Building permits, zoning and septic rules in Lewis County, Washington

Yes. Lewis County requires an application to the Building Official and the required permit before covered building and development work in the unincorporated county begins¹. The application must include the parcel's legal description or tax parcel number, assigned street address, owner and contractor information, current contractor-registration verification, and required fees¹. Washington's state building code applies in every county and city, including residential construction in unincorporated Lewis County¹⁰. Lewis County publishes permit fees that vary by permit type, valuation, occupancy, plan review, inspection, and other project details; state, mechanical, and plumbing charges are not included in the building-permit fee⁸. Under the fee schedule effective January 1, 2025, the lowest building-permit fee is $30.85 for a valuation of $1 to $500, standard plan review is 65% of the base fee, and starting work without a permit costs double the permit fee⁸. An owner working on their own property may qualify for Washington's contractor-registration exemption when the work is not for sale, demolition, or lease, but that exemption does not remove building, electrical, plumbing, or other permits⁶.

Lewis County Community Development is the building, planning, zoning, and floodplain office for unincorporated Lewis County¹¹. The office is at 125 NW Chehalis Ave, Chehalis, WA 98532, and its permit-center phone number is 360-740-1146¹¹. Use SmartGov to submit an application, check permit status, or request an inspection¹¹. Master Site Review is the first development step and identifies county, state, and federal permits that may apply; after approval, applicants can pursue septic, fill-and-grade, building, and other permits². Inspection requests go through SmartGov only, and the daily cutoff is 6:30 a.m.; later requests move to the next day¹². The available county material does not establish one inspection sequence for every project, so ask Community Development which inspections apply to your permit.

Yes. Lewis County has an official zoning map for land under county jurisdiction, while incorporated municipalities may administer separate zoning rules⁴. Inside a city or town, ask that city's administrator, because its regulations may differ; in an unincorporated urban growth area, both county and city administrators may apply different parts of their codes¹³. Septic permits stay with Lewis County Environmental Health either way³. The county identifies its current official zoning map as effective October 1, 2025⁴. Ask Community Development to identify the parcel's district and allowed uses before designing a home, accessory dwelling, or short-term rental. County planning reviews proposals for both zoning and critical-area compliance². Road setbacks include 55 feet from the centerline where a county right-of-way is 60 feet wide or less, and 25 feet from the near edge where the right-of-way is wider than 60 feet¹. Other setbacks depend on zoning or the applicable building-code table¹. Minimum lot sizes for new subdivisions and segregations in the rural and resource districts run from 80 acres in Primary Forest Resource Land (with exceptions) and 20 acres in Local Forest Resource Land and Agricultural Resource Land, to 10 acres in Mineral Resource Land, and 20, 10 and 5 acres in the RDD-20, RDD-10 and RDD-5 rural development districts¹⁴. The RRC rural residential districts run from 10,000 square feet in RRC-A to 2 acres in RRC-E, and some other districts have no zoning minimum, so health code and available utilities decide lot size there¹⁴. In urban growth areas, residential minimums run from 2,500 square feet in RM to 7,500 square feet in AX¹⁵. Lewis County's available rules do not provide complete countywide answers for accessory dwellings outside the proposed urban-growth-area designations, lot coverage, or building height, so get those parcel-specific limits from Community Development.

Lewis County Environmental Health evaluates septic sites and test-pit soils, sets permit conditions, and issues on-site sewage permits³. New construction requires a sewage permit or evaluation application, a site project plan, and permission to enter⁵. Repair, replacement, alteration, connection, or reconnection can also require a permit; work outside the septic tank requires a permit, and tank replacement requires one⁵. A home or other building connecting to a permitted system installed more than one year before its building or mobile-home placement application needs a connection or reconnection permit⁵. A well that would serve more than one single-family residence needs a Lewis County Well Site Inspection Form, and Master Site Review approval comes before that application; an individual well is excluded from the form¹⁶. Request the construction final inspection through the county septic inspection line³. Only about 7.1% of Lewis County soils are rated without severe limits for a conventional drain field, so make septic feasibility an early check¹⁷. The county's available material does not confirm whether alternative off-grid sanitation systems are allowed; ask Environmental Health before planning one.

Lewis County's available rules do not confirm a general right to live long term in an RV on private property, a complete private-property camping rule, or a countywide tiny-home occupancy rule. The county's RV rules that we found cover RV parks and campgrounds, where the same party may occupy a camping site for no more than 210 consecutive days, and flood hazard zones, where an RV must stay fewer than 180 consecutive days, be fully licensed and ready for highway use, or meet the manufactured-home elevation and anchoring rules^18,19. Ask Community Development about the parcel's zoning, approved use, utilities, and permit path before buying an RV or tiny home for full-time occupancy⁴. Washington recognizes code-compliant tiny houses of no more than 400 square feet, including those built on wheels, but foundation, installation, location, and local permits still depend on the local building department²⁰. Lewis County defines a tiny home, also called an efficient dwelling unit, as a dwelling with living space, a bathroom and kitchen facilities and a total floor area of 220 to 1,000 square feet; that definition sets the size range, not a minimum for every dwelling²¹. Lewis County includes RVs, trailers, yurts, homes, accessory dwelling units, duplexes, detached bedrooms, and similar structures in its short-term-rental program²². Short-term rentals must register beginning January 1, 2026, with one calendar year to comply, and must have approved water, sewage treatment, onsite parking tied to bedroom count, and waste service or a secure receptacle²². Short-term-rental treatment does not establish permission for permanent occupancy.

1. Ask Community Development to confirm the parcel's zoning district, allowed use, critical areas, floodplain status, and setbacks^1,2,23.
2. Complete Master Site Review, the county's first development step; use Land Development Review for a subdivision or boundary-line adjustment².
3. Confirm the water and wastewater path; county-managed systems use availability forms, while wells, septic, municipal service, and other public systems can follow separate reviews².
4. Obtain the septic evaluation and permit from Environmental Health⁵.
5. Apply for a road approach permit if your driveway connects to a county road: the county lists $350 plus a $50 administrative fee, then checks ownership and legal access, and you call the Area Supervisor for final inspection after installing the approach⁹. A new private road or other new site access needs the appropriate application too².
6. Submit the building application and pay the applicable building, review, trade, and state charges^1,8.
7. Request building inspections through SmartGov and the septic construction final inspection through Environmental Health^3,12.

Confirm the zoning district and ask Community Development for the parcel's use, setback, critical-area, and floodplain constraints before relying on a seller's description^1,2,23. All development in a Lewis County floodplain requires a floodplain development permit, listed at $50 in the 2025 fee schedule, and an existing building is covered when improvements or repairs exceed 50% of its value, tracked cumulatively over 10 years^8,23. Confirm the actual water path because county-managed systems use availability forms, while wells, septic, municipal service, and other public systems can require different reviews². Order septic feasibility work early because only about 7.1% of Lewis County soils are rated without severe limits for a conventional drain field¹⁷. Verify legal access and whether a road-approach or private-road application is needed². If you intend to divide the land, start with Land Development Review: the county distinguishes long plats, short subdivisions, large-lot subdivisions, and simple segregations by lot count and acreage². Lewis County's median property tax bill is about $2,433 a year, with an effective rate near 0.7%¹⁷.