8–14 weeks
UGA permit timeline
12–20 weeks
Rural permit timeline (with septic/well review)
This guide covers unincorporated King County (DPER) only. If your property is inside Bellevue, Renton, Kirkland, Redmond, Sammamish, or another incorporated city, that city's planning department handles permits — not DPER. Not sure? Our free feasibility study checks your jurisdiction automatically.
First: Determine Your Location
The permit process depends on whether your property is inside an Urban Growth Area (UGA) or in a rural area. This determines which rules apply, what infrastructure reviews are needed, and how long the process takes. For the full regulatory breakdown, see our King County ADU rules guide.
Urban Growth Area (UGA)
- R-zoned districts
- Usually on public sewer
- Faster DPER permit timeline
- ADUs generally allowed by right
Rural Area
- RA zoning — larger lots required
- Septic/well likely needed or upgraded
- King County Public Health review required
- Longer permit timeline
Not sure? Our free feasibility study checks automatically using GIS data.
DPER Permit Process
Zoning & Feasibility Review
- Confirm property is in unincorporated King County (not within Bellevue, Renton, Kirkland, or another city)
- Verify R or RA zoning district and lot size minimums
- Determine if property is inside an Urban Growth Area (UGA) or rural area
- Check for critical areas (wetlands, streams, steep slopes, habitats)
- Review setback and lot coverage requirements via King County's Parcel Viewer
Design & Engineering
- Prepare site plan with ADU placement and setback dimensions
- Create architectural drawings (floor plans, elevations)
- Complete structural engineering (if required)
- Prepare stormwater management plan
- Get site survey if property boundaries are unclear
Pre-Application Conference (Recommended)
- Schedule a pre-application conference with King County DPER
- Present preliminary plans and get written feedback
- Identify any site-specific requirements before formal submission
- Confirm utility, septic, and well requirements for your parcel
Submit Application
- Complete DPER permit application via King County's permit portal
- Submit all required documents and plans
- Pay application fees (building permit based on project valuation)
- Provide proof of water and sewer/septic capacity
DPER Review & Permit Issuance
- Planning division reviews for zoning and land use compliance
- Building division reviews structural, mechanical, and electrical plans
- Public Health reviews septic capacity (rural properties)
- Address any correction requests promptly
- Receive Standard Building Permit and begin construction
Additional Steps for Rural Properties
Rural King County properties have extra requirements beyond the standard DPER process:
Septic System Review
King County Public Health must review septic capacity. Existing systems may need upgrade or replacement ($15,000–$35,000 depending on system type). See our full permit cost breakdown for details.
Well Water Assessment
If on well water, ensure adequate capacity for an additional dwelling unit. May require a water rights review through the Washington Department of Ecology.
Critical Areas Assessment
Rural King County properties often have wetlands, streams, or steep slopes. A Critical Areas Ordinance (CAO) assessment by a qualified consultant may be required.
Road Access Review
Ensure the property has adequate road access for an additional dwelling. King County fire department access and driveway standards apply.
County permitting involves multiple departments. Our ADU permitting service coordinates with DPER Planning, Building, and King County Public Health on your behalf — your permit investment is applied as a build deposit when you sign the LOI. See our full cost breakdown for the complete investment picture.
King County Dept. of Permitting & Environmental Review (DPER)
Phone: (206) 296-6600
Website: kingcounty.gov/dper
Last updated: June 2026. Not legal advice. Verify current requirements with King County DPER.
Let Us Navigate County Permitting for You
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