Franklin County, Missouri Building Permit Guide

For land outside city limits, the Franklin County Building Department, 400 E. Locust Street, Room 006, Union (636-583-6384), issues building, electrical, mobile home and septic permits and inspects the work under the 2021 International Codes and the 2020 National Electrical Code, in force since April 23, 2024. Every application starts with a $25 processing fee, most permits also carry a refundable escrow paid by separate check, and starting work before the permit is issued doubles the fee.

Franklin County building department: who handles permitting

The Building Department’s office is open Monday to Friday, 8 a.m. to 4:30 p.m., and inspectors are in the office from 8 to 8:30 a.m. and 3:30 to 4 p.m. (7 to 7:30 a.m. and 2:30 to 3 p.m. from Memorial Day to Labor Day) to answer questions about a particular inspection. Zoning, subdivision and floodplain matters belong to the Planning & Zoning Department in the same building (636-583-6369), which administers the county’s Unified Land Use Regulations.

Inside a city or village, that municipality decides. Populations below are Census Bureau Vintage 2025 estimates for the part of each place in Franklin County.

What needs a county permit

The Building Department posts applications for building permits, commercial plan review, multi-use buildings, mobile homes, sewer (septic) systems, solar installations, pools, storage buildings and electric service upgrades, plus a driveway declaration. The county’s amendments to the 2021 International Residential Code change the list of work that needs no permit:

The county also deleted the 2021 code’s requirement for automatic fire sprinklers in homes.

Franklin County permit fees

Work the flat-rate list does not cover is calculated by the department, with a minimum calculated construction permit fee of $150. Escrow is paid by separate check and is refunded within one month of the passed final occupancy inspection. Under Commission Order 2024-139, a residential permit whose fee is over $1,500 carries a $500 escrow instead of $350 and runs 18 months instead of 12; any permit can be extended by paying one-eighth of the fee for 3 months, up to one-half for 12 months. If the permit lapses without a final occupancy inspection the escrow goes to the county general fund, and no new permit is issued on that parcel until the old one passes. Starting construction before the permit is issued doubles the fee, and the department may also ask for sealed as-built plans.

What to bring with a house application

• A signed application and a site plan
• Two sets of plans with the footing and foundation plan, floor plans, elevations and a wall section showing rafter, stud and joist sizes and the rebar in the walls
• Truss details from the lumber company and any engineered joist layout
• The electrical and mechanical specification sheet
• A soil test where needed, the sewer design and the installer’s name, or a central sewer letter
• The recorded deed number if the land was bought recently, and the Ameren premise number

The department will not accept incomplete plans. It also checks whether the parcel has an expired permit from the last five years that never passed its final inspection, because no new permit can be issued until that one is closed. Storage buildings and detached garages of 300 sq ft or more follow a separate checklist, and structural steel needs plans sealed by a Missouri design professional.

How to get a Franklin County building permit

Inspections

Inspections are scheduled or cancelled only through the office line, 636-583-6384, not by inspectors or voicemail, and must be called in by 2:30 p.m. the day before. The approved plans with the inspection card attached must be on site. Footings, pier pads and foundation walls are inspected formed, with steel tied, before concrete is poured, and drywall before it is taped. If work is covered without an inspection, the county issues a stop work order and charges 25% of the original permit fee, and inspections resume only after the owner provides a sealed design professional’s statement or uncovers the work.

Septic, floodplain and code changes

Septic systems: the Building Department is also the county’s onsite wastewater authority, under the On-Site Sewage Disposal Systems Ordinance adopted and amended on September 23, 2025 and effective October 1, 2025. An application needs a plot plan, sewer design, soil evaluation where required and a signed affidavit naming the installer, and the fee is due when you apply.

Floodplain and streams: the county takes part in the National Flood Insurance Program, with flood maps dated June 5, 2020. Planning & Zoning issues floodplain development permits ($250 including the elevation certificate review). Article 11 of the Unified Land Use Regulations requires new or substantially improved homes to have the lowest floor, basement included, 2 ft above the base flood elevation, and sets stream buffers of 100 ft from the top of the bank on perennial streams and 50 ft on intermittent ones. A zoning permit or zoning verification is $35 under the schedule in force since February 2022; a revised Planning & Zoning fee list was reviewed at the October 22, 2026 workshop and goes to the Commission for approval.

Data centers: on September 15, 2026 the Commission added data center and accessory data center regulations to the Unified Land Use Regulations (Commission Order 2026-254) and, the same day, approved rezoning requests from Diamond 66, Diamond Farms and BLE Landholdings. A resident’s proposed one-year moratorium on data center development was tabled at the August 13, 2026 workshop and listed again for the August 20 workshop; no outcome has been posted.

Missouri building code

Missouri has no mandatory statewide building code for private construction: a county, fire protection district or municipality may adopt one (usually by reference under RSMo 67.280), and in parts of the state none has. Building codes in Missouri

Franklin County permit FAQs

Who issues building permits in unincorporated Franklin County?

The Franklin County Building Department, 400 E. Locust Street, Room 006, Union (636-583-6384).

Do I need a permit for a shed in Franklin County?

Not for a one-story detached building of 300 sq ft or less. A carport or prefab building over 300 sq ft fastened to concrete needs one.

How much does a deck permit cost?

$150, plus the $25 application fee and a $200 escrow that is refunded after the final inspection.

What happens if I start before getting a permit?

The permit fee is doubled, and sealed as-built plans from a Missouri design professional may be required.

Does the county issue permits in Washington or Union?

No. Washington, Union, Pacific, Sullivan, St. Clair, New Haven and Gerald run their own permits, and the Village of Parkway approves its own.

Who handles septic permits?

The county Building Department; a residential new or repair permit is $135 plus a $200 escrow.

Franklin County permit search and official resources

• Franklin County Building Department: applications and adopted codes
• Franklin County Building Department fee schedule (2024)
• Franklin County permit escrow requirements
• Franklin County inspection information form
• Franklin County single-family application checklist
• Franklin County amendments to the 2021 Residential Code
• Franklin County On-Site Sewage Disposal Systems Ordinance (2025)
• Franklin County Planning & Zoning and Unified Land Use Regulations
• Franklin County Planning & Zoning fee schedule
• Franklin County Commission agendas and packets
• FEMA Community Status Book: Missouri
• City of Pacific Building Department
• City of Sullivan Building & Code Department
• City of St. Clair Building Department
• City of New Haven Building Department

Simplify Franklin County permitting with Alliance Permitting

Alliance Permitting is a permit documentation and submission company in Missouri. We prepare your paperwork, file it correctly and coordinate with the permitting authority through issuance. We are not a contractor and we do not perform licensed plan review or inspections; that work stays with your licensed team and the jurisdiction.

This guide is provided by Alliance Permitting for general information about Franklin County permitting. Requirements, fees, and procedures change; confirm details with the permitting authority before relying on them.