Mason County, WA Building Setbacks & Zoning: Setback Rules (2026)

Mason County Code Section 17.04.213 governs lot dimensions in the Rural Residential 2.5 (RR 2.5) district, the county's base rural residential zone for parcels platted before December 5, 1996. Subsection (c) sets the front yard setback at a flat twenty-five feet. Subsection (d) sets the side and rear yard setback at twenty feet for the residential dwelling and its accessory buildings, but raises that to fifty feet for any accessory structure used for agricultural purposes or a home occupation. The same subsection carves out a narrower-lot exception: on a parcel with a lot width up to one hundred feet at the building site, the required side yard drops to ten percent of the lot width, though never below five feet from the property line.

Section 17.04.213(a) pairs these setbacks with a minimum lot size of two acres and a fifty-foot minimum lot width at any point. Identical setback numbers repeat at Section 17.04.223 for the RR 5 district and Section 17.04.233 for RR 10, so a twenty-five foot front yard and twenty-foot side and rear yard apply across the county's standard rural residential tiers. Section 17.04.217(e) allows the front, rear or side setback to be reduced further under the variance standards in Section 17.05.034. Building without meeting these setbacks is a violation of the development code enforced under Chapter 15.13, which authorizes civil fines and a stop-work order until the structure is brought into compliance or relocated.