St. Louis, MO Environmental Rules: Stormwater Management (2026)
Key Facts
- Street frontage allowance
- 3,000 sq ft per street frontage
- Alley allowance
- additional 3,000 sq ft
- Excess runoff
- must route to interceptor basins
- Permit required
- for new or resurfaced lots
- Governing code
- amended 2018 IBC § 429
Summary
St. Louis caps how much parking-lot stormwater can drain untreated to the street: 3,000 square feet to street frontage and another 3,000 to an alley, with any excess required to route through interceptor basins under the Plumbing Code.
429.2.5 Drainage. Up to 3,000 square feet of parking and other paved areas shall be permitted to discharge via a driveway to each public or private street frontage and an additional 3,000 square feet shall be permitted to discharge into a public alley. Areas larger than this must have any excess area discharge into interceptor basins as specified in the Plumbing Code.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 11).
Full Breakdown
Section 429 of the City's amended Building Code regulates parking lots and other paved surfaces citywide. Under § 429.2.5, a parking lot or paved area is allowed to discharge up to 3,000 square feet of runoff via a driveway onto each public or private street frontage, plus another 3,000 square feet into a public alley. Any paved area beyond that combined 6,000-square-foot allowance must route its excess runoff into interceptor basins built to Plumbing Code specifications instead of draining onto the street or alley. A building permit is required to construct or resurface a covered parking lot in the first place.
Violations & Fines
Building a parking lot without the required permit, or discharging excess paved-area stormwater onto the street or alley instead of an interceptor basin, is a Building Code violation subject to fines under § 25.33.040.
Frequently Asked Questions
How much parking-lot stormwater can drain straight to the street in St. Louis?
What happens to stormwater beyond the 6,000-square-foot allowance?
Sources & Official References
Other rules in St. Louis
Compare St. Louis to another location·View the Missouri environmental rules overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.