Building permits, zoning and land rules in St. Charles County, Missouri

Yes. Unincorporated St. Charles County requires a residential building permit for projects such as detached single-family homes, mobile home installations and modular homes, with applications submitted through the Citizenserve portal¹. Like most counties around it in Missouri, St. Charles County requires a county building permit¹. County-administered construction follows the 2021 I-Codes and 2020 National Electric Code with amendments¹². Submit contractor information, building plans, a plot plan and estimated construction cost; review typically takes about 10 working days¹. At least one inspection is required, and the permit card identifies the inspections for the job¹³. The residential building permit fee is the greater of a $60 minimum or 0.0073 times estimated construction cost; floodplain, land-disturbance and other fees can be added, and a $40 reinspection fee applies after three inspections¹⁴. Property inside incorporated Weldon Spring needs a land-use permit from that town instead¹. An agricultural land-use permit exception covers qualifying construction, alteration, repair and regrading under 5,000 square feet, but it does not establish an exemption from building, septic or floodplain permits⁷. An owner-builder exemption could not be confirmed, so ask Building and Code Enforcement before planning do-it-yourself work^13,15.

The St. Charles County Building and Code Enforcement Division handles residential building permits in county-administered areas; call 636-949-7345, email bce@sccmo.org, or visit 201 N. Second St., Suite 412, St. Charles, Missouri¹³. The Planning & Zoning Division answers parcel-specific zoning questions at 636-949-7335 or planning@sccmo.org from Suite 420 at the same address¹⁶. Building and Code Enforcement also handles county septic and floodplain permits^5,13. The Highway Department handles work in county-controlled or county-maintained road right-of-way at 636-949-7305 or highway@sccmo.org^17,18. Inside the City of Saint Charles, the city's own Community Development department administers zoning under Chapter 400 of its Municipal Code³. Inside Foristell, the city adopts and administers its own zoning, while septic permits for Foristell addresses still come from St. Charles County^4,19.

Yes. St. Charles County administers zoning in unincorporated areas under Chapter 405 of its Unified Development Ordinance and the county zoning map, and has used zoning since 1959². Incorporated cities run their own: the City of Saint Charles zones under Chapter 400 of its Municipal Code³, and Foristell adopts its own zoning regulations⁴. The county rules below apply only to unincorporated land. The county zoning map and GIS show parcel-level districts, so confirm the district with Planning & Zoning before designing a house or dividing land^8,16. In the A Agricultural District, a single-family dwelling needs at least 800 square feet of living space¹⁰. A Agricultural lots generally need 5 acres and 150 feet of width, subject to ordinance exceptions¹⁰. Principal structures in that district generally have 50-foot front and rear yards and 40-foot side yards, with different standards for certain small lots and other stated conditions¹⁰. Land divisions into lots of at least 5 acres in A, R or RR districts outside existing subdivisions may use a minor subdivision plat; other divisions require preliminary and final plats⁸. Lot coverage and building height remain parcel-specific questions for Planning & Zoning¹⁶.

The St. Charles County Building and Code Enforcement Division regulates onsite wastewater treatment systems in unincorporated St. Charles County and contracting jurisdictions⁵. A county septic permit is required to install, alter, expand or repair a system, except for specified filter work, pressure adjustments and like-equipment replacements⁹. The residential minimum fee is $150, and a private sewage disposal operating permit is listed at $75¹⁴. Septic permits cover every address the county serves, including Foristell¹⁹. Sanitary waste must use public sewer where applicable or an onsite system where public sewer is unavailable²⁰. Only about 3.9% of county soils rate without severe limitations for a conventional drain field, so establish septic feasibility before fixing the house location²¹. Missouri guidance says some single-family lots may be exempt from the state process, but St. Charles County has its own local permit rule for county-administered land^9,22. The county identifies inspections at transfer of ownership but does not establish a universal inspection interval for every onsite system²⁰.

St. Charles County does not allow an RV as unrestricted permanent housing under the reviewed rule. Temporary recreational shelter is allowed only on a parcel or in a subdivision platted before January 1, 1973 in the PR or A districts, or within a campground, and requires a Planning and Zoning permit⁶. RV occupancy is limited to 180 days per calendar year and one RV per parcel outside an approved campground or travel trailer park⁶. The RV must be highway-ready and have approved water, sewage and power arrangements⁶. A specific tiny-home occupancy rule could not be confirmed; a tiny home used as a dwelling still faces county building-permit and zoning review^1,8. Off-grid living does not bypass sanitation rules because an approved onsite system is still required where public sewer is unavailable⁵.

1. Confirm that the parcel is unincorporated, identify its zoning district and obtain the applicable standards from Planning & Zoning^8,16.
2. Determine whether public sewer serves the site; otherwise establish onsite wastewater feasibility and obtain the county septic permit before locating the house^9,20.
3. Check the regulated floodplain; covered development needs a separate floodplain permit, and qualifying construction must place the lowest finished floor at least 1 foot above base flood elevation²³.
4. Secure access; driveway work in county road right-of-way needs an advance county Special Use Permit, while a state highway entrance needs a MoDOT permit¹⁷.
5. Submit contractor information, plans, a plot plan and estimated cost through Citizenserve¹.
6. Complete the inspections listed on the permit card¹³.

Put septic feasibility near the top of due diligence because only about 3.9% of St. Charles County soils rate without severe limitations for a conventional drain field²¹. Confirm the zoning district before relying on an advertised dwelling type, setback, RV use or subdivision plan^8,16. Check mapped flood hazards because construction, improvements, demolition and earthmoving in regulated areas can require a floodplain permit even when no building permit is required, and a floodplain permit taken separately from a building permit is effective for 2 years²³. Verify whether the road is county- or state-controlled before designing access because the issuing authority changes with the right-of-way¹⁷. Budget beyond the purchase price: the median property-tax bill is about $3,340 a year at an effective rate near 1.1%, while typical home insurance is about $2,072 a year²¹. The complete private-well permit process could not be confirmed, so ask Building and Code Enforcement which water approvals apply to the parcel¹³.