Bolthole Index

Franklin County, Missouri

Building permits, zoning and septic rules in Union, Missouri

Union, Missouri requires city building permits for new structures and structural work, and the city administers its own zoning.12 In Franklin County, Union’s city building office is the starting point for construction inside city limits; we could not confirm which office issues septic permits for a Union address, so ask the city and Franklin County Building Department before planning private sewage disposal.13

At a glance

Building permits
City building permits required for new structures and structural work1
Zoning
Union has its own zoning code2
Residential lot size
R-1: 12,000 square feet; R-2: 7,500 square feet45
Building permit fees
Residential project cost multiplied by 0.0035, plus a $25 administrative fee6
Floodplain work
Additional city floodplain permit; $100 special permit fee7
Septic permits
City-address authority unconfirmed; ask the city and county building offices13

Who to call

Building permits

City of Union Building & Engineering Department

City building permits, plan review and inspections; starting point for city zoning and floodplain questions

(636) 583-1805

[email protected]

10 E. Locust Street - Union, MO 63084

Septic permits

Franklin County Building Department

County on-site sewage program contact; confirm jurisdiction for a Union city address before applying

636-583-6384

Contact details are copied from each office’s official page and were checked against it on October 12, 2026.

Off-grid gear

Going off-grid in Union means bringing your own water and power. The kit we’d start with:

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Do you need a building permit in Union, MO?

Union requires a city building permit for work creating a new structure or affecting an existing building’s structure or structural supports, including projects such as decks, sheds, garages and swimming pools.1 Union adopts the International Building Code, 2021 Edition, with local changes.8 Report the proposed project to Union’s Building & Engineering Department before work begins: the city’s residential guidance says construction cannot commence until a building permit has been acquired.1 We could not confirm a city owner-builder exemption; ask the building office about your proposed work rather than assuming doing the labor yourself removes the building-permit requirement.1

Who issues building permits in Union, and what do they cost?

Union’s Building & Engineering Department handles city construction applications and inspections; use the city office for a project inside Union city limits.1 Union’s residential building-permit calculation uses total project cost multiplied by 0.0035, and the residential administrative fee is $25 and non-refundable.6 Water and sewer fees are separate from building fees, although the city adds them to the building permit payment for new construction needing hookups.1 Union requires 24 hours’ notice for building inspections, so arrange inspections with the building office as construction progresses.1

Does Union have zoning, lot-size rules and setbacks?

Union administers its own zoning code, so establish the parcel’s district before deciding what home will fit.2 For single-family dwellings in Union’s R-1 district, minimum lot area is 12,000 square feet and minimum width at the established building line is 90 feet.4 In Union’s R-2 district, the corresponding minimums are 7,500 square feet and 65 feet.5 Union’s R-2 front yard must be at least 25 feet, including along every street on a lot with multiple frontage; the side yard must be at least 10% of lot width and no less than 8 feet.9 Ask the city to check your plot plan against the parcel’s actual district before purchasing a house design.1

How do septic permits work inside Union?

We could not confirm the septic-permit authority for land inside Union; ask Union’s Building & Engineering Department and Franklin County Building Department to identify the responsible office for the exact address.13 Missouri requires a construction permit before installing or repairing most onsite wastewater systems, although some single-family residential lots may be exempt; work should wait until a septic permit is issued or an exemption is confirmed.10 Union’s building guidance treats water and sewer hookups as separate charges from the building permit.1 Resolve sewer availability and whether private sewage disposal is acceptable with the city before committing to a septic design.1

Can you live in an RV or tiny home in Union?

We could not confirm residential RV occupancy, temporary camping, tiny-home occupancy or a minimum dwelling floor area inside Union; ask the city building office about the proposed use and the parcel’s zoning before buying a unit or moving onto the land.1 Union has a zoning code, and city building permits are issued only when other regulations and zoning restrictions are satisfied.21 Union’s residential district lot-area rules describe the lot, rather than establishing a tiny home’s minimum interior floor area.45 Request an answer for your specific dwelling and occupancy plan.

Building a home in Union: what should you do first?

