Bolthole Index

Franklin County, Missouri

Building permits, zoning and septic rules in Washington, Missouri

Washington, Missouri requires city building permits for new homes and regulates land use through city zoning districts.12 Inside Washington city limits, a private sewage system needs a written permit from the City Building Official when public sewer is unavailable.3 For land outside the city in Franklin County, county building and zoning requirements apply in unincorporated areas.45

At a glance

Building permits
City building permits required for new construction1
Zoning
City districts and zoning map govern land use2
Septic permits
Written City Building Official approval before constructing a private sewage system where public sewer is unavailable3
RV living and tiny homes
Residential occupancy rules could not be confirmed; ask city Planning and Zoning before buying6
Owner-builder
A city owner-builder exemption could not be confirmed; ask the Building Department7
Agricultural land
AG district farms require at least 10 acres; this is not a citywide residential lot minimum8
Occupancy
Inspection and certificate of occupancy required before occupying residential premises9

Who to call

Building permits

City of Washington Building Department

City building applications, building inspections and occupancy inspections; contact for the City Building Official

636-390-1010

[email protected]

Online permits →

Zoning

City of Washington Planning and Zoning Department

City zoning applications, rezoning, special use permits, variances and parcel zoning questions

[email protected]

405 Jefferson Street, First Floor

Online permits →

Septic permits

City of Washington Building Official

Private sewage disposal system permits and installation inspections inside Washington city limits

Septic permits

Franklin County Building Department

County onsite wastewater approvals; ask whether additional county requirements apply to a proposed private system inside Washington

636-583-6384

400 East Locust Union, MO 63084

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 Washington means bringing your own water and power. The kit we’d start with:

These are affiliate links — we may earn a commission, at no cost to you. As an Amazon Associate, Bolthole Index earns from qualifying purchases.

Does Washington, MO have zoning, lot-size rules and setbacks?

Washington has its own agricultural, residential, commercial, industrial and planned-development zoning districts; the city zoning map determines which district governs a parcel.2 Ask Washington Planning and Zoning to identify the parcel’s district before choosing a home design or farm use.6

In Washington’s AG Agricultural District, a farm must encompass at least 10 acres, and accessory structures housing livestock or fowl must be at least 200 feet from the agricultural district boundary.810 Those thresholds concern AG farms and livestock structures, rather than every residential lot in Washington.810 In the R1-A Single-Family Residence District, the maximum building height is 35 feet or two and one-half stories.11

Do you need a building permit in Washington, and who issues it?

New homes and other new structures inside Washington require city building permits, and Washington has adopted building codes with local amendments.112 Contact the Washington Building Department at 636-390-1010 or [email protected] and apply through the city’s online permit portal.7

Washington’s new-construction building permit calculation uses gross area and ICC modifiers, with a multiplier of $3 per $1,000 of construction cost; the code also requires a $350 refundable escrow until the final certificate of occupancy.13 Request the city’s calculation for your actual plans before setting the construction budget.7 A city owner-builder exemption could not be confirmed; ask the Building Department before assuming that doing the work yourself removes the building permit requirement.7

How do septic permits work inside Washington, MO?

Where public sewer is unavailable, construction of a private sewage disposal system inside Washington requires a written permit signed by the City Building Official before work starts.3 Submit the city application with plans, specifications and any other information the Building Official requests, and pay the permit and inspection fee when filing.3

Washington requires notification before underground portions are covered and when the system is ready for final inspection; installation must satisfy the Building Official.14 Franklin County also administers an onsite wastewater code: ask the county Building Department whether additional county approval applies to your proposed system, while obtaining Washington’s required city approval.15163 Do not begin installation based on an assumed Missouri exemption; the state process requires an issued permit or a confirmed exemption before work begins.17

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

We could not confirm a general rule allowing long-term RV residential occupancy, temporary camping or tiny-home occupancy on private land inside Washington; ask city Planning and Zoning about the proposed address and use before committing to a purchase.6 We also could not confirm a distinct accessory-dwelling rule or minimum dwelling floor area for Washington; include those questions when discussing a small home or second dwelling with the city.6

Washington’s mobile-home provisions require occupied mobile homes to have toilet and bathing facilities and connect to public water and sanitary sewers.18 That mobile-home rule does not establish permission for RV or tiny-home occupancy; obtain a city determination for the particular housing proposal.186

What are the steps to build a home in Washington?

