the house's height, whichever is lower. The city also offers free pre-approved house plans, including an ADU over a garage. Source
• Springfield: City Council adopted a new Community Land Development Code on March 24, 2025, that allows ADUs in all single-family districts, subject to design and operating conditions. The city said full implementation would follow zoning map updates in spring 2026. Check the adopted code for size, parking and occupancy rules. Source
• Columbia: City Council passed Ordinance 026337 (Council Bill B142-26, Case 113-2026) on June 15, 2026, effective on passage. Per the Planning and Zoning Commission's May 7, 2026 recommendation, it lets ADUs be built in the R-1 district without a conditional use permit. The ordinance sets a single 5,000 sq ft minimum lot area, caps an ADU at 800 sq ft or 75% of the house (whichever is smaller) and three bedrooms, adds a parking space only for ADUs with three or more bedrooms, and lets only one unit on an R-1 lot be a registered rental. Source

What we’re still confirming

• St. Louis's final ADU ordinance (No. 72036) may differ from the bill as first introduced; confirm details with the city.
• Kansas City, Missouri, re-adopted its owner-occupancy rule in June 2023; confirm it still applies.

Laws, bills and citations

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.