Environmental Rules in Cowlitz County, WA (2026)
6 rules for unincorporated Cowlitz County, Washington.
Verified from official government sources
Stormwater Management
New development in the unincorporated, non-urbanized area of Cowlitz County that adds 12,000 square feet or more of impervious surface, equal to at least 15 percent of the parcel, must control stormwater runoff under CCC Chapter 16.20, with violations enforceable as a civil infraction.
Rural Stormwater Development Rule, Cowlitz County
Some RestrictionsCowlitz County Code §§ 16.20.010, 16.20.030, 16.20.100
Ensure that property owners control the volume and rate of stormwater runoff originating from their property so that adjacent and downstream property and property owners' rights are protected, soil erosion minimized, off-site sedimentation prevented and flooding potential reduced; ... The provisions of this chapter shall apply to development that: ... Creates an additional 12,000 square feet or...
Erosion Control
Anyone grading land in unincorporated Cowlitz County must install erosion control structures before work starts and keep them in place until vegetation is established, under Cowlitz County Code § 16.35.080(A). No sediment from a grading site may leave the property or reach surface waters or wetlands, enforced by the Department of Building and Planning.
Cowlitz County Erosion Control During Grading
Some RestrictionsCowlitz County Code § 16.35.080(A)
§ 16.35.080. Grading standards. ... A. Appropriate erosion control structures shall be installed prior to any grading activity. All erosion control measures shall be maintained in place until vegetation is established for suitable erosion and sedimentation control. No sediment from grading operations shall be permitted to leave the site or enter any surface waters or wetlands.
Flood Zones
In unincorporated Cowlitz County, any construction or development within a mapped special flood hazard area needs a floodplain permit before work begins, per Cowlitz County Code Chapter 16.25. New buildings and manufactured homes must be anchored against flotation and built with flood-resistant materials, and large subdivisions must supply base flood elevation data before approval.
Cowlitz County Floodplain Development Standards
Some RestrictionsCowlitz County Code § 16.25.080(A)
A. General Standards. ... In all areas of special flood hazard, the following standards are required: ... All new construction and substantial improvements, including those related to manufactured homes, shall be anchored to prevent flotation, collapse, or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads including the effects of buoyancy. ... Where subdivision...
Defensible Space
Property owners in unincorporated Cowlitz County who use defensible space to satisfy fire-flow requirements must clear 30, 50 or 100 feet around structures under Fire Code Table B105.1(3), then record a maintenance covenant with the County Auditor and certify upkeep annually under WUI Code Sections 604.5 and 604.6.
Cowlitz County Defensible Space Requirements
Some RestrictionsCowlitz County Code §§ 16.05.080 Table B105.1(3), 16.05.090.P-Q (IWUIC §§ 604.5-604.6)
TABLE B105.1(3) Method Credit/Reduction ... 5 Provision of Defensible Space per site Wildland-Urban Interface Area classification (IWUIC). Minimum 30 ft. 500 gallon per minute fire flow credit 6 Provision of additional Defensible Space per Wildland-Urban Interface Area classification. (IWUIC). Minimum 50 ft. 250 gallon per minute fire flow credit 7 Provision of additional Defensible Space per W...
Vehicle Idling Restrictions
In unincorporated Cowlitz County, CCC § 10.25.040(B)(4) makes it a public noise disturbance to idle a stationary truck weighing more than 10,000 pounds GVWR for over 10 minutes at night in a rural, residential area, unless the vehicle is doing emergency or public utility work exempted under § 10.25.050.
Cowlitz County Truck Idling Time Limit
Some RestrictionsCowlitz County Code § 10.25.040(B)(4)
The operation or idling, for more than 10 minutes at a time, of stationary trucks weighing in excess of 10,000 pounds GVWR, except vehicles engaged in emergency or public utility work exempted under CCC § 10.25.050.
Flood Elevation Requirements
New and substantially improved buildings in unincorporated Cowlitz County's mapped flood zones must sit above the base flood elevation, not just at it. Cowlitz County Code § 16.25.080(B) requires one foot of freeboard for residential lowest floors and two feet for commercial and industrial buildings, plus elevated or floodproofed mechanical equipment.
Cowlitz County Flood Elevation Freeboard Rule
Some RestrictionsCowlitz County Code § 16.25.080(B)
In AE and A1-30 zones or other A zoned areas where the BFE has been determined or can be reasonably obtained, new construction and substantial improvement of any residential structure shall have the lowest floor, including basement, and all machinery, utilities and mechanical equipment elevated one foot or more above the BFE. ... New construction and substantial improvement of any ... commercia...
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