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.
Whether ADUs are allowed in St. Louis, MO has not been confirmed — see the official source before proceeding.
Whether St. Louis, MO permits accessory dwelling units (ADUs) has not been confirmed from an official source. ADUs — also called granny flats, in-law units, or secondary suites — are secondary housing units on a single-family or multifamily lot. Contact the local building department through their official website to verify current ADU rules before proceeding, as regulations may have changed since this data was last reviewed.
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: Permit timeline has not been confirmed — contact the department for current processing times. Apply through the local building department online permit portal. Contact them through their official website for current contact information.
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: Parking requirements have not been confirmed — see official source.
Restrictions & Requirements
How Many ADUs Are Allowed?
Number of ADUs Allowed in St. Louis: Single-family lots: not confirmed — see official source. Multifamily properties: not confirmed — see official source.
- 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 detailsFrequently 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