What happens if you skip the permit (and you needed one)
- Stop-work order issued by Kennewick Building Department and fines of $250–$500 per day of unpermitted work; remedial permit typically costs 1.5x the original permit fee ($6,000–$18,000).
- Title/resale disclosure: unpermitted ADU must be disclosed to future buyers; lenders often deny mortgages on properties with illegal ADUs, and sale price drops 10-20% on discovery.
- Insurance denial: homeowner's policy voids coverage for injury/damage in unpermitted ADU; renter's claim triggers insurer audit and potential policy cancellation.
- Neighbor complaint enforcement: Kennewick receives ADU complaints regularly; code enforcement can order removal of non-conforming structure, costing $15,000–$50,000+ in deconstruction.
Kennewick ADU permits — the key details
Washington State's Revised Code 36.70A.680 (in effect since January 1, 2023) mandates that all cities, including Kennewick, allow accessory dwelling units in all residential zones without owner-occupancy requirements or unreasonable parking restrictions. Kennewick's Building Department interprets this as blanket ADU eligibility: detached new construction on the same lot as a primary residence, attached ADUs (side-by-side or stacked), garage conversions, junior ADUs (interior additions without kitchen), and above-garage units all qualify. The city does not require you to owner-occupy the primary residence or the ADU itself, and you can legally rent both out — a major divergence from pre-2023 practice in Washington. However, state law does NOT eliminate setback, height, lot-coverage, or utility-capacity review; Kennewick still enforces IRC building standards (foundation, egress, fire-rated walls) and local utility infrastructure approval. Expect the Building Department to require a full site plan showing property lines, existing utilities (water/sewer/power), the proposed ADU footprint, setbacks from lot lines, and parking layout — even though parking is not a deal-breaker, showing it prevents delays.
Kennewick's climate and soils shape ADU-specific requirements. The city straddles two frost-depth zones: west of the Cascade foothills (toward Pasco), frost depth is 12 inches; east of the Columbia River, it climbs to 30+ inches. Your foundation design (slab-on-grade vs. stemwall vs. frost-protected shallow foundation) must match your lot's soil type and frost depth — this is where many projects get delayed during plan review. If you're in east Kennewick (Richland side), a 30-inch frost line means deeper footings or an FPSF (frost-protected shallow foundation) per IRC R403.3, adding cost and complexity. Kennewick's soils are predominantly glacial till (poor drainage, high bearing capacity) or volcanic loam (better); the city does not require geotechnical testing for typical residential ADUs under 2,000 sq ft, but if your lot is near the Columbia River floodplain or on fill, the Building Department may request soil and drainage verification — factor 4-8 weeks for that if triggered. Utility lines in Kennewick run at shallow depths (12-18 inches); ADU footings must avoid boring through existing sewer, water, or power. Hire a locating service (Dig Safe) before design finalization; one missed line can halt framing.
Separate utility connections are not mandatory per RCW 36.70A.680, but Kennewick's Building Department almost always requires a sub-meter for water and separate electrical service for an ADU that will be independently rented. The city's Water/Sewer Division (part of Kennewick Public Works) must approve any new tap or sub-metering arrangement; this adds 2-4 weeks and typically $2,000–$4,000 to project cost (meter box, service line trenching, permits from the water utility itself, separate from the building permit). If your ADU is within 10 feet of the primary residence and shares a water line with sub-metering, the Building Department approves this as a 'proportional share' arrangement — no second tap required. Electrical service is simpler: a sub-panel in the ADU counts as a separate service for code purposes; NEC 230.3 allows this without a second meter-main from the utility, though Kennewick Power (the local provider) charges ~$500–$800 for the secondary service review. Sewer is the hardest: if the primary residence is on a septic system (not city sewer), adding an ADU tenant may trigger Benton County Health Department rules requiring a second tank or system upgrade — inspect your health permit before committing to a septic-based ADU.