Start with Union’s Building & Engineering Department and resolve the parcel’s zoning and proposed use before submitting the construction application; city building-permit issuance depends on compliance with zoning and other regulations.1 Next, prepare a plot plan showing lot dimensions and proposed development distances to property lines, plus 2 sets of detailed drawings.1 Submit the building-permit application with those plans and estimated construction cost, then obtain the building permit before starting construction.1 Arrange required inspections with advance notice and ask about the final and occupancy inspection.1 For floodplain work in Union, obtain the additional city floodplain permit, whose special permit fee is $100.7 For land outside Union city limits, use the Franklin County guide: county zoning applies to unincorporated land.11

Watch-outs

  • Union floodplain work requires a special city floodplain permit in addition to any building, right-of-way or other required permit.7
  • We could not confirm a Union owner-builder or agricultural building exemption; ask the city building office before treating either as exempt.1
  • We could not confirm Union’s sewer-connection requirement or septic jurisdiction for a city address; settle both with the city and county building offices before buying land for private sewage disposal.13

Sources

  1. City of Union Building & Engineering Department (unionmissouri.gov)
  2. Table of Contents - City of Union, MO (Union), quoted and re-checked
  3. Franklin County Building Department (franklinmo.gov)
  4. City of Union, MO Single-Family Dwelling Districts (Union), quoted and re-checked
  5. Article V: "R-2" Single-Family Dwelling District (Union), quoted and re-checked
  6. Article III: Fees - City of Union, MO (Union), quoted and re-checked
  7. Article III: Fees - City of Union, MO (Union), quoted and re-checked
  8. Article I: Adoption of Building Codes - City of Union, MO (Union), quoted and re-checked
  9. Article V: "R-2" Single-Family Dwelling District (Union), quoted and re-checked
  10. OWTS Construction Permit Process (Missouri statewide rule), quoted and re-checked
  11. Planning & Zoning Department, quoted and re-checked

Written October 12, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.

Answers from the rulebook for Union

Union’s own rules

  • Building permitRequired

    Construction, erection, alteration, or modification of an existing structure inside Union city.

    • All proposed work must first be reported to designated City officials.
    • If the County Assessor determines improvements of less than $1,000 increased value by $1,000 or more, the applicant must obtain a permit.
    “Thereafter, the applicant shall be required to obtain a permit and to have the work inspected by the Building Inspector.”
  • Building code adoptedAdopted

    Building construction and structures inside Union city.

    • The adopted code is the International Building Code, 2021 Edition.
    • Section 500.020 provides additions, insertions, deletions, and changes.

    code edition: International Building Code, 2021 Edition

    “A certain document, one (1) copy of which is on file in the office of the City Engineer of the City of Union, being marked and designated as the International Building Code, 2021 Edition, as published by the International Code Council Inc., be it hereby adopted as the Building Code of the City of Union, Missouri, for the control of building and structures as herein provided;”
  • InspectionsLimited

    Certain improvements to structures inside Union city.

    • For improvements initially valued below $1,000, inspection and a permit become required if the County Assessor determines the improvements increased building value by $1,000 or more.
    • The Building Inspector must determine whether work complied with applicable Codes.

    assessor value threshold: >= 1000 USD (applies after improvements initially valued below $1,000)

    “Thereafter, the applicant shall be required to obtain a permit and to have the work inspected by the Building Inspector. If the Building Inspector determines that the work was not performed in accordance with all applicable Codes, the applicant shall cause such work to be redone so as to meet Code requirements.”
  • Local zoningPresent

    Land inside Union city, Missouri; the City publishes and administers Chapter 405, Zoning Code.

    “Chapter 405 Zoning Code (Section 405.010 – Section 405.870)”
  • Minimum lot sizeSpecified

    Single-family dwellings in the City of Union R-1 District.

    • The lot must also have at least 90 feet of width at the established building line.

    minimum lot area: >= 12000 square feet · minimum lot width: >= 90 feet (at the established building line)

    “Every single-family dwelling, convent, monastery, rectory, or parish house shall be on a lot having an area of not less than twelve thousand (12,000) square feet and a width at the established building line of not less than ninety (90) feet in the "R-1" District.”
    One more reviewed finding on this topic
    • Specified — Single-family dwellings in the City of Union R-2 District.
      “Every single-family dwelling, convent, monastery, rectory, or parish house shall be on a lot having an area of not less than seven thousand five hundred (7,500) square feet and a width at the established building line of not less than sixty-five (65) feet.”
  • SetbacksSpecified

    Single-family dwellings in the City of Union R-2 District.

