Mason County, WA Building Setbacks & Zoning: Lot Coverage Limits (2026)

Section 17.11.150, 'Bulk and dimension standards,' lays out the R-1 district's development table as a list of standards and their values: density is capped at a max of 4 dwelling units per gross acre, and lot coverage is capped at 40% max lot coverage. The same table sets minimum lot area at 7,000 net square feet for a single-family detached home, 9,000 net square feet for a corner lot, and 11,000 net square feet for a duplex, plus lot frontage minimums ranging from 20 feet for flag lots to 70 feet for corner lots.

Building height in the R-1 district tops out at 35 feet for a primary structure (25 feet east of SR 3) and 20 feet for an accessory structure. The code allows the coverage and other bulk standards to be altered without a variance only through use of an overlay zone, PD regulations, or as a Master Development Plan, meaning an ordinary property owner cannot get an administrative exception to the 40 percent cap the way they can for some setbacks. The 40 percent figure applies specifically to the Allyn UGA's R-1 district; Mason County's other residential districts set their own coverage numbers in their own bulk tables, for example the Shelton UGA's Neighborhood Residential district caps building coverage at 35 percent and development coverage at 45 percent under Table 17.07.150.