ADU Rules in St. Louis, MO (2026)
ADU rules, permit requirements, size limits, and fees for St. Louis, MO. Source-cited from official municipal code.
Yes, ADUs are allowed in St. Louis, MO.
St. Louis, MO permits accessory dwelling units (ADUs) on residential properties. ADUs — also called granny flats, in-law units, backyard cottages, or secondary suites — are secondary housing units on a single-family or multifamily lot. State and local law governs the approval process. In St. Louis, the St. Louis Building Division (Community Development Administration) handles ADU permit applications. Below you will find the current size limits, setbacks, fees, and timeline for building an ADU in St. Louis.
ADU Size Limits
ADU Size Limits in St. Louis: Detached ADU: size varies by zoning — see official source (max height: varies — see official source). Attached ADU: size varies by zoning — see official source.
| Type | Max Size | Max Height |
|---|---|---|
| Detached ADU | See official source | See official source |
| Attached ADU | See official source | See official source |
Permit Fees
ADU Permit Fees in St. Louis: Plan check fee: Varies. Building permit fee: Varies. Impact fees: None. School fees: None or N/A. Total estimated permit cost: Varies.
| Fee Type | Amount |
|---|---|
| Plan Check | See official source |
| Building Permit | See official source |
| Impact Fees | None |
| School Fees | None |
| Total Estimate | See official source |
Permit Timeline
St. Louis ADU Permit Timeline: St. Louis Building Division permit review: typically 4-8 weeks. Construction 3-9 months. The St. Louis Vacancy Collaborative and New Roots program may offer expedited review for eligible properties. Apply through the St. Louis Building Division (Community Development Administration) online permit portal. Phone: (314) 622-3313.
Setback Requirements
ADU Setback Requirements in St. Louis: Front setback: follows zone standard. Side setback: no minimum. Rear setback: no minimum.
Parking Requirements
Parking Requirements: No additional parking required for ADU under St. Louis current code. St. Louis's grid neighborhood design with alley access means most parcels have rear parking available regardless.
Restrictions & Requirements
How Many ADUs Are Allowed?
Number of ADUs Allowed in St. Louis: Single-family lots: 1 ADU per lot. Multifamily properties: Accessory units on multifamily parcels subject to site plan and Planning Commission review. St. Louis has a significant inventory of multi-family buildings (four-flats, rowhouses) — ADU rules for single-family vs. multifamily parcels differ. St. Louis is also notable for its large number of vacant structures being rehabbed as part of the City's comeback strategy.
- Single-Family Lots
- See official source
- Multifamily Properties
- See official source
Statewide Preemption
ADU Preemption
We could not confirm a statewide ADU preemption statute for Missouri.
View Missouri preemption detailsHistoric District Considerations
Historic District Requirements: St. Louis has 9 historic districts where additional design review may be required for ADU construction. Design review approval is required before obtaining a building permit for properties in historic overlay zones. St. Louis Preservation Board administers local historic districts including Soulard, Lafayette Square, Compton Heights, Tower Grove East, and several others. Certificate of Appropriateness required for exterior changes in designated districts. St. Louis also has National Register historic districts that provide federal historic tax credit opportunities. The City's Cultural Resources Office provides guidance. St. Louis has one of the largest concentrations of 19th-century brick architecture in the United States. Look up historic district boundaries at: https://stlouis-mo.gov/government/departments/planning/cultural-resources.cfm
Frequently Asked Questions
Can I build an ADU in St. Louis?
Yes. St. Louis, MO allows accessory dwelling units. On a single-family lot you can build 1 ADU per lot.
How big can an ADU be in St. Louis?
The maximum size for a detached ADU in St. Louis is 900 square feet.
How long does it take to get an ADU permit in St. Louis?
The typical ADU permit timeline in St. Louis is St. Louis Building Division permit review: typically 4-8 weeks. Construction 3-9 months. The St. Louis Vacancy Collaborative and New Roots program may offer expedited review for eligible properties.. Total estimated permit fees are $1,000-$4,500 total permit fees.
Do I need extra parking for an ADU in St. Louis?
St. Louis parking rules for ADUs: No additional parking required for ADU under St. Louis current code. St. Louis's grid neighborhood design with alley access means most parcels have rear parking available regardless.
Do I have to live on-site to have an ADU in St. Louis?
Owner-occupancy requirement in St. Louis: No state-mandated owner-occupancy requirement. St. Louis City regulations do not impose owner-occupancy for ADU approval.
Source: St. Louis City Revised Code Chapter 26 (Building); St. Louis Zoning Code (Ordinance 69560). Last verified April 6, 2026. View source