Kennewick, WA Accessory Structures: ADU Permits (2026)

The two-track permitting process for a Kennewick ADU works as follows. Zoning Track: The applicant submits a zoning clearance application to the Kennewick Planning Division demonstrating compliance with KMC Title 18 standards as updated for HB 1337. Because RCW 36.70A.681 preempts conditional-use or discretionary review for compliant ADUs in areas zoned predominantly residential, the review is administrative/ministerial. Standards Kennewick may still impose include district-applicable setbacks (no more restrictive than the principal dwelling under HB 1337), height limits, and building-code-driven requirements. Building Track: After zoning clearance, the applicant submits construction documents under the Washington State Residential Code (WAC 51-51, adopting the 2021 IRC). Plan review confirms structural, electrical (NEC Article via WAC 51-54), plumbing (UPC via WAC 51-56), mechanical, energy (WAC 51-11R), and fire-safety provisions. Inspections occur at footing, foundation, framing, rough-in, insulation, and final stages. A Certificate of Occupancy is issued before the ADU may be occupied. The Local Project Review Act at RCW 36.70B.080 sets a 120-day standard processing time for project permits including ADUs, subject to applicant-caused tolling; RCW 36.70B.140 allows further streamlining of administrative permits. Kennewick may require separate utility connections or affidavits for ADUs with kitchens; water and sewer service is provided by the City of Kennewick Public Works.