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2026 Cost Guide · Updated June 2026

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

St. Louis's 2023 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)
9–14 yrsTypical payback period
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 front elevation
Missouri Detached ADU
Missouri Garage Conversion ADU
Missouri Attached ADU
Missouri Basement Conversion ADU
Missouri Modular Prefab ADU
Missouri ADU kitchen interior
Missouri ADU living room interior
Missouri ADU bedroom interior
Missouri ADU bathroom interior
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
At a Glance

Missouri ADU costs — by type.

Detached ADU
$85K – $220K
St. Louis and Kansas City skew highest
🏡
Attached ADU
$80K – $190K
Shares one wall; easier approval path in most cities
🔗
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
📦
💡

No statewide ADU law — rules vary by city. Missouri has no statewide ADU law. St. Louis passed Board Bill 60 permitting ADUs by-right in all residential zones in 2023–2024. Kansas City and Columbia each maintain their own separate zoning codes and ADU provisions.

Calculate My ROI →
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.

🏛️
St. Louis Board Bill 60
St. Louis's 2023–2024 zoning ordinance permits ADUs by-right in all residential zones, removing the discretionary approval process that previously slowed projects.
By-right in all residential zones
🎓
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
🏘️
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
📋
City-by-City Rules
No statewide ADU law. St. Louis, Kansas City, and Columbia each set their own zoning, size limits, and permitting processes.
Varies entirely by city
Homeowners reviewing ADU permit documents
Permits & Fees

What permitting actually costs.

Missouri has no statewide ADU permit standard. Each city sets its own fees, calculated on project valuation.

📄
Building Permit Fee — KC / St. Louis
$1,000 – $2,500
Typical range for a standard ADU application in the two largest metros.
🏗️
Building Permit Fee — Other Cities
$500 – $2,000
Varies significantly by city and project value.
💧
Utility Connection Fees
$3,000 – $18,000
Water, sewer, and electrical connections. Varies widely by municipality.
🧾
Impact / Development Fees
$0 – $6,000
Not charged in every city; verify with your local planning department.
⏱️
Permit Review Timeline
4 – 10 weeks
Varies by city and whether the project requires special use review.
Missouri Law
There's no state-level protection here.

Missouri has no single statewide ADU statute — ADUs are regulated at the local level through city and county zoning codes. St. Louis, Kansas City, and Columbia each have their own formal ADU provisions.

Statewide ADU lawNone
St. Louis size cap800 sq ft
St. Louis approvalBy-right in residential zones
Owner-occupancy requirementVaries by city
Permit review timeline4–10 weeks
Best rental marketSt. Louis
💡 Verify your specific city's ADU ordinance first

St. Louis, Kansas City, and Columbia each set their own zoning, size limits, and permitting processes — and unincorporated county land often has separate rules again. A quick call to your local planning department before design work begins prevents costly redesigns later.

Return on Investment

What a Missouri ADU returns.

$900–$1,700
Monthly rental income range statewide
9–14 yrs
Typical payback period (detached)
Meaningful equity boost
Added property value
4–10 wks
Typical permit review timeline
St. Louis Metro
$1,050 – $1,700/mo
1-bed monthly rent
9–12 years
Estimated payback
Kansas City Metro
$1,000 – $1,600/mo
1-bed monthly rent
9–13 years
Estimated payback
Columbia / Boone County
$900 – $1,350/mo
1-bed monthly rent
10–14 years
Estimated payback · Mizzou demand
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 →
Compact detached ADU exterior
🏡
Compact Detached ADU
Missouri — statewide range
Added Property Value
Meaningful equity boost
1
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
2
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
3
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
4
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
5
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
6
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
7
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. Missouri has no statewide ADU law — rules and costs vary by city.
Does Missouri have a statewide ADU law?
No. Missouri has no single statewide ADU statute — ADUs are regulated at the local level through city and county zoning codes. St. Louis, Kansas City, and Columbia each have their own formal provisions; unincorporated county land can differ again.
Are ADUs allowed by-right in St. Louis?
Yes. St. Louis's Board Bill 60, passed in 2023–2024, 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?
Permit review timelines in Missouri typically run 4–10 weeks depending on city and whether the project requires special use review. St. Louis's by-right process is generally the most straightforward.
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?
Kansas City and St. Louis typically charge $1,000–$2,500 for ADU permits. Other Missouri cities generally charge $500–$2,000. Always request an itemized fee estimate from your specific city.
What is the ROI on an ADU in Missouri?
Missouri ADUs generate $900–$1,700 per month depending on market. Payback periods run 9–14 years. Columbia's University of Missouri-driven rental demand supports especially strong occupancy near campus.

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Cost Disclaimer: All cost ranges and estimates are approximations based on industry contractor data, published reports, and regional market research as of 2026. Actual ADU costs vary significantly based on lot conditions, city requirements, contractor selection, material specifications, and design complexity. Missouri has no statewide ADU law — rules vary entirely by city and zoning district. Always verify current zoning and permit requirements directly with your local authority before beginning design. Always obtain a minimum of three contractor bids before committing to a project budget. Last updated June 2026.