Mason County, WA Zoning Overlays & Bonuses: Density Bonus Law (2026)

Mason County's density bonus for large-scale development is tied to its Master Development Plan (MDP) process, codified at MCC Chapter 17.70. An MDP is only available for a tract of at least ten acres inside an urban growth area, or two hundred fifty acres outside one, under MCC 17.70.011. Section 17.70.015(b)(2)(C) lets the Board of County Commissioners, or the hearing examiner for MDPs inside the Belfair urban growth area, approve a bonus above the number of dwelling units the underlying zoning district would otherwise allow, capped at the maximum residential density permitted anywhere in the Mason County Code.

In rural areas, an applicant can request a bonus up to the density that a performance subdivision would allow under MCC 17.03.032(a) and Chapter 16.21, and the county lets the applicant obtain that higher density through MDP approval alone, then subdivide by a standard subdivision rather than going through the separate performance subdivision process. Inside an urban growth area, the bonus is formulaic: one additional dwelling unit per gross acre for every five percent increase in the total minimum open space the project sets aside above what is otherwise required.

Before granting either bonus, the county must find that the project's design, through added privacy, open space, landscaping or amenities, offsets the impact of the added density, or that the higher density is compatible with existing uses nearby, and that no density is shifted from inside an urban growth area to land outside one. For parcels inside the Belfair mixed-use zone or the Allyn Village Commercial zone, MCC 17.70.012(2)(B) further requires the MDP to carry a residential density between three and fifteen units per acre.