St. Louis County, MO Building Setbacks & Zoning: Lot Coverage Limits (2026)
Key Facts
- Accessory coverage cap (R districts)
- 7% of lot area
- Single accessory structure size cap
- 400 sq ft or 50% of house footprint
- Combined accessory ceiling
- 1,000 sq ft per lot
- Commercial (C-3) building coverage cap
- 25% of lot area
- Detached garages allowed
- 1 per single-family home
- Other detached accessory structures
- 2 (3 counting garage)
Summary
St. Louis County does not cap the total footprint of a single-family house on its lot, but it does cap everything else built around it. Detached accessory structures like sheds, garages, and pool houses may cover no more than 7% of the lot in every residential district, while commercial C-3 parcels face a flat 25% building-coverage ceiling.
B.Detached above-ground accessory structures shall be subject to the following design criteria:(1)Detached above-ground accessory structures shall not cover more than a total of seven (7) percent of the lot area.(2)Any detached accessory structure...may be up to four hundred (400) square feet in area, or fifty (50) percent of the building footprint of the primary structure, whichever is greater.(3)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 on which it is located. ["C-3" District] 8.Development limitations.(1)No more than twenty-five (25) percent of the total area of any lot or tract of land in this district shall be covered by structures.
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
B(1), governing accessory structures in the "R-1" Residence District, caps detached above-ground accessory structures at seven (7) percent of total lot area, and the identical 7 percent figure repeats verbatim in the R-6A district and elsewhere in Chapter 1003. That percentage cap stacks with per-structure size limits in the same subsection: any single detached accessory structure may run up to 400 square feet or 50 percent of the primary structure's footprint, whichever is greater, but the combined footprint of all accessory structures on one lot can never exceed 1,000 square feet regardless of lot size, and no more than one detached garage and two other detached accessory structures (three counting the garage) are allowed per single-family home.
8(1) limits the "C-3" Shopping District to no more than 25 percent of the total lot area covered by structures of any kind. St. 158, for parcels that opt into that zoning classification rather than the standard district regulations.
Violations & Fines
A shed, detached garage, or other accessory structure that pushes total accessory coverage past 7 percent of the lot, exceeds the 400-square-foot/50-percent-footprint cap, or breaks the 1,000-square-foot combined ceiling will be denied a building permit by the Department of Planning. Structures already built past these limits can be ordered reduced or removed, and owners who need relief must seek a variance from the Board of Zoning Adjustment.
Frequently Asked Questions
Is there a maximum lot coverage percentage for houses in St. Louis County?
How big can my shed or detached garage be in St. Louis County?
Does commercial property have a different coverage limit than houses?
Sources & Official References
Other rules in St. Louis County
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