Bolthole Index

Columbia County, Washington

Zoning, building permits and septic rules in Dayton, Washington

The City of Dayton, Washington adopts and administers its own zoning code1. Columbia County Planning and Building handles building permits and inspections inside the city2, and the county's Public Health office reviews septic systems and connections to public sewer3. Rules for land outside city limits differ; see the Columbia County page.

At a glance

Zoning
City of Dayton's own zoning code (Title 11)1
Building permits
Issued by Columbia County Planning and Building for city addresses2
Septic
Columbia County Public Health reviews and approves plans3
Minimum lot (AR zone)
10,800 square feet4
Maximum height
35 feet to the roof5
Accessory dwellings
Allowed with limits; register with the city planning department6
Owner-builder
Exempt from contractor registration, not from permits7

Who to call

Planning & zoning

City of Dayton City Hall (planning review)

Planning review of building permit applications and land use permits (conditional use, variance, short subdivision, site plan review) inside Dayton

(509) 382-2361

111 S 1st Street Dayton, WA 99328

Building permits

Columbia County Planning and Building

Building permits and inspections for the county and for the City of Dayton

(509) 382-4676

115 E Main St. Dayton, WA 99328

Septic permits

Columbia County Public Health, Environmental Health

Environmental Health questions, including septic systems and individual wells

(509) 382-2181

[email protected]

112 N 2nd St Dayton, WA 99328

Contact details are copied from each office’s official page and were checked against it on October 24, 2026.

Off-grid gear

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

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Does Dayton, Washington have zoning, and what does it mean for lot size and setbacks?

Yes. The City of Dayton adopts and administers its own zoning code, Title 11 of the city code, for land inside the corporate limits1. Title 11 publishes residential, commercial, industrial and open space districts, and the city links an official zoning map from its website8.

Two residential districts matter most to a home builder. In the Agricultural Residential (AR) zone, the minimum lot area is 10,800 square feet4, and front and rear yard setbacks for principal buildings are 20 feet9. In the Urban Residential (UR) zone, the table shows no minimum lot area, with a 50-foot minimum lot width and 100-foot minimum lot depth10, and front and rear setbacks of 10 feet11.

Buildings in both districts top out at 35 feet to the roof512. Building lot coverage is capped at 40 percent in AR and 50 percent in UR1314. The same Title 11 table lists side and corner-lot setbacks, so read it for your exact lot9.

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

Building permits for Dayton addresses come through Columbia County, not a separate city building department. The city's own site says Columbia County provides all building-related services for the City of Dayton, including building permits, inspections and code questions2. The county department confirms it provides building services for the City of Dayton15.

Submit the application to Columbia County Planning and Building, and the city's site also says applications must go to City Hall for planning review2. Call15 at (509) 382-4676 for the form and fee estimate.

The county applies a building permit requirement to building, plumbing, mechanical and electrical work, with exemptions such as small accessory structures16. That is the county's rule for its own permits; we could not confirm the exact exemptions the city applies to its addresses, so ask the county office before assuming a shed or small project is exempt. Washington's owner-builder exemption covers contractor registration only, not building permits7.

How do septic permits work for a home in Dayton?

Septic permits in this part of Washington go through Columbia County Public Health, which reviews and approves plans for wells, septic systems and connections to public water and sewer systems3. The application is a Master Application for On-Site Sewage Disposal Permit, and the county asks for soil reports, water quality tests and site plans17.

Washington requires a permit from the local health officer before installing, modifying or expanding an on-site sewage system, except for minor repairs18. Inside a sewer service area, state rules can require connection to public sewer when it is available within 200 feet19.

We could not confirm whether every Dayton address is on city sewer or whether the city sets its own connection rule. Call Columbia County Public Health at (509) 382-218120 and City Hall at (509) 382-23612 before you count on either a septic system or a sewer tap.

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

We could not confirm a rule for living in an RV or a tiny home on a lot inside Dayton city limits. The city code defines recreational vehicles and RV parks, but we did not find the use rules that say where long-term RV occupancy is allowed. Ask City Hall at (509) 382-23612 before you park an RV on a city lot.

Columbia County's rule limiting RV occupancy on a residential property to 15 days in any six-month period covers unincorporated Columbia County only21; it is not the City of Dayton's rule. Washington defines a tiny house as a dwelling of no more than 400 square feet built to the state building code, with local approval for location22.

Manufactured homes are allowed in the AR zone through planned residential developments, manufactured home parks and manufactured home subdivisions23, and manufactured dwellings are a listed housing type in the UR zone24.

Can you add an accessory dwelling unit in Dayton?

Yes, with limits. Dayton's zoning code allows accessory dwelling units (ADUs) on residential lots, sized from 220 to 800 gross square feet6. A detached ADU may reach 25 feet to the roof peak, and it still has to meet the lot coverage, setback and height limits of the zoning table6.