Plan review in Kennewick averages 6-8 weeks for a straightforward ADU (detached new construction on a regular lot, no wetlands, no flood zone). The Building Department uses a 'plan-check list' (available on their portal) that walks through IRC R310 (egress — every sleeping room must have a qualifying egress window or door), R401-R408 (foundation per frost depth and soil), Chapter 3 (fire and life safety — 1-hour fire-wall between ADU and primary residence if attached, or 5-foot fire-rated fence if detached and closer than 10 feet), and utilities. Most rejections stem from egress: a 12x20-foot bedroom with only one high window fails IRC R310.1 (minimum one exit per sleeping room + one emergency escape window per Code, or a separate entry door). If your ADU is a garage conversion with bedrooms, the door from the garage into the ADU must be tight-closing and self-closing per R310.3; a loose-fitting entry door means a resubmit. Kennewick's Building Department does not pre-approve generic ADU plans (unlike California or some Oregon cities), so expect iterative review: first submission, comments in week 3-4, redesign, resubmit, approval by week 6-8. Budget extra time if your site has complications: adjacent to a historic district overlay, in a floodplain, or on a lot smaller than 0.25 acres.
Inspections for an ADU in Kennewick follow the standard residential building sequence: foundation/footings (before concrete pour), framing (before wall sheathing), rough electrical/mechanical/plumbing (before drywall), insulation and drywall, and final. If the ADU is detached, fire-alarm or sprinkler requirements may trigger additional inspection points; Kennewick requires residential fire sprinklers in new residential construction over 5,000 sq ft (total for both primary and ADU), so a main house + 1,200 sq ft ADU on a single lot may cross the threshold and require sprinklers in both structures — add $8,000–$15,000 to project cost if this applies. Once the Building Department clears the final building inspection, the water utility inspects the meter/service line, the electrical utility inspects the secondary service panel, and the Planning Division signs off on setbacks and zoning compliance. Total inspection sequence: 2-3 months from framing-start to final sign-off. Owner-builders are allowed for owner-occupied ADUs in Washington; if you are the owner of the primary residence and will occupy the ADU yourself, you can pull the permit as an owner-builder (no contractor license required), saving 10-15% on plan-review fees. If you plan to rent the ADU to a tenant immediately, you may still qualify as owner-builder if you own the lot; verify with the Building Department before assuming.
Three Kennewick accessory dwelling unit (adu) scenarios
Washington State ADU law vs. Kennewick's local enforcement — where state law overrides city rules
Washington's Revised Code 36.70A.680, effective January 1, 2023, is a hard-cap state law that strips cities of authority over ADU zoning, owner-occupancy, and parking minimums. Kennewick cannot enforce a rule stating 'ADU allowed only if owner occupies primary residence' or 'maximum one ADU per lot' or 'ADU must be smaller than primary residence' — all of these are void. The law applies to all residential zones in Kennewick (single-family, multi-family, commercial-mixed-use). However, state law does NOT eliminate building code, setback, height, lot-coverage, utility-capacity, or fire-safety review. Many homeowners misunderstand this: they assume 'state law allows ADUs' means 'my ADU is automatically approved.' In fact, Kennewick's Building Department still requires full permitting, plan review, and inspections. The distinction: Kennewick cannot say 'no ADU on this lot because the owner doesn't occupy it'; but Kennewick CAN say 'your proposed ADU violates the 25-foot setback from the front lot line' or 'your septic system is under-capacity for an additional unit.' This is where local code enforcement still bites.
Kennewick's interpretation of RCW 36.70A.680 is cautious and building-code-focused. The city has NOT auto-approved pre-approved ADU plans (unlike California under SB 9, which allows state-approved plans to bypass local review entirely). Every ADU in Kennewick goes through the full plan-check sequence: site plan, utility plans, building plans, energy code, accessibility (ADA if applicable), and fire/life-safety. This means your timeline is 6-8 weeks minimum, not 2-3 weeks. The upside: Kennewick is not hostile to ADUs; the city has NOT imposed design overlays, height restrictions, or parking mandates that would effectively ban ADUs (as some Washington cities have tried to do, inviting legal challenges). The city's stance is: 'Allowed by state law; reviewed for code compliance; approved if code-compliant.' This is a fair baseline.
Owner-occupancy claims are a frequent point of confusion. RCW 36.70A.680 says cities cannot require owner-occupancy of the primary residence or ADU. But if you tell Kennewick Building Department in your permit application 'I will owner-occupy the primary residence,' you have NOT triggered a special 'owner-occupancy exemption' that speeds your permit. You still get the standard 6-8 week review. Some homeowners hope that claiming owner-occupancy exempts them from sprinkler requirements, fire-walls, or septic review — it does not. The state law waives the ZONING rule; it does not waive building-code rules. If your ADU + primary residence total 5,000+ sq ft on the lot, Kennewick still requires residential fire sprinklers under IRC R313 (section enforced statewide in Washington). Owner-occupancy does not exempt you.
