St. Louis's Accessory Structures: The Rules That Matter

Every city handles accessory structures a little differently. In St. Louis, Missouri, there are 9 distinct rules that residents and property owners should be aware of. Some are stricter than what neighboring cities enforce, and others are more relaxed. Here is what you need to know.

Garage Conversions

Converting a garage into livable space in St. Louis requires a Building Division permit, zoning review, and compliance with residential code.

Key details: Permit: Required. Ceiling: Min 7 ft. Egress: 5.7 sq ft window per bedroom. Parking: Zoning review if last space removed. Rental: HCD occupancy permit required.

Unpermitted conversion: $100-$500 plus required retroactive permit or restoration. Cannot legally rent until permitted.

ADU Rules

St. Louis allows accessory dwelling units in many residential zones through a 2023 zoning code update supporting infill housing.

Key details: Permitted Zones: Most single/multi-family districts. Types: Attached, detached, garage conversion. Size Cap: 800 sq ft or 33% of main dwelling. Parking: 1 space (waivers in transit areas). Historic Districts: Cultural Resources review required.

Unpermitted ADU: stop-work order, $100-$500 fine, required to permit retroactively or remove. Life-safety violations are prioritized.

Carport Rules

Carports are treated as accessory structures in St. Louis and must comply with setback, size, and design review rules. Permits are required for any carport regardless of size.

Key details: Permit: Required regardless of size. Placement: Rear/side yard (no front yard). Setback: 3 ft side minimum. Historic Districts: Prefab metal generally disallowed. Enclosure: 3+ sides = garage zoning rules.

Unpermitted carport: $100-$500 and order to permit or remove. Prefab metal carports in historic districts routinely cited and ordered removed.

Tiny Homes

Tiny homes on permanent foundations are allowed in St. Louis as ADUs or primary dwellings subject to zoning district minimums, building code, and historic district review.

Key details: Permanent Foundation: Allowed (as dwelling or ADU). THOW: Not allowed as permanent residence. Code: IRC residential standards. ADU Size: Up to 800 sq ft. Historic Districts: Cultural Resources review.

THOW used as permanent residence: zoning violation, $100-$500 fine and order to remove. Unpermitted construction: stop-work and fines.

Shed Rules

St. Louis allows residential sheds up to 200 sq ft without a building permit but requires zoning compliance under Ord. §26.52. Sheds must be set back at least 3 ft from rear and side lot lines, cannot exceed 12 ft in height, and may not be placed in front yards or easements.

Key details: Permit-Exempt Size: ≤ 200 sq ft, no utilities. Rear/Side Setback: 3 ft minimum. Front Yard: Prohibited. Max Height: 12 ft. Rear Yard Coverage: 30% maximum.

Shed built without required permit: Stop Work Order issued, plus $100-$500 fine under §25.32.990 and possible mandatory removal if the structure cannot be brought into compliance. Setback encroachment: violation notice with 30-day cure; continued violation $100 per day. Shed in front yard: Municipal Code violation, removal typically ordered. Historic district violation without Cultural Resources approval: up to $1,000 fine per offense plus restoration costs.

ADU Owner Occupancy

St. Louis's Zoning Code (SLRC Title 26) does not impose a blanket citywide owner-occupancy mandate on ADUs following the 2021 reforms. However, both the primary dwelling and the ADU, if rented to non-owners, must comply with the City's Occupancy Permit requirement under SLRC Title 25 and any applicable Local Historic District guidelines. Missouri has no state preemption — STL retains full home-rule discretion.

Key details: Citywide Owner-Occupancy: Not required by Title 26. Occupancy Permit: Required per unit (Title 25). Historic Districts: May impose own rules. Permit Agency: Building Division (DPS). State Preemption: None — full home rule.

Renting an ADU without a current Occupancy Permit is a Title 25 violation subject to Building Division enforcement, fines, and inability to lawfully evict for nonpayment until cured. Violations of Local Historic District use restrictions are separately enforced by the Preservation Board.

ADU Rental Restrictions

St. Louis ADUs may be rented long-term (30+ days) subject to the City's Occupancy Permit requirement under SLRC Title 25. Short-term rentals under 30 days are regulated by St. Louis Revised Code Chapter 11.55 (Short-Term Rental Ordinance, Ordinance 71596), which requires a Short-Term Rental Operator Permit and collection of the 3.5% Convention and Tourism Tax plus state and local sales taxes.

Key details: Long-Term Rental: Permitted (Occupancy Permit required). STR Permit: Required (SLRC Ch. 11.55, Ord. 71596). Convention/Tourism Tax: 3.5%. MO Sales Tax: 4.225% + local. Local Contact: Required for STR permit.

Operating an unpermitted STR is a violation of SLRC Ch. 11.55 with administrative fines and potential abatement orders from the Department of Public Safety. Failure to remit hotel/sales tax triggers separate enforcement by the Collector of Revenue and the Missouri Department of Revenue. Local Historic District violations are enforced by the Preservation Board.

ADU Impact Fees

St. Louis does not charge true impact fees on ADUs because Missouri has not granted municipalities statutory authority to impose development impact fees on residential construction. ADU costs are limited to Building Division permit fees, plan-review charges, and Metropolitan St. Louis Sewer District (MSD) and city water connection charges based on actual service.

Key details: Impact Fees: None (MO no state authorization). Building Permit: Per Title 25 fee schedule. Sewer: MSD connection charges only. Water: City Water Division tap fee. School/Park Fees: Not authorized.

Building without permits avoids the official fee schedule but exposes the property to double permit fees on after-the-fact applications, stop-work orders, and Building Division liens. MSD can pursue separate enforcement for unauthorized sewer taps including disconnection.

St. Louis is more permissive than most cities when it comes to adu impact fees. That said, there are still limits.

ADU Permits

St. Louis allows accessory dwelling units in several residential zoning districts following the 2021 ADU reform under Ordinance 71591, which amended the City's Zoning Code (SLRC Title 26). ADU applications are processed by the Building Division within the Department of Public Safety, with zoning review by the City Planning Commission staff. Missouri has no statewide ADU mandate.

Key details: Zoning Code: SLRC Title 26 (Ord. 71591, 2021). Permit Agency: Building Division (DPS). Building Code: 2018 IRC via SLRC Title 25. Historic Review: Preservation Board if in district. State Law: No MO statewide ADU mandate.

Building an ADU without a permit is a violation of SLRC Title 25 and Title 26 subject to stop-work orders and citations from the Building Division. Unpermitted work in a Local Historic District is additionally a Preservation Board violation requiring after-the-fact review. Civil fines under Title 25 escalate for repeat offenses, and the property may be liened until corrected.

The Bottom Line

St. Louis's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming St. Louis is broadly strict or permissive.

Keep in mind that St. Louis can amend these rules at any council meeting. For the most current version of any rule mentioned here, check the specific ordinance page, where we track updates as they happen.