Owners must register the ADU with the city planning department, and an occupancy permit is needed if the building code requires one6. ADUs are not permitted in cottage housing developments6.

How do you build a home in Dayton? The steps, in order

  1. Read the Title 11 zoning table for your district and the city's zoning map to confirm lot size, setbacks, height and coverage8.
  2. Call Columbia County Public Health at (509) 382-2181 about septic or the sewer connection and well questions20.
  3. Submit the building permit application to Columbia County Planning and Building, and take it to City Hall for planning review2.
  4. Pay permit fees when the permit is issued, not at submittal; the county keeps a fee schedule or gives estimates by phone25.
  5. Call (509) 382-3941 for building, mechanical or plumbing inspections and allow 24-hour notice26. Electrical permits and inspections run through the Washington State Department of Labor and Industries26.

What stays with Columbia County, and what to check before you buy in Dayton?

Land outside Dayton city limits falls under Columbia County's zoning and rules; see the Columbia County page for those answers. Septic and well review stay with Columbia County Public Health for any address3.

For planning, Columbia County's typical home value is $273,44627, and the effective property tax rate is 0.9 percent28. USDA rates only 7.3 percent of the county's soils as not limited for a conventional septic drain field, so expect a site evaluation and possibly an engineered system on land without sewer29. If the lot is near a creek, ask Columbia County Planning and Building about floodplain review before you design30.

Watch-outs

  • We could not confirm the city's rules for RVs, tiny homes, minimum house size or short-term rentals inside Dayton, so ask City Hall at (509) 382-2361 before you buy or build2.
  • The county's RV occupancy limit applies to unincorporated Columbia County, not to land inside Dayton city limits21.
  • Planning review happens at City Hall while building permits go to the county, so applications touch two offices2.
  • Permit exemptions for small structures come from the county's rules; confirm with Columbia County Planning and Building that a shed or small addition inside the city is exempt before you skip a permit16.

Sources

  1. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  2. City of Dayton City Hall (planning review) (daytonwa.com)
  3. Land Development, quoted and re-checked
  4. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  5. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  6. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  7. RCW 18.27.090 — Exemptions (Washington statewide rule), quoted and re-checked
  8. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  9. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  10. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  11. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  12. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  13. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  14. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  15. Columbia County Planning and Building (columbiaco.com)
  16. Frequently Asked Questions - Building and Planning, quoted and re-checked
  17. Land Development, quoted and re-checked
  18. WAC 246-272A-0200 Permit requirements (Washington statewide rule), quoted and re-checked
  19. WAC 246-272A-0025 — Connection to public sewer system (Washington statewide rule), quoted and re-checked
  20. Columbia County Public Health, Environmental Health (columbiacopublichealth.org)
  21. Chapter 18.95 Mobile Homes, Travel Trailers and Mobile Home Parks, quoted and re-checked
  22. Tiny Houses (Washington statewide rule), quoted and re-checked
  23. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  24. Dayton, WA Code of Ordinances, Title 11 Zoning Code (Municode) (Dayton), quoted and re-checked
  25. Building Permit Instructions, quoted and re-checked
  26. Building Information and Resources, quoted and re-checked
  27. Typical home value (Zillow): Bolthole Index county data
  28. Effective property tax rate: Bolthole Index county data
  29. 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
  30. Columbia County Zoning Ordinance, quoted and re-checked

Written October 24, 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 Dayton

Dayton’s own rules

  • Local zoningPresent

    Land inside Dayton city's corporate limits: the city adopts and administers its own zoning code (Title 11, Zoning Code).

    • The Title 11 zoning code applies to the territory within the corporate boundaries of the City of Dayton, per DMC 11-01.020.
    • Code is adopted under RCW 35A.63 and RCW 36.70A per DMC 11-01.010.
    “this title shall be known as the city of dayton zoning code.”
  • Zoning districtsPublished

    Land inside Dayton city limits: zoning districts are published in Title 11 (residential, commercial, industrial, and open space/public zones); an official zoning map is linked from the city site.

    • The city site links an official zoning map for the City of Dayton (PDF); the map itself was not opened in this research.
    “a. agricultural residential (ar). the intent of the agricultural residential zone is to retain a single-family, low-density residential character.”
  • Minimum lot sizeSpecified

    Agricultural residential (AR) zone inside Dayton city limits.

    • Infill exception under DMC 11-03.035 applies only where undeveloped lots exist between developed spaces within an existing residential zone: "a. lot area. minimum lot area for one detached dwelling unit shall be 2,500 square feet."
    • Cottage housing developments require a minimum lot area of 6,400 square feet under DMC 11-03.035.

    minimum lot area (AR zone): >= 10800 square feet (infill lots under DMC 11-03.035 may be 2,500 square feet for one detached dwelling)

    “lot area minimum 10,800 s.f. no min lot width minimum 80′ 50′”
    One more reviewed finding on this topic
  • SetbacksSpecified

    Agricultural residential (AR) zone, principal buildings, inside Dayton city limits.