Kennewick utility jurisdiction — City of Kennewick Water, Benton County Health, and permit complexity
Kennewick's utility landscape is fragmented, and this creates permit bottlenecks. The City of Kennewick Water Division (part of Public Works) operates the municipal water and sewer system within city limits; Benton County Health Department oversees septic systems, well water, and health-district-level utility approvals (even on lots within city limits, if the lot is septic). Kennewick Building Department cannot issue a final building permit without clearance from both. Many ADU applicants discover mid-permit that their septic system is undersized, or their well is non-potable, and the corrections add 4-8 weeks and $5,000–$15,000 to project cost. Hiring a septic/water engineer early (pre-permit, in the design phase) is essential. For city-sewer lots, the approval sequence is simpler: Kennewick Water reviews the utility plans (meter, service line, sub-metering), approves or asks for revision (1-2 weeks), then the Building Department can issue the building permit. For septic lots, Benton County Health must issue a septic-permit amendment before any ADU construction starts (4-6 weeks, $300–$500 fee, requires site visit and system design review).
Kennewick's Water Division has streamlined ADU utility approval via a form called the 'ADU Utility Verification Form' (available on the city's permit portal). The form asks: (1) Is the primary residence served by city water/sewer? (2) What is the proposed ADU utility strategy (new meter, sub-meter, shared meter)? (3) Does the existing water meter/sewer service have capacity for the ADU? Most standard lots (0.25 acres or larger) with existing 3/4-inch water meters have capacity for an ADU of 1,000-1,500 sq ft. If your lot is smaller or your meter is aged/undersized, the Water Division asks for an upgrade, which adds cost and timeline. The sewer side is less strict; City of Kennewick's wastewater-treatment plant has adequate capacity for most ADU additions. However, if your lot is on a septic system or a small municipal lagoon system (rural edge of Kennewick), sewer bottlenecks arise.
A critical detail for east-Kennewick (Richland/Benton border) ADUs: some lots are outside the City of Kennewick's utility service area and are served by the Town of Richland or Benton County Public Utility District #1. If you assume your property is in Kennewick (because your mailing address is 'Kennewick') but your water service is actually Richland or BPUD, your ADU permit must go through that utility's approval process, not Kennewick's. This causes 2-4 week delays when applicants file with Kennewick Building Department and later discover the utility jurisdiction mismatch. Solution: Call the City of Kennewick Permit Portal and verify your utility jurisdiction before design finalization. A simple 'Who provides my water/sewer?' call saves weeks of rework.
Kennewick City Hall, 210 W. 6th Ave, Kennewick, WA 99336 (verify mailing address for permit submission)
Phone: (509) 585-4200 — ask for Building Permits division; may route to Permits & Planning | https://www.ci.kennewick.wa.us/permits (or search 'Kennewick WA building permit online portal' if URL changes)
Monday-Friday, 8:00 AM - 5:00 PM (closed city holidays; verify holiday hours online)
Common questions
Does Washington State law really require Kennewick to allow my ADU, even if I don't owner-occupy the primary residence?
Yes. RCW 36.70A.680 (effective January 1, 2023) mandates that all Washington cities, including Kennewick, allow ADUs in all residential zones without requiring owner-occupancy of the primary residence or ADU. Kennewick cannot impose an 'owner must live in primary residence' rule. However, the city can still enforce building code, setbacks, utilities, and fire-safety requirements — those are separate from zoning. Your ADU is allowed by state law; it just must be code-compliant to be approved.
How long does the permit actually take from application to final sign-off?
Standard timeline for a straightforward ADU in Kennewick: 6-8 weeks for plan review, then 2-3 months of construction and inspections (foundation, framing, rough trades, final). Total from permit issuance to final certificate of occupancy: 4-5 months for detached/conversion ADUs, 5-6 months for attached additions. If your site has complications (septic review needed, structural engineering required, utility upgrades), add 4-8 weeks. Winter weather in Kennewick can delay construction inspections by 2-4 weeks.
Do I need a separate meter for the ADU water/sewer, or can I share the existing meter with the primary residence?
Kennewick prefers separate meters or sub-metering for independently rented ADUs (required by the Water Division if the ADU tenant pays their own utilities). If the ADU is rented to a tenant, a sub-meter or new meter box costs $1,500–$3,000 and requires Water Division approval (1-2 weeks). If the ADU is owner-occupied or family-occupied, sharing the primary residence's meter is allowed, though some landlords install a sub-meter anyway for utility-tracking. Sewer can be shared (proportional allocation); water meters typically need separation if tenants are billed separately.
