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Accessory Structures

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

By CityRuleLookup Editorial Team

Every city handles accessory structures a little differently. In St. Louis, Missouri, there are 2 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.

ADU Rules

St. Louis allows one attached or detached accessory dwelling unit per residential parcel, capped at 25 feet in height and 1,200 square feet, and set back at least 3 feet from side lot lines under the zoning code's 2025 ADU standards.

Key details: Max height: 25 feet. Max size: 1,200 sq ft. Units per parcel: one (attached or detached). Side setback: 3 feet minimum. Off-street parking: not required for ADU.

Building an ADU that doesn't meet these standards is a zoning-code infraction punishable under Chapter 1.12's general penalty (§ 26.100.010); the City Counselor can also sue to force compliance under § 26.100.020.

Shed & Carport Rules

St. Louis exempts small detached sheds from a building permit only if they are 120 square feet or less, under 12 feet tall, anchored to a 4-inch concrete slab, and set back per the Zoning Code.

Key details: Permit-exempt size: 120 sq ft or less. Permit-exempt height: Under 12 feet. Foundation required: 4-inch concrete slab, anchored. Setbacks: Must still meet Zoning Code yards. Hazardous-use sheds: Permit required over 50 sq ft.

Building without a required permit is enforceable by the Building Commissioner as a code violation, including stop-work orders and citation fines under Chapter 25; a shed placed inside a required yard setback is a zoning violation the Zoning Administrator can order corrected or removed regardless of size.

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.