St. Louis County, MO Accessory Structures: Shed & Carport Rules (2026)
Shed permit rules in St. Louis County, MO, also referred to as storage shed, backyard shed, or accessory building regulations, set size limits, setbacks, and when a building permit is required.
Key Facts
- Permit-exempt shed size
- Up to 120 sq ft (11.15 m2)
- Exemption source
- § 1115.101, amended IBC § 105.2, Item 3
- Zoning per-structure cap
- 400 sq ft or 50% of house footprint
- Aggregate accessory cap
- 1,000 sq ft regardless of lot/house size
- Lot coverage cap
- 7% for all detached accessory structures
- Structure count limit
- 2 accessory structures (3 with a garage)
Summary
A detached, one-story storage shed, tool shed, or playhouse in unincorporated St. Louis County needs no building permit as long as its floor area stays at or under 120 square feet under the county's amended IBC Section 105.2; go over that, and the full building-permit process applies.
105.2 Work exempt from permit. Exemptions from permit requirements of this code shall not be deemed to grant authorization for any work to be done in any manner in violation of the provisions of this code or any other laws or ordinances of this jurisdiction. Permits shall not be required for the following:...3.One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided the floor area does not exceed 120 square feet (11.15 m 2).
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 85 | Traffic: Supplement 80).
Full Breakdown
St. Louis County adopted the International Building Code, 2015 edition, with local amendments codified at Section 1115.101, and one of those amendments rewrites Section 105.2's list of work exempt from permit. Item 3 on that list exempts "one-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided the floor area does not exceed 120 square feet (11.15 m2)" from needing a building permit at all. A shed that clears 120 square feet loses that exemption entirely and must go through the standard building permit process administered by the county's Department of Transportation and Public Works, including plan review and inspection.
The permit exemption is only half the picture; the Zoning Ordinance layers its own size and placement caps on top of it. In the "NU" Non-Urban and other residential zoning districts, Section 1003.107's accessory-structure design criteria say a detached accessory structure, including a "detached storage/utility shed," may be up to 400 square feet, or 50 percent of the primary structure's footprint, whichever is greater, but "no structure or aggregate of all accessory structures shall exceed one thousand (1,000) square feet in gross floor area, regardless of the size of the primary structure or the size of the lot." Detached accessory structures together also can't cover more than 7 percent of the lot, an owner may have at most two detached accessory structures (three counting a garage), and no accessory building is allowed in the front yard.
Violations & Fines
Building a shed over 120 square feet without first obtaining a building permit under Section 1115.101's amended Section 105.2 is a code violation subject to stop-work and correction orders from the county's building code enforcement staff; exceeding the zoning code's 1,000-square-foot aggregate accessory-structure cap or the two-structure limit in Section 1003.107 is a separate zoning violation enforced by the Department of Planning.
Frequently Asked Questions
Do I need a permit to build a shed in St. Louis County?
Is there a maximum size for a shed even if I get a permit?
How many sheds or accessory buildings can I have?
Can I put a shed anywhere on my lot?
Sources & Official References
Other rules in St. Louis County
How St. Louis County compares: Shed Permit Requirements by City·Compare St. Louis County to another location·View the Missouri accessory structures overview
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