My lot is on a septic system, not city sewer. Can I add an ADU?
Possibly, but septic capacity is the deciding factor. Benton County Health Department must review your septic system and determine if it has room for the additional occupants (an ADU tenant or family). A standard 1,000-gallon tank for a 3-bedroom primary residence is typically exhausted by a 2-bedroom ADU. You will either need a system upgrade (second tank, larger system, or advanced treatment like aerobic tank) or Health Department approval for a shared system. Expect 6-8 weeks and $5,000–$15,000 for system evaluation and possible upgrade. Contact Benton County Health Department before finalizing your ADU design.
Do I need a licensed contractor, or can I build the ADU myself as owner-builder?
Owner-builder is allowed in Washington for properties you own, including ADUs. If you own the primary residence and lot, you can pull the ADU building permit as an owner-builder (no contractor license required). However, some of the work (electrical, plumbing, mechanical) may still require licensed sub-trades depending on complexity. Verify with the Building Department whether your planned ADU type (detached, conversion, attached) allows full owner-builder construction or requires licensed trades for specific systems. Structural additions typically require a licensed contractor or engineer sign-off even if you own the property.
What happens if my ADU is too close to the property line — how close is allowed?
Kennewick's zoning code (KMC Chapter 14.02) sets setback requirements by residential zone: typically 5-25 feet from front lot line, 5-15 feet from side lot lines, and 5-10 feet from rear lot line (varies by zone). Detached ADUs must comply with these setbacks. If your lot is small (under 0.25 acres), a detached ADU may not fit within setback requirements, forcing a garage conversion or attached ADU instead. Pre-check setbacks before committing to a design. The Building Department's site-plan review (during permit processing) will catch any violations; no waiver of setbacks is available under state law.
Are fire sprinklers required in my new ADU in Kennewick?
Fire sprinklers are required if the combined square footage of the primary residence and ADU (on the same lot) exceeds 5,000 sq ft, per IRC R313 (adopted statewide in Washington). A 4,000-sq-ft primary residence + 1,200-sq-ft ADU = 5,200 sq ft total, triggering sprinkler requirement in BOTH structures. Sprinklers cost $8,000–$15,000 and add 2-3 weeks to design and plan review. If your ADU is under 1,000 sq ft and the primary residence is under 4,000 sq ft, sprinklers are typically not required. Confirm total square footage with the Building Department during pre-permit consultation.
Can I rent out both the primary residence and the ADU at the same time, or is there an occupancy limit?
Washington's state law (RCW 36.70A.680) eliminated owner-occupancy requirements, so you can rent both units to tenants. Kennewick does not impose a landlord-occupancy rule or a limit on how many ADUs or rentals you can have on a lot (though limited to one ADU per lot under state law; you cannot stack two ADUs on one parcel). Verify that you comply with Kennewick's short-term rental ordinance if you plan to use either unit as an Airbnb or vacation rental — those have separate licensing requirements.
What is the estimated total cost (permits + fees) for a typical ADU in Kennewick?
Building permit, plan review, and utility/impact fees combined typically total $4,000–$12,000 for an ADU in Kennewick, depending on size and complexity. Detached new construction (800-1,000 sq ft): $5,000–$7,000 in fees. Garage conversion: $3,000–$4,500. Attached second-story addition: $7,000–$12,000 (higher due to structural review). These are city fees only; construction costs are separate (typically $150–$250/sq ft, so $120,000–$250,000 for an 800-1,200-sq-ft ADU). Septic/utility upgrades, structural engineering, or utility meter changes add $2,000–$15,000 on top of city fees.
If my ADU plan is rejected during the first review, how much time and money does a resubmit cost?
A resubmit (second round of review) typically costs $800–$1,500 in plan-review fees and takes 3-4 weeks. Most first rejections are for egress violations (IRC R310), fire-separation walls, utility inadequacy, or setback non-compliance. Hiring a designer or contractor to coordinate the first submission (instead of filing a rough sketch yourself) usually prevents rejections and saves time and money overall. If the rejection is due to a fundamental site issue (undersized lot, septic failure, utility jurisdiction confusion), fixes may require 4-8 weeks and $5,000–$10,000.