  1. Ask Washington Planning and Zoning to identify the property’s district and review the proposed use against the city zoning map and district rules.26
  2. Confirm sewer availability with the City Building Official; where public sewer is unavailable, obtain the city’s private sewage disposal permit before system construction.3
  3. Create an account in the city permit portal, complete the building application, attach required plans and click Submit so staff receive the application.7
  4. Allow for the city’s stated 2–3 weeks of plan review, with additional time if more information is needed; pay the fees and obtain the issued building permit before scheduling inspections.7
  5. Schedule building inspections by phone, calling by 3 PM the business day before the desired inspection date; online scheduling is unavailable.7
  6. Obtain the required inspection and certificate of occupancy before occupying the Washington home.9

What stays with Franklin County or Missouri, and what should buyers check?

Outside Washington city limits, Franklin County’s Building Department issues building permits for new construction in unincorporated areas, and county Planning and Zoning regulates unincorporated land use.45 Washington’s own building and zoning rules govern the city property described in this guide.12

Missouri requires licensing or permitting of people who construct wells; the available rule does not establish a separate Franklin County homeowner well permit.19 Floodplain development needs approval through the applicable community’s floodplain permitting process, so ask Washington’s city offices about floodplain review before planning construction.206 Franklin County’s soil ratings show only 2.2% rated not limited for conventional septic drain fields; that countywide figure supports budgeting for a site evaluation, rather than assuming septic is impossible or treating the figure as a Washington parcel assessment.21

Watch-outs

  • Washington requires an inspection and certificate of occupancy upon a change of occupancy, so an existing-home purchase can involve city approval as well as a new build.22
  • An agricultural building permit exemption inside Washington could not be confirmed; ask the city Building Department rather than applying an unincorporated-county exemption to city land.7
  • Missouri’s temporary suspension of state onsite wastewater application fees does not establish that Washington’s city permit and inspection fees are waived; Washington’s code requires those fees when filing.233

Sources

  1. Article IV: Supplementary Regulations - City of Washington, MO (Washington), quoted and re-checked
  2. Table of Contents - City of Washington, MO (Washington), quoted and re-checked
  3. Article VI: Private Sewage Disposal Systems - City of Washington, MO (Washington), quoted and re-checked
  4. Building | Franklin County, MO, quoted and re-checked
  5. Planning & Zoning Department, quoted and re-checked
  6. City of Washington Planning and Zoning Department (washmo.gov)
  7. City of Washington Building Department (ci-washington-mo.smartgovcommunity.com)
  8. Article III: District Regulations - City of Washington, MO (Washington), quoted and re-checked
  9. Chapter 500: Building Code - City of Washington, MO (Washington), quoted and re-checked
  10. Article III: District Regulations - City of Washington, MO (Washington), quoted and re-checked
  11. Article III: District Regulations - City of Washington, MO (Washington), quoted and re-checked
  12. Chapter 500: Building Code - City of Washington, MO (Washington), quoted and re-checked
  13. Chapter 500: Building Code - City of Washington, MO (Washington), quoted and re-checked
  14. Article VI: Private Sewage Disposal Systems - City of Washington, MO (Washington), quoted and re-checked
  15. County of Franklin On-Site Wastewater Disposal Code, quoted and re-checked
  16. Franklin County Building Department (franklinmo.gov)
  17. OWTS Construction Permit Process (Missouri statewide rule), quoted and re-checked
  18. Article IV: Supplementary Regulations - City of Washington, MO (Washington), quoted and re-checked
  19. Permits Needed for Well Driller Businesses, quoted and re-checked
  20. Floodplain Forms (Missouri statewide rule), quoted and re-checked
  21. Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
  22. Chapter 500: Building Code - City of Washington, MO (Washington), quoted and re-checked
  23. OWTS Construction Permit Process (Missouri statewide rule), 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 Washington

Washington’s own rules

  • Building permitRequired

    Building or structure construction inside Washington city limits.

    • Appropriate permits and certificate of occupancy must be secured before land preparation or construction.
    • Residential remodels without structural, electrical, or plumbing changes and costing less than $1,000 do not require a building permit.
    “New construction building permits, i.e., commercial buildings, single-family dwellings, one- and two-family dwellings, multi-family dwellings, elevators, swimming pools, garages (attached and detached), pole buildings, storage buildings, etc., shall be computed as follows:”
  • Building code adoptedAdopted

    Construction inside Washington city limits.

    • The adopted codes are amended by Exhibit A to Ordinance 23-13877.
    • The code page states the adopted code is available for public inspection in the City Clerk's office.
    “The following codes are hereby adopted by reference with the amendments referenced in Subsection (B) . below.”
  • InspectionsRequired

    Occupancy inspections and code inspections for residential, commercial, and industrial premises inside Washington city limits.

