2026 Cost Guide · Updated September 2026

ADU Cost in Missouri — St. Louis, Kansas City, Columbia & Statewide

St. Louis's 2025 by-right ADU ordinance and Kansas City's growing rental market create strong opportunities across the Show-Me State. City-by-city cost data across St. Louis, Kansas City, and Columbia — built from permit records, contractor data, and regional labor rates.

$85K–$220KDetached ADU range

$45K–$100KGarage conversion (lowest cost)

HUD FY2026Adopted rent benchmark

No state lawRules set city-by-city

MISSOURI
ADU Collection

Beautiful. Functional. Built for Missouri Living.

🏠Increase Property Value

💲Generate Rental Income

👥Multi-Generational Living

🌿Sustainable Design

Missouri ADU outdoor living and patio space

Planning & Inspiration

Planning Reference

Example 1-bedroom ADU floor plan, illustrative layout

Example Floor Plan

Illustrative 1-bedroom layout. Actual floor plans vary by ADU type, size, local code, and homeowner needs.

Missouri ADU exterior at twilight, warm interior light glowing

Missouri ADU and main house evening backyard view

Aerial view of Missouri property with backyard ADU

Homeowners reviewing ADU permit documents

Permits & Fees

What permitting actually costs.

Missouri has no statewide ADU-siting law; St. Louis and a handful of other cities allow ADUs by-right, but most jurisdictions still require discretionary review. City, county, zoning, building, utility, and site rules control. The detailed figures below are representative planning ranges, not a statewide fee schedule or review-time guarantee.

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Building Permit Fee — KC / St. Louis

$1,000 – $2,500

Typical range for a standard ADU application in the two largest metros.

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Building Permit Fee — Other Cities

$500 – $2,000

Varies significantly by city and project value.

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Utility Connection Fees

$3,000 – $18,000

Water, sewer, and electrical connections. Varies widely by municipality.

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Impact / Development Fees

$0 – $6,000

Not charged in every city; verify with your local planning department.

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Permit Review Timeline

4 – 10 weeks

Varies by city and whether the project requires special use review.

Verified September 17, 2026 · Local control

Local rules control

Missouri has no statewide ADU-siting law; St. Louis and a handful of other cities allow ADUs by-right, but most jurisdictions still require discretionary review.

Legal classificationLocal control

Governing frameworkLocal rules control

Representative permit fees$500 – $2,000

Representative review time4 – 10 weeks

Local verificationRequired

Source: NationwideADU 51-jurisdiction law directory →

Verify the property before design

These are planning benchmarks, not a permit quote, eligibility ruling, or legal opinion. Confirm zoning, building, utility, site, private-covenant, fee, and timing requirements with the current local authorities. See the 51-jurisdiction law directory and national permit guide.

ADU Types

Which type fits your property?

01 / Most Common

Detached ADU

$85K – $220K

Freestanding backyard structure. St. Louis's by-right zoning ordinance has expanded eligibility citywide, pushing typical project size and cost toward the top of the range.

Detached ADU Guide →

02 / Most Affordable

Garage Conversion

$45K – $100K

Uses an existing structure to cut cost significantly versus new detached construction while generating similar rental income in most Missouri markets.

Garage Conversion Guide →

03 / Fastest Build

Modular / Prefab

$75K – $185K

Factory-built construction offers a faster, more predictable timeline than custom stick-built projects across Missouri's markets.

Prefab ADU Overview →

04 / Easier Approval

Attached ADU

$80K – $190K

Generally an easier approval path than detached units in many Missouri jurisdictions, and shares one wall with the primary residence to reduce site-work cost.

Attached ADU Guide →

05 / Common Statewide

Basement Conversion

$50K – $115K

Basement apartments are common across Missouri's older St. Louis and Kansas City housing stock, offering a cost-effective conversion path in established neighborhoods.

Basement ADU Guide →

Cost by Region

Every Missouri market is different.

St. Louis Metro

St. Louis City · St. Louis County

$95K–$220K

$142–$275 per sq ft

Highest cost

Kansas City Metro

Jackson · Platte counties

$90K–$210K

$135–$262 per sq ft

Moderate

Columbia / Boone County

University of Missouri area

$85K–$180K

$128–$225 per sq ft

More affordable

Cost Factors

Why Missouri ADUs cost what they cost.

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St. Louis Board Bill 60

St. Louis's September 2025 zoning ordinance (Board Bill 60 / Ordinance 72036) permits ADUs by-right in all residential zones, removing the discretionary approval process that previously slowed projects.

By-right in all residential zones

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University Rental Demand

The University of Missouri concentrates strong, recurring rental demand in Columbia, supporting steady ADU occupancy near campus.

Drives Columbia campus-area demand

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Older Housing Stock

Missouri's established St. Louis and Kansas City neighborhoods have a high share of homes with existing basements and garages suited for conversion.

Favors conversion projects

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Current ADU Legal Framework

Missouri has no statewide ADU-siting law. St. Louis's Board Bill 60 allows ADUs by-right, but most other Missouri jurisdictions still require discretionary review. City, county, zoning, building, utility, and site rules control.

Local control · Local rules control

At a Glance

Missouri ADU costs — by type.

