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

Franklin County's development standards set a hard percentage cap on how much of a lot may be built upon in its rural residential zones. 050(C), the RR-1 rural residential zone (one-acre minimum lot size, one dwelling unit per lot/parcel) limits maximum lot coverage to 40 percent. 050(C) sets maximum lot coverage at 40 percent on its five-acre minimum lots. 66 confirm that an open or enclosed porch counts as part of the building for lot coverage purposes, so covered porches and similar attached features reduce the buildable area left for other structures.

050), set minimum lot size, density, yard setbacks and height limits but do not carry a maximum lot coverage percentage in their development standards; on 20- and 40-acre agricultural parcels, the county relies on the large minimum lot size itself, rather than a coverage cap, to keep development proportionate. A homeowner or builder in RR-1 or RR-5 needs to check the 40 percent figure against total footprint, including attached porches, before finalizing a building permit application with the Planning and Building Department, since exceeding it is a zoning violation regardless of whether individual setbacks are otherwise met.