Environmental Rules in Mason County, WA (2026)
5 rules for unincorporated Mason County, Washington.
Verified from official government sources
Stormwater Management
Unincorporated Mason County regulates stormwater under Chapter 14.48, adopting Ecology's Stormwater Management Manual for Western Washington and requiring erosion and drainage plans once new development crosses two thousand square feet of impervious surface for homes or five thousand square feet for commercial work, with civil penalties of fifty to one hundred dollars per site per day for violations.
Mason County Stormwater Runoff and Drainage Standards
Some RestrictionsMason County Code §§ 14.48.150(1), 14.48.220(1)
Development of individual, detached, single-family residences and duplexes exceeding two thousand square feet of impermeable surfacing must have a small parcel erosion and sediment control plan, and a residential site improvement plan (which includes a written description of the proposed work and development) prepared and submitted for county review and approval. Nonresidential development exce...
Erosion Control
In unincorporated Mason County, any new construction adding 2,000 square feet or more of impervious surface, or disturbing under an acre, must follow the small parcel erosion and sediment control standards in MCC 14.48.140. Builders must limit vehicle access to one stabilized route, keep bare soil covered, and file a small parcel erosion and sediment control plan with Community Development before grading begins.
Mason County WA Erosion & Sediment Control Rules
Some RestrictionsMason County Code § 14.48.140
The following new development shall be required to control erosion and sediment during construction, to permanently stabilize soil exposed during construction, to comply with small parcel requirements 1 through 4, to prepare a small parcel erosion and sediment control plan : ... (a) creation or addition of less than two thousand square feet of impervious surface area; (b) land disturbing activi...
Flood Zones
In unincorporated Mason County, no structure or land within a mapped special flood hazard area may be built, altered or filled without a development permit issued under Mason County Code Section 14.22.120. Community Development administers the permit, and Section 14.22.070 makes any noncompliance a misdemeanor punishable by up to $1,000 and 60 days in jail per violation.
Floodplain Development Permits in Mason County
Significant RestrictionsMason County Code §§ 14.22.060, 14.22.070, 14.22.120, 14.22.150
No structure or land shall hereafter be constructed, located, extended, converted, or altered without full compliance with the terms of this chapter and other applicable regulations. Violation of the provisions of this chapter by failure to comply with any of its requirements (including violations of conditions and safeguards established in connection with conditions) shall constitute a misdeme...
Boat Dock Permits
Mason County limits waterfront property owners to one dock per lot under its Shoreline Master Program, and caps single-use dock length at sixty feet from the ordinary high water mark on lakes and one hundred twenty feet on saltwater shorelines, under Mason County Code § 17.50.320; a dock built for a single-family home counts as an allowed water-dependent use.
Mason County Shoreline Dock Permit Standards
Some RestrictionsMason County Code § 17.50.320
(13)Docks should be allowed only for water-dependent uses or public access. A dock associated with a single-family residence is considered a water-dependent use. ... (B)If allowed under this program, no more than one dock may be permitted on a single waterfront lot. This does not apply to public recreational uses. ... a.Freshwater Dock. Measured from the waterward edge of the structure, the ove...
Flood Elevation Requirements
Mason County requires new and substantially improved residential structures in special flood hazard areas to elevate the lowest floor at least one foot above base flood elevation, the county's "flood protection elevation" defined in Section 14.22.040. Nonresidential buildings must meet the same one-foot freeboard or be floodproofed to that level, while critical facilities need three feet of freeboard under Section 14.22.170.
Base Flood Elevation Freeboard in Mason County
Some RestrictionsMason County Code §§ 14.22.040, 14.22.170
"Flood protection elevation" means one foot above the base flood elevation. ... New construction and substantial improvement ... of any residential structure shall have the lowest floor, including basement, elevated one foot or more above base flood elevation. ... New construction and substantial improvement of any commercial, industrial or other nonresidential structure, except those defined a...
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