Environmental Rules in Lewis County, WA (2026)
4 rules for unincorporated Lewis County, Washington.
Verified from official government sources
Stormwater Management
Development in unincorporated Lewis County that adds 5,000 square feet or more of impervious surface, or any subdivision, needs Storm Drainage Approval under LCC § 15.45.090 before a building or subdivision permit can issue. The Public Works Administrator reviews plans stamped by a licensed civil engineer, and small single-family lots under set impervious-surface thresholds are exempt.
Lewis County Stormwater Management Requirements
Some RestrictionsLewis County Code §§ 15.45.030, 15.45.090(3), 15.45.100(5)
The provisions of this Chapter shall apply to all site development activities requiring building, mobile home placement or flood damage prevention reviews and/or permit approvals under Title 15 LCC and to subdivisions approved under Title 16 LCC, within the bounds of unincorporated Lewis County. No site development activities requiring said Titles 15 or 16 LCC reviews or approvals shall be init...
Erosion Control
In unincorporated Lewis County, construction adding 5,000 square feet or more of new impervious surface must obtain a Storm Drainage Approval under LCC Chapter 15.45 and include erosion and sedimentation control best management practices. LCC § 15.45.310 defines those BMPs as measures that trap sediment, curb off-site vehicle tracking, and stabilize exposed soil; LCC § 15.45.500 makes noncompliance a public nuisance subject to a stop work order.
Lewis County Erosion and Sediment Control Rules
Some RestrictionsLewis County Code §§ 15.45.090, 15.45.310, 15.45.500
(3) All construction, including remodeling, reconstruction, and new construction which add five thousand (5,000) square feet or more of impervious surfaces, including gravel parking areas. ... Erosion and sedimentation control ... BMPs are designed to prevent, minimize, or capture sediments and pollutants released during construction or under post project conditions. Some of these BMP's may be ...
Flood Zones
Any construction or development within a special flood hazard area of unincorporated Lewis County needs a flood hazard zone permit before work begins, under LCC § 15.35.140. The area is defined by the county's 1981 Flood Insurance Study and FIRM maps, as amended, and the county building official administers the permit, reviewing site plans, elevations, and floodway impacts before approval.
Lewis County Floodplain Development Permit Rules
Significant RestrictionsLewis County Code §§ 15.35.050, 15.35.140, 15.35.180(2)
This chapter shall apply to all areas subject to a base flood and/or designated as an area of special flood hazard within the jurisdiction of Lewis County. ... A development permit entitled flood hazard zone permit shall be obtained before construction or development begins within any area of special flood hazard established in LCC § 15.35.060. The permit shall be for all structures including m...
Flood Elevation Requirements
In unincorporated Lewis County's special flood hazard areas, new construction and substantial improvements must be elevated to the flood protection elevation, which LCC § 15.35.260 sets at the base flood elevation plus two feet of freeboard. Residential structures must raise the lowest floor, including any basement, to that height, while nonresidential buildings may floodproof to the same level instead.
Lewis County Base Flood Elevation Freeboard Rule
Some RestrictionsLewis County Code §§ 15.35.040, 15.35.260, 15.35.270(1)
"Freeboard" means an additional height requirement above the base flood elevation (BFE) that provides a margin of safety against extraordinary or unknown risks. This protects structures from waves, debris or unpredictable hazards that accompany the base flood. ... In order to account for the impacts of future development on flood depths, and in order to ensure the least expensive insurance rate...
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