    • Front and rear yard setbacks in AR are 20 feet; the table also lists side yard, corner-lot and through-lot setbacks not captured in this record (see followups).
    • Projection exceptions in DMC 11-03.030 allow cornices, eaves and similar features to project up to one foot into a required yard.

    minimum front and rear yard setback (principal building): >= 20 feet (corner and through-lot variations in DMC 11-03.030)

    “minimum front and rear yard setbacks for principal buildings including setbacks for front yards of a through lot 20′ 10′”
    One more reviewed finding on this topic
  • Lot coverageSpecified

    Agricultural residential (AR) zone inside Dayton city limits.

    • Impervious surface maximum is 65 percent in AR under the same DMC 11-03.030 table.
    • Accessory structures and residential tents count toward allowable building lot coverage.

    maximum building lot coverage: <= 40 percent (impervious surface maximum 65 percent)

    “lot coverage—maximum 40% 50% impervious surface—maximum 65% 65%”
    One more reviewed finding on this topic
  • Building heightSpecified

    Agricultural residential (AR) zone, principal buildings, inside Dayton city limits.

    • Within 10 to 20 feet of a property line the height limit is measured to the top of the wall plate: "buildings or structures more than 10 feet but less than 20 feet from a property line shall have a max. height from the finished grade to the top of the wall plate: 20′ hgt. 20′ hgt."
    • Height limits do not restrict water reservoirs, church spires and similar structures under DMC 11-03.030.

    maximum building height (roof): <= 35 feet (under the residential infill rules in DMC 11-03.035, ridges of pitched roofs at 4:12 or steeper may extend to 30 feet)

    “buildings, portions of buildings or structures shall have a max. height from the finished grade to the top of the roof: 35′ hgt. 35′ hgt.”
    One more reviewed finding on this topic
  • Manufactured homesAllowed (with conditions)

    Agricultural residential (AR) zone inside Dayton city limits: manufactured homes allowed through approved planned residential development, manufactured home parks and manufactured home subdivisions.

    • Varied housing types are allowed through approved planned residential development, manufactured home parks, and manufactured home subdivisions, per the AR zone intent.
    • A manufactured or mobile home park is defined as a parcel with a minimum of five mobile or manufactured homes under single ownership.
    • Manufactured home is defined as HUD-standard construction built off-site and transported to the site.
    “varied housing types may be allowed through approved planned residential development, manufactured home parks, and manufactured home subdivisions.”
    One more reviewed finding on this topic
    • Allowed (with conditions) — Urban residential (UR) zone inside Dayton city limits: manufactured dwellings are a listed housing type.
      “b. urban residential (dr). the intent of the urban residential zone is to provide for a mixture of housing unit types including single-family, duplex, manufactured and multifamily dwellings.”
  • Accessory dwellingsLimited

    Accessory dwelling units on residential lots inside Dayton city limits (zones where ADUs are permitted under Title 11 residential standards).

    • Designed to match or complement the principal structure's architecture.
    • Detached ADU may have a 25-foot exterior height to the roof peak, subject to the lot coverage, setback and height limits of DMC 11-03.030.
    • Apartments above garages or shops may be used as ADUs if zoning requirements, egress through the garage/shop bypass, and fire and building codes are met.
    • Owners must register the ADU with the city planning department; an occupancy permit must be obtained if required by building codes.
    • ADUs are not permitted in cottage housing developments (DMC 11-03.035).

    ADU gross floor area: 220 to 800 gross square feet

    “if detached from the primary residence, an exterior height of 25 feet to the top peak of the roof is allowed; providing, however, that all the other maximum lot coverage, setback and height limit limitations pursuant to dmc 11-03.030 are met.”

Still unanswered

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

  • Building permit — New residential construction inside Dayton city limits.
  • Owner-builder exemption — Owner-builder permit exemption inside Dayton city limits.
  • Inspections — Building inspections for new homes inside Dayton city limits.
  • Certificate of occupancy — Certificate of occupancy for new homes inside Dayton city limits.
  • Minimum dwelling size — Single-family dwellings inside Dayton city limits.
16 more unanswered
  • Living in an RV
  • Camping on your land
  • Tiny homes
  • Who permits septic
  • Septic permit
  • Septic inspection
  • Off-grid sanitation
  • Well permit
  • Mandatory utility hookup
  • Agricultural exemption
  • Subdividing land
  • Driveway access
  • Building in a floodplain
  • Short-term rentals
  • Permit fees
  • Permit process

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 Dayton publishes no rule on the point, not that none exists. Columbia County’s page lists the county offices to call.

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