Building permits, zoning and septic rules in Platte County, Missouri

Unincorporated Platte County, Missouri requires a building permit before covered construction, alteration, repair, moving, demolition or occupancy changes; ordinary repairs and certain portable-equipment connections are excepted¹. Starting work before issuance can trigger doubled fees and a stop-work order, subject to the stated emergency exception¹. Unincorporated Platte County uses amended 2018 building, residential, plumbing, mechanical, fuel-gas, energy-conservation and swimming-pool codes, plus the 2017 electrical code¹. For homes up to 1,400 square feet, the published building-permit fee is $200 for the first 500 square feet or part thereof, plus $.25 per additional square foot; larger homes use a different schedule¹. We could not confirm a general owner-builder exemption; ask Planning & Zoning^4,7. City building permits come from Parkville⁸, Weatherby Lake⁹, Weston¹⁰, Lake Waukomis¹¹, Dearborn¹² inside their respective limits. Septic jurisdiction is separate: ask Platte County Health Department to confirm the authority for the address³.

Platte County Planning & Zoning handles building permits and zoning for unincorporated Platte County; call 816-858-3338 or email permits@co.platte.mo.us, or visit 415 Third Street, Suite 016, Platte City, Missouri⁷. Select “Building Permit Application” through a county website account and upload complete plans and supporting documents¹; the packet states that review and action occur within 5 working days after all required information arrives⁷. Residential applications require septic or sewer documentation, a water-district availability letter and an entrance permit where applicable^1,7. County building inspections cover footing, prebackfill, ground rough, rough-in and final stages¹. Occupancy must wait for road and wastewater approvals, the required affidavit and a certificate of occupancy¹.

Unincorporated Platte County has county-administered zoning, and a use that the parcel’s district does not authorize, or a special use without its approval, is prohibited². Identify the parcel’s district on the Official Zoning Map filed with the County Clerk². Municipal zoning applies inside Parkville¹³, Platte City¹⁴, Riverside¹⁵, Weatherby Lake¹⁶, Weston¹⁷, Lake Waukomis¹⁸, Edgerton¹⁹, Dearborn²⁰, Kansas City²¹, Smithville²²; Kansas City reaches into Platte County mainly from Jackson County, and Smithville mainly from Clay County^21,22. Septic jurisdiction remains a separate address check with Platte County Health Department³. In Platte County’s AG district, dwellings generally need 100-foot front and rear yards and 30-foot side yards on interior lots; exceptions apply². Other districts have their own area regulations, and in a planned residential development the setbacks are negotiated and recorded on the final plat before approval, then enforced². In AG or RE, 1 accessory dwelling is allowed on at least 5 acres with an existing principal single-family home; the accessory dwelling cannot exceed the principal home’s floor area excluding its attached garage, must meet dwelling setbacks and share a driveway, and may need HOA approval².

Unincorporated Platte County’s principal-dwelling lot minimums include 40 acres in AG, 5 acres in RE, 80,000 square feet in R-80 and 40,000 in R-40². Smaller residential districts have their own minimums and common-area provisions, so use the parcel’s actual classification². The RTD two-family district allows 5,000 square feet per dwelling unit, or 7,500 square feet for a single-family dwelling², and the RMD multiple-dwelling district also sets 7,500 square feet for a single-family dwelling². Ask Planning & Zoning about older-lot boundary-line exceptions and subdivision approval before dividing land or relying on a smaller tract^1,2,7.

Unincorporated Platte County construction using septic tanks requires a Platte County Health Department septic permit; public-sewer properties use the applicable sewer approval instead¹. Call Environmental Health at 816-858-2412 for onsite permits, exemptions and inspections; the county ordinance may require more than Missouri’s minimum standards^3,7. Residential sewer approval may come from Platte County Regional Sewer District or Timber Creek Sewer Company, depending on service¹. The Regional Sewer District permit the county lists for commercial applications is a sewer connection permit, not approval of onsite septic systems¹. About 11.9% of county soils are rated “not limited” by USDA for conventional drain fields; evaluate the site before placing the house, because a low share does not mean septic is impossible²³. Inside Platte City, Riverside, Weston, Edgerton and Dearborn, city codes also require private-sewage permits and inspections while preserving additional health-authority requirements^{24,25,26,27,28}.

We could not confirm a general rule allowing long-term RV occupancy, temporary private-land camping or tiny-home occupancy in unincorporated Platte County; ask Planning & Zoning about the proposed unit, occupancy period and wastewater plan⁷. A mobile-home dwelling inside a regulated mobile-home park must have at least 500 square feet, excluding open porches, breezeways and garages; that threshold does not establish a countywide minimum home size². Travel trailer camps need a Special Permit, are allowed only in AG and CH, and require at least 5 acres for short-term occupancy by the traveling public; those camp rules do not establish permission for household RV living on private land².

1. Confirm the district, allowed dwelling type, lot minimum and setbacks with Planning & Zoning^2,7.
2. Establish the water and wastewater approval path, including the residential water-availability letter and septic or sewer permit¹.
3. Confirm the road authority and obtain an entrance permit where applicable; new entrances in unincorporated Public Works District #1 require a county entrance permit^7,29.
4. Obtain a separate floodplain-development permit before development in a regulated flood zone³⁰.
5. Upload the complete online building application, plans and approvals, pay the building-permit fee, and wait for issuance before construction¹.
6. Complete required inspections and driveway surfacing, then obtain the certificate of occupancy before moving in^1,31.

Platte County reviews new plats and subdivisions for infrastructure, so ask Planning & Zoning about approval before buying a proposed land split^1,7. Driveways generally must match the accessed road surface and be at least gravel before occupancy; agricultural or single-family lots larger than 2 acres are excepted from matching unless the road-maintenance authority requires it³¹. Missouri permits landowners to install their own well or pump without an installer permit, but public wells need written approval and private-well requirements vary by category and location; confirm the water plan with Missouri DNR and county Planning & Zoning^5,6,7. Regulated flood-zone development requires separate approval and additional elevation, utility and sewage safeguards^30,32. Platte County's effective property-tax rate is about 1.1%, with a median annual bill near $3,365²³.