Washington County, OR Accessory Structures: Shed & Carport Rules (2026)
Shed permit rules in Washington County, OR, also referred to as storage shed, backyard shed, or accessory building regulations, set size limits, setbacks, and when a building permit is required.
Key Facts
- Rear-yard coverage cap
- 25% of required rear yard
- Sq. ft. cap, lots to 12,000 sf
- 600 square feet total
- Setback trigger
- 120 sq ft or larger needs full zone setback
- Setback under 120 sq ft
- 3 feet from side/rear line
- Livestock structure setback
- 30 ft from line, 100 ft from home
Summary
Detached sheds and other residential accessory buildings in unincorporated Washington County can't cover more than 25% of a required rear yard, face a tiered total-square-footage cap based on lot size, and must meet full zoning setbacks once they reach 120 square feet.
430-1.1 Residential: A. Residential accessory uses and structures include, but are not limited to, the following: (1) Treehouses, playhouses and storage sheds greater than 120 square feet in area... B. Development Standards: Detached accessory buildings shall comply with the following, except as modified by other Sections of the Code: (1) Shall not occupy more than 25% of a required rear yard; (2) Within an urban growth boundary accessory buildings are subject to the following limitations on total square footage: (a) For lots up to 12,000 square feet - maximum of 600 square feet. (b) For lots larger than 12,000 square feet but less than 24,000 square feet - 5% of total lot area. (c) For lots larger than 24,000 square feet but less than 50,000 square feet - 5% of total lot area with no one building larger than 1,200 square feet... (3) Buildings less than 120 square feet shall be located at least 3 feet from the side or rear property line, except a street side yard...; (4) Buildings 120 square feet or larger shall meet the setback requirements of the underlying land use district...
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Community Development Code: Supplement 2 | Code of Ordinances: Supplement 25).
Full Breakdown
1 governs residential accessory structures, expressly naming "treehouses, playhouses and storage sheds greater than 120 square feet in area" alongside detached garages, greenhouses and similar buildings. B apply regardless of use: no detached accessory building can occupy more than 25% of a required rear yard, and within the urban growth boundary total accessory-building square footage is capped on a sliding scale: 600 square feet on lots up to 12,000 square feet, 5% of lot area on lots between 12,000 and 24,000 square feet, 5% of lot area (capped at 1,200 square feet per building) on lots between 24,000 and 50,000 square feet, and 2,500 square feet total (again capped at 1,200 square feet per building) on lots over 50,000 square feet.
Setbacks depend on size: a shed under 120 square feet needs only a 3-foot side or rear setback, while a shed of 120 square feet or larger must meet the full setback of the underlying zoning district. Buildings or structures for livestock or larger poultry housing must sit at least 30 feet from any property line and 100 feet from any existing residence other than the owner's. B(9) bars any variance or adjustment to that 20-foot detachment measurement.
Violations & Fines
The county will deny or condition a building permit where the property carries an existing, undisclosed Code violation under Section 215-2. Constructing an accessory shed that exceeds the rear-yard coverage, lot-size square footage cap, or required setback without approval is a Code violation prosecuted under Chapter 1.14 of the Washington County Code per Section 215-3.
Frequently Asked Questions
How big can my shed be before I need a full zoning setback in Washington County?
Is there a maximum total square footage for accessory buildings on my lot?
Can my shed cover most of my backyard?
Sources & Official References
Other rules in Washington County
How Washington County compares: Shed Permit Requirements by City·Compare Washington County to another location·View the Oregon accessory structures overview
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