Detached ADU

$85K – $220K

St. Louis and Kansas City skew highest

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Attached ADU

$80K – $190K

Shares one wall; easier approval path in most cities

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Garage Conversion

$45K – $100K

Most affordable; uses existing structure

🚗

Basement Conversion

$50K – $115K

Common across Missouri's older housing stock

⬇️

Modular / Prefab

$75K – $185K

Fastest construction timeline

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💡

Local control: Local rules control. Missouri has no statewide ADU-siting law; St. Louis and a handful of other cities allow ADUs by-right, but most jurisdictions still require discretionary review. Permit fees and review timing remain planning estimates until confirmed for the specific property.

Calculate My ROI →

Return on Investment

Missouri ROI planning inputs.

$825–$1,100

Adopted statewide 1-bedroom rent range

15%

National property-value planning input

10%–20%

Property-value uncertainty range

30%

Operating-expense planning reserve

Rent source

HUD FY2026 revised

One-bedroom FMR market basket

Exact HUD mappings

ROI-CM-1.4

Home-value source

Statewide Zillow ZHVI

June 30, 2026

One statewide input

Not a valuation

Payback period

Calculated live

Budget, ADU type, size and rent

Open calculator →

No static statewide promise

Full methodology

Transparent sources

HUD, Census PUMS, Zillow and FHFA

Review methodology →

Planning estimate, not a valuation

Save Money

7 ways to cut your
Missouri ADU cost now.

Missouri is already one of the more affordable states to build in — these moves push savings further and prevent the most common costly mistakes.

Calculate My ADU ROI →

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Compact Detached ADU

Missouri — statewide range

Property-Value Planning Input

15%

Convert before you build new

If your property has a qualifying garage or basement, start there — conversions cost significantly less than detached new construction while generating similar rental income.

Saves substantially vs. new construction

Build in St. Louis for the simplest approval path

St. Louis's Board Bill 60 permits ADUs by-right in all residential zones — no discretionary approval or public hearing required, unlike some other Missouri jurisdictions.

Avoids discretionary-approval delays

Get a minimum of three contractor bids

Contractor pricing for ADU projects in Missouri varies significantly for equivalent scope. Getting three bids from ADU-experienced contractors is the most reliable way to avoid overpaying.

Prevents overpaying for the same scope

Start design during permit review

Begin contractor research during the permit review period — not after approval. Experienced ADU contractors in St. Louis and Kansas City book several months in advance.

Cuts weeks off total project timeline

Explore financing options before you start

HELOC, cash-out refinance, and ADU-specific loan programs all have different costs and qualification criteria. Choosing the right option can save thousands over the project's life.

Can save $10,000–$40,000 over project life

Verify your city's zoning and size limits first

St. Louis, Kansas City, and Columbia each set their own ADU size caps and rules. A feasibility check before design work begins prevents thousands in wasted design fees.

Prevents wasted design fees

Target campus-adjacent Columbia neighborhoods for demand

University of Missouri enrollment supports especially strong, consistent rental demand in Columbia's campus-adjacent neighborhoods.

Supports stronger occupancy and rents

Frequently Asked Questions

Missouri ADU answers.

How much does an ADU cost in Missouri?

ADU costs in Missouri range from $45,000 for a basic garage conversion to $220,000 for a large detached new build in St. Louis or Kansas City, the most expensive markets.

Does Missouri have a statewide ADU law?

No. Missouri has no statewide ADU-siting law; ADU rules are set entirely at the city and county level, and requirements vary widely across the state. St. Louis (Board Bill 60) and a handful of other cities have adopted by-right ADU ordinances, but most Missouri jurisdictions still require discretionary review. City, county, zoning, building, utility, and site rules control. Local zoning, building, utility, site, and private-covenant requirements may still apply; verify the current rules for the property before design or construction.

Are ADUs allowed by-right in St. Louis?

Yes. St. Louis's Board Bill 60 (Ordinance 72036), passed by the Board of Aldermen in September 2025 and signed by Mayor Cara Spencer on September 30, 2025 (effective September 29, 2025), permits both attached and detached ADUs by-right in all residential zones, removing the discretionary approval process required in many other Missouri jurisdictions.

How long does it take to get an ADU permit in Missouri?

The representative ADU permit-review planning timeline for Missouri is 4 – 10 weeks. This is not a statewide deadline or guarantee. Timing can change with the local authority, project complexity, corrections, utilities, site conditions, and application completeness; confirm the current timeline locally.

What is the cheapest ADU to build in Missouri?

Garage conversions are generally the least expensive option, typically $45,000–$100,000, using an existing structure to significantly cut cost versus new detached construction.

How much are ADU permit fees in Missouri?

The representative ADU permit-fee planning range for Missouri is $500 – $2,000. This is not an official statewide fee schedule or quote. Plan review, utility, impact, site, and other local charges may be additional; request a current itemized estimate from the permitting authority.

What is the ROI on an ADU in Missouri?

The adopted Missouri one-bedroom planning range is $825–$1,100 per month, derived from the HUD FY2026 revised FMR market basket under ROI-CM-1.4. Payback is calculated from the homeowner's budget, ADU type, size, rent range, and a 30% operating-expense reserve. Property value uses a 15% national planning input with a 10%–20% uncertainty range; it is not a valuation.

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Planning Disclaimer: Cost, fee, and timeline ranges are approximations for education and early planning; actual requirements and costs vary with the property, local authority, utilities, site conditions, design, and contractor. The Missouri legal classification and framework shown here were verified on September 17, 2026, but they do not determine parcel eligibility and are not legal advice. Confirm current zoning, building, utility, private-covenant, fee, and timing requirements directly with the applicable authorities before design or construction. Obtain at least three contractor bids before committing to a project budget. Last updated September 2026.