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: up to 900 sq ft (max height: 25 feet). Attached ADU: 700 sq ft. St. Louis ADU regulations are set locally under the St. Louis Revised Code Chapter 26 (Building Code). Detached ADUs (carriage house/alley house) limited to approximately 900 sqft. JADU is a California-specific concept — not applicable in Missouri. St. Louis's alley system and historic coach house tradition make rear-yard ADUs a natural fit.
| Type | Max Size | Max Height |
|---|---|---|
| Detached ADU | 900 sq ft | 25 feet |
| Attached ADU | 700 sq ft | Per primary structure zone height |
Permit Fees
ADU Permit Fees in St. Louis: Plan check fee: $100-$600. Building permit fee: Based on construction value — typically $800-$3,500. Impact fees: None. School fees: None or N/A. Total estimated permit cost: $1,000-$4,500 total permit fees. St. Louis Building Division fee schedule. St. Louis does not have development impact fees. The City's NGA (Neighborhood Stabilization/Vacancy Collaborative) programs may offer incentives for certain infill development.
| Fee Type | Amount |
|---|---|
| Plan Check | $100-$600 |
| Building Permit | Based on construction value — typically $800-$3,500 |
| Impact Fees | None |
| School Fees | None |
| Total Estimate | $1,000-$4,500 total permit fees |
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: 3 feet. Rear setback: 3 feet. St. Louis rear yard setback for accessory structures is typically 3 ft from rear and side property lines. St. Louis's rowhouse and four-flat lots are typically 25-30 ft wide with significant rear yards accessed by alleys. Per St. Louis Revised Code Chapter 26.
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
- ADU must comply with St. Louis Building Code habitability standards
- Detached ADU must be located in rear yard behind the principal structure
- Maximum height 25 ft for detached ADU
- Historic districts (Soulard, Lafayette Square, Tower Grove East) require Board of Adjustment or Cultural Resources review
- Lead paint disclosure required for pre-1978 structures in St. Louis
- Vacant structure rehab projects may qualify for St. Louis Vacancy Collaborative assistance
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
1 ADU per lot
Multifamily Properties
Accessory units on multifamily parcels subject to site plan and Planning Commission review
Historic 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?
No, St. Louis does not require additional parking for ADUs.
Do I have to live on-site to have an ADU in St. Louis?
No, owner-occupancy is not required for ADUs in St. Louis.
Source: St. Louis City Revised Code Chapter 26 (Building); St. Louis Zoning Code (Ordinance 69560). Last verified April 6, 2026. View source