    • Inspection is required before occupancy and upon change of occupancy.
    • Commercial and industrial structures require annual inspection.
    “For residential dwellings or commercial or industrial structures, an inspection and certificate of occupancy shall be required upon any change of occupancy.”
  • Certificate of occupancyRequired

    Occupancy of commercial, industrial, and residential premises inside Washington city limits.

    • Applications are made to the City Building Official on City forms and applicable fees are due at application.
    • Commercial and industrial certificates are applied for annually.
    • A certificate is invalid if reoccupancy does not begin within 120 days after issuance.

    single-family or two-family inspection fee: 50 USD · multifamily inspection fee: 40 USD

    “It shall be unlawful for any person, owner, corporation or agent to occupy or permit the occupancy of any commercial, industrial or residential premises or structure in the City of Washington without first obtaining an inspection and certificate of occupancy.”
  • Zoning districtsPublished

    Washington city zoning districts.

    • The code publishes AG Agricultural, R1-A, R1-B, R1-C, R1-D, R-2, R-3, commercial, industrial, and planned-development district sections.
    • District boundaries are governed by the City's zoning map and Chapter 400.
    “Section 400.055 AG Agricultural District.”
  • Minimum lot sizeSpecified

    Farms in the AG Agricultural District inside Washington city limits.

    • This is a minimum farm-size rule, not a general minimum residential-lot rule.

    minimum farm size: >= 10 acres

    “Minimum farm size. A farm within an agricultural district shall encompass a minimum of ten (10) acres.”
  • SetbacksSpecified

    Accessory structures used to house livestock or fowl in the AG Agricultural District inside Washington city limits.

    • The setback is measured to the boundary of the agricultural district.

    minimum setback: >= 200 feet (accessory structures used to house livestock or fowl)

    “All accessory structures used to house livestock or fowl shall not be located closer than two hundred (200) feet to the boundary of the agricultural district.”
  • Building heightSpecified

    Buildings in the R1-A Single-Family Residence District inside Washington city limits.

    maximum height: <= 35 feet (or two and one-half stories)

    “Height Requirements. The maximum height is thirty-five (35) feet or two and one-half (2 1/2) stories.”
  • Manufactured homesLimited

    Manufactured/mobile-home occupancy inside Washington city limits, principally in regulated mobile-home-park settings.

    • Mobile-home parks are subject to Chapter 400 requirements.
    • Occupied mobile homes must have toilet and bathing facilities and connect to public water and sanitary sewers.
    • Floodplain placement also requires a floodplain development permit.
    “All occupied mobile homes shall have toilet and bathing facilities and shall be connected to public water supply and sanitary sewers.”
  • Septic permitRequired

    Construction of a private sewage disposal system inside Washington city limits when public sewer is unavailable.

    • Written permit must be signed by the City Building Official before construction.
    • Application must include plans, specifications, and other information requested by the Building Official.
    • Permit and inspection fee are due when the application is filed.
    “Before commencement of construction of a private sewage disposal system, the owner shall first obtain a written permit signed by the City Building Official.”
  • Septic inspectionRequired

    Private sewage disposal system installation inside Washington city limits.

    • Installation must be completed to the Building Official's satisfaction.
    • Applicant must notify the Building Official before underground portions are covered and when ready for final inspection.
    • Inspection is to be made within 24 hours after notice.

    inspection response time: 24 hours

    “The inspection shall be made within twenty-four (24) hours of the receipt of notice by the Building Official.”
  • Permit feesPublished (with conditions)

    City building, utility, demolition, mobile-home setup, inspection, and related permits inside Washington city limits.

    • New construction fee uses building gross area, ICC gross-area modifier, ICC construction-type factor, and a $3.00-per-$1,000 construction-cost permit fee multiplier.
    • A $350 refundable escrow deposit is required until final certificate of occupancy.
    • The code lists minimum fees and a fee schedule adopted December 4, 2023.

    permit fee multiplier: 3 USD per $1,000 construction cost (beginning January 1, 2016) · mobile home setup permit: 200 USD · sewer lateral permit: 40 USD · refundable certificate-of-occupancy escrow: 350 USD

    “The Permit Fee Multiplier shall be set at three dollars ($3.00) per one thousand dollars ($1,000.00) of construction cost beginning on January 1, 2016.”

Still unanswered

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

  • Owner-builder exemption — Owner-builder exemption from Washington city building permits.
  • Minimum dwelling size — Single-family dwellings inside Washington city limits.
  • Lot coverage — Lots inside Washington city limits.
  • Living in an RV — Long-term or residential occupancy of recreational vehicles on land inside Washington city limits.
  • Camping on your land — Temporary camping on private land inside Washington city limits.
4 more unanswered
  • Tiny homes
  • Accessory dwellings
  • Agricultural exemption
  • Driveway access

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 Washington 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