    • Front yard is required on all streets for a lot with multiple frontage.
    • Side yard is at least 10 percent of lot width and not less than 8 feet.
    • Rear yard is the larger of 25 feet or 20 percent of lot depth, capped at 35 feet.
    • A nonconforming lot of record may be used if specified front, side, and rear yard requirements are met.

    front yard: >= 25 feet (required on all streets where a lot has multiple frontage) · side yard: >= 10% of lot width (not less than 8 feet) · rear yard: 25 feet or 20% of lot depth, whichever is larger (not exceeding 35 feet)

    “Front Yard. Not less than twenty-five (25) feet. Where a lot has multiple frontage, the required front yard shall be required on all streets.”
  • Building heightSpecified

    Single-family dwellings in the City of Union R-1 District.

    • Single-family dwellings may increase height by not more than 10 feet to a maximum of three stories when side and rear yards are each increased by at least 10 feet over district requirements.

    maximum height: 35 feet (may increase by not more than 10 feet under stated yard and story conditions)

    “Single-Family Dwellings — Thirty-Five (35) Feet. Single-family dwellings may be increased in height by not more than ten (10) feet to a maximum height of three (3) stories when the side and rear yards are increased over the yard requirements of the district by not less than ten (10) feet each.”
    One more reviewed finding on this topic
    • Specified — Single-family dwellings in the City of Union R-2 District.
      “Single-family dwellings — thirty-five (35) feet. Single-family dwellings may be increased in height by not more than ten (10) feet to a maximum height of three (3) stories when the side and rear yards are increased over the yard requirements of the district by not less than ten (10) feet each.”
  • Subdividing landRegulated (with conditions)

    Subdivision and land division inside Union city.

    • The chapter includes preliminary plats, final plats, improvements, street standards, lot identification, recording of plats, and water and sewer requirements.
    “Section 410.060 Preliminary Plats. Section 410.070 Final Plat. Section 410.080 Improvements.”
  • Building in a floodplainRequired

    Work completed in a floodplain inside Union city.

    • The floodplain permit is additional to any building, right-of-way, or other required permit.
    • The City code cross-references Chapter 415, Flood Damage Prevention.

    special floodplain permit fee: 100 USD (additional to other required permits)

    “Any work being completed in a floodplain requires a special permit. The fee for this additional permit, which is required in addition to any building, right-of-way, or other required permit, shall be one hundred dollars ($100.00).”
  • Permit feesPublished (with conditions)

    Building, water, sewer, floodplain, development, grading, and related permits inside Union city.

    • Residential building permits use total project cost multiplied by 0.0035.
    • Residential administrative building-permit fee is $25; commercial and industrial administrative fee is $75.
    • Floodplain work requires an additional $100 special permit fee.
    • Water and sewer permits have separate administrative and connection fees.

    residential administrative building permit fee: 25 USD (non-refundable) · commercial or industrial administrative building permit fee: 75 USD (non-refundable) · residential new-building multiplier: 0.0035 (applied to total project cost) · floodplain special permit fee: 100 USD (additional permit required in addition to other required permits)

    “The administrative fees for building permits shall be collected at the time of the filing of a petition or an application and shall be non-refundable. Administrative fees for residential-related permits shall be twenty-five dollars ($25.00) and for commercial and/or industrial-related permits the fee shall be seventy-five dollars ($75.00).”

Still unanswered

We looked and could not find an official answer yet. Silence is not permission; ask Union or Franklin County directly.

  • Owner-builder exemption — Owner-builders performing construction inside Union city.
  • Certificate of occupancy — Certificates of occupancy for land and buildings inside Union city.
  • Minimum dwelling size — Single-family dwellings inside Union city; R-1 and R-2 dimensional provisions were reviewed, but no minimum floor-area rule was located.
  • Lot coverage — Lot coverage for development inside Union city.
  • Living in an RV — Long-term or residential RV occupancy inside Union city.
13 more unanswered
  • Camping on your land
  • Tiny homes
  • Manufactured homes
  • Accessory dwellings
  • Who permits septic
  • Septic permit
  • Septic inspection
  • Off-grid sanitation
  • Well permit
  • Mandatory utility hookup
  • Agricultural exemption
  • Driveway access
  • Short-term rentals

Each answer was extracted from an official source and independently re-checked against that source by a second reviewer. That is an evidence check, not legal advice. Rules change; confirm with the authority before you buy or build.

Unanswered questions are usually a sign that Union publishes no rule on the point, not that none exists. Franklin County’s page lists the county offices to call.

← All of Franklin County: county rules, score and offices