Building permits, zoning and land rules in Columbia County, Washington

Yes. Columbia County requires a permit before the erection, movement, reconstruction, enlargement or alteration of a structure¹. The county has adopted building, residential, mechanical, fire and plumbing codes, including the 2021 residential standards and Washington amendments⁹.

The permit is only the start of compliance: issued permits identify which building, mechanical or plumbing inspections apply, and the county requests at least 24 hours' notice; call (509) 382-3941 to request a building, mechanical or plumbing inspection⁹. Electrical inspections are performed by the Washington State Department of Labor and Industries rather than the county⁹. The county publishes separate building and planning fee schedules, and online payments carry a minimum $2 or 2.5% convenience fee¹⁰.

Columbia County Planning and Building is the permit office for county building work and the office responsible for county land use and zoning². The office is at 115 E Main St. in Dayton and can be reached at (509) 382-4676². The department also provides building services for the City of Dayton, the towns of Waitsburg and Starbuck, and Garfield County, so identify the project jurisdiction when asking about a parcel².

Building applications may be submitted online or by email; emailed applications must be smaller than 20MB per email, and the county says it will confirm receipt within two business days¹¹. For a scoped fee estimate, use the county's published building and planning fee schedules or contact Planning and Building¹⁰.

Yes. Columbia County zoning regulates residential, commercial, industrial and agricultural development, while the City of Dayton has its own zoning ordinance¹. The parcel's zoning district matters because minimum lot size, setbacks, height and allowed uses are district-specific⁶.

For example, the A-2 minimum lot size is 5 acres and the A-3 minimum is 10 acres, while an AR-1 lot may require 7,200 square feet with public water and sewer or 1 acre where public sewer is unavailable⁶. A narrow A-1 exception can waive minimum lot size and dimensions for certain farm-unit divisions, but it carries agricultural, density and health conditions and may require conditional-use approval⁶. Ask Planning and Building to identify the controlling jurisdiction, district and dimensional table before designing a site plan^1,2.

Columbia County Public Health reviews and approves plans for septic systems and wells to meet health standards⁴. Public Health also reviews connections to public water and sewer, while separate right-of-way and city utility applications may apply⁴. The land-development materials provide a master on-site sewage disposal permit application and call for supporting items such as soil reports, water-quality tests and site plans⁴. State rules require a local-health-officer permit before installing, repairing, modifying, connecting to or expanding an on-site sewage system, except for a minor repair¹².

Only 7.3% of county soils are rated without severe limitations for a conventional septic drain field, so make septic feasibility an early purchase contingency rather than assuming a standard system will work¹³. For an existing system associated with a rural housing certificate or short plat, a licensed evaluator must assess current functionality, and a failing system must be repaired before further development⁴. A home expansion requires verification that the existing system can handle the added capacity, and a site evaluation is required for a property with no existing system⁴. Contact Environmental Health at (509) 382-2181 before commissioning a design¹⁴.

In unincorporated Columbia County, an RV may be occupied on a residential property or another approved location for no more than 15 days in any six-month period, with exceptions for construction use, an approved RV park, or other provisions of the zoning ordinance⁵. A tiny home that counts as a mobile home, travel trailer or RV under the county's zoning rules is treated as a permanent dwelling when used as a residence, and must meet the area rules for dwellings in its zone⁵.

Outside a mobile home park, a dwelling mobile home or travel trailer must carry a Washington factory-built-housing seal, have water and sewage service equal to conventional housing, sit on a permanent foundation specified by the county building official, and have permanent fire-resistant skirting⁵. A manufactured home cannot be placed or occupied without a siting permit from Planning and Building⁵. During construction, a temporary building permit with health-department approval, valid for six months or less, covers living on site, at a $5 fee⁵. In an approved conditional-use RV park, stays are generally limited to 30 days, with longer periods set in the park's use permit⁵.

Separately, RV parking or overnight facilities are a conditional use in the A-2 and A-3 agricultural zones⁶. Washington allows a tiny house of no more than 400 square feet built to the state building code, but local foundation, location and permit rules still apply⁷. Columbia County's minimum dwelling size could not be confirmed, so ask Planning and Building before ordering plans².

1. Ask Columbia County Planning and Building to confirm jurisdiction, zoning, allowed use, setbacks, height and lot standards for the parcel^1,6.
2. Have Public Health evaluate the water and wastewater path; prepare the septic materials or identify the public utility, city connection and right-of-way applications that apply⁴.
3. Secure permission before constructing an approach to a county road, or written Washington Department of Transportation permission for work on a state-highway right-of-way^15,16.
4. Submit the building application and project documents; the county offers online submission and confirms emailed applications within two business days¹¹.
5. Follow the inspection list printed on the issued permit, allow at least 24 hours for county inspections, and arrange electrical inspection with the state⁹.

Start with buildability, not the listing description. Confirm the parcel's zoning district, legal access, setbacks and whether a proposed division requires a short-plat or long-plat application^3,6. Check flood mapping and local review early because county rules restrict construction in floodplains or floodways in specified districts, and Washington requires a local floodplain development permit for development in a floodplain^10,17.

Treat wastewater as a major feasibility item because only 7.3% of county soils avoid severe conventional-drain-field limitations¹³. Public Health reviews well plans, but a universal private-well permit requirement could not be confirmed; ask Environmental Health what approvals and water-quality evidence apply to the parcel^4,14. Finally, budget around a 0.9% effective property-tax rate and a $2,215 median annual property-tax bill, recognizing that an individual parcel's assessment can differ¹³.