ADU permit requirements across 16 Seattle-area cities
Side-by-side: which of Seattle, Bellevue, Kirkland, Redmond, Sammamish, Issaquah, Renton, Kent, Federal Way, Mercer Island, Shoreline, Tacoma, Lakewood, Puyallup, Everett, Lynnwood require a permit for an ADU, and what triggers one — each row quoted from the city's own code or permit page, with the source linked. Fees and review times appear where the city publishes them.
14 of 16 cities have authoritative rules on file · 16 always require a permit · 0 depend on the scope · 0 do not.
King County
| Jurisdiction | Permit? | Threshold | Fee | Review days | Source |
|---|---|---|---|---|---|
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Per Bellevue ADU reform (LUC Chapter 20.20.120): ADU size limits were increased from 800 sq ft to 1,200 sq ft or 40% of the structure, whichever is larger. Owner-occupancy is no longer required. Off-street parking: no parking is required for ADUs smaller than 1,000 sq ft, or for ADUs within 1/2 mile of frequent transit; 1 space for ADUs larger than 1,000 sq ft; for ADUs larger than 2,000 sq ft, 1 space on lots smaller than 6,000 sq ft and 2 spaces on lots larger than 6,000 sq ft. | — | 21–90 days | Cite verified 2026-08-04 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. An ADU may be up to 1,000 sq ft of floor area (and may not exceed the square footage of the primary dwelling), with up to two bedrooms, and may be up to 30 feet tall. ADUs are not permitted within required yard setbacks; a minimum 10-foot separation from other structures is required. Three off-street parking spaces are required for a property with an ADU, except within 1/4 mile of a major transit stop. | — | — | Cite verified 2026-05-29 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. IMC 18.500.090: ADU max 1,000 sq ft GFA excluding non-living areas (garage, storage sheds, decks) — except when the excluded area IS the location of the proposed ADU. Principal unit GFA must be ≥25% greater than largest ADU on the lot. Up to TWO ADUs per lot (any combination attached/detached) allowed alongside the primary residence. Owner- occupancy NOT required (preempted by WA HB 1337). New ADUs not subject to rear-yard setback when rear abuts a public alley (unless the city plows that alley). 4-ft walkway required from ROW/driveway to ADU primary entrance. Height per IMC 18.404 form-and-intensity for the underlying zone (typically 30 ft in SF-D / SF-S / SF-SL). Parking: one additional off-street stall required per Issaquah ADU site-plan rules (may be waived for ADUs within ½ mi of frequent transit per HB 1337). | Building permit fee is valuation-based (Issaquah adopts UBC Table 1-A bracket schedule). Plan review fee 65% of building fee. WA state BCC surcharge $6.50/unit. Application fees invoiced via https://mybuildingpermit.com; 3% credit-card service fee or pay by check / exact cash. Impact fees apply on top of permit fee: traffic concurrency, school, parks. HB 1337 caps ADU impact fees at 50% of single-family unit rate — confirm Issaquah's current adopted ADU schedule at fee schedule URL. King County sewer capacity charge (~$8k-$10k) applies separately if ADU is on the King County sewer system. | 45–120 days | Cite verified 2026-05-16 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Two ADUs per lot are allowed (one attached + one detached, two attached, or two detached) per KCC 15.08.350. A detached ADU shall not exceed 24 feet in height. One additional parking space is required per ADU unless within 1/2 mile of a major transit stop (KCC 15.05.040). Owner-occupancy is no longer required (HB 1337). | — | — | Cite verified 2026-05-29 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Up to two ADUs per lot, each either attached or detached. Maximum size 1,200 square feet. Owner-occupancy is not required for newly constructed ADUs (HB 1337 / RCW 36.70A.681). An ADU may be segregated in ownership from the primary dwelling, except in the Residential-L Shoreline Environment, and a DADU may be placed on its own unit lot through a unit lot subdivision. No off-street parking within one-half mile of a major transit stop; outside that, one space for the first ADU unless on-street parking is available within 600 feet or the property is within one-half mile of frequent transit. Must meet the development standards — floor area ratio, lot coverage, setbacks — that regulate the primary dwelling. Two ATTACHED ADUs need Building Code guidance from Planning and Building (425-587-3600). | — | — | Cite verified 2026-05-29 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. MICC 19.02.030 (interim regs implementing WA HB 1337, eff. 6/30/2024): ADU min 220 sqft GFA, max 1,000 sqft GFA AND capped at 25% of the parcel's allowed GFA (whichever is less). Up to 2 ADUs allowed per lot. Owner-occupancy NOT required (preempted by HB 1337). Setbacks: per underlying R-zone (front 20', side 5', rear 25' in R-9.6, etc.; see MICC 19.02.020(B)). Detached ADU may sit at a lot line if the lot line abuts a public alley. Parking: 1 stall/unit for lots <6,000 sf, 2 stalls/unit for lots ≥6,000 sf. Parking waived if parcel is within 1/2 mile WALKING DISTANCE of a light rail station (not generic "major transit"). Separate addressing assigned by City after Land Use approval. HB 1337 caps impact fees at 50% of SFR impact fees. | Phase A Land Use fee per MI Fee Schedule (Type II Land Use Review line). Phase B Building permit fee is valuation-based: ~$2,100 building + ~$1,365 plan review (65%) + WA BCC $6.50 + per-fixture plumbing/mech fees at $280k valuation. Impact fees (school, transportation, parks) ~$5,000-$15,000 BEFORE HB 1337's 50% ADU cap — confirm MI has updated its schedule. | 30–90 days | Cite verified 2026-05-16 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Redmond ADUs are governed by RZC 21.08.220. THE SIZE FIGURES BELOW ARE NOT CONFIRMED AS ADOPTED — confirm with Planning before relying on them. The document this rule was read from is a REDLINE OF PROPOSED AMENDMENTS, and it redlines both numbers: the detached-ADU cap reads "40 50 percent of the total square footage of the primary dwelling unit and the accessory dwelling unit combined, excluding any garage area" and "in no case shall it exceed 1,000 1,500 square feet" — 40% and 1,000 sq ft struck, 50% and 1,500 sq ft proposed. Detached ADU height 25 ft, or 28 ft within an accessory structure. One additional off-street space, waivable within 1/4 mile of a major transit stop. NOTE: owner-occupancy cannot be required — RCW 36.70A.681(1)(b) bars it — so any recorded covenant is a notice on title, not an occupancy condition. | — | — | Cite verified 2026-08-29 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Renton allows two accessory dwelling units (attached or detached) per legal lot (RMC 4-2-110A, Ord. 6160, 6-16-2025). Onsite owner-occupancy is not required and both units may be rented (HB 1337). Renton retained a 1,000 sq ft ADU maximum; ADU follows the residential-zone development standards (e.g., 5 ft side yard). The building plan-check fee is $0 for ADUs built through Renton's Permit-Ready ADU (PRADU) program. | — | — | Cite verified 2026-05-29 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Up to two ADUs per lot are allowed (with a detached single-family residence). A detached ADU can be a maximum of 1,000 square feet; an attached ADU can be up to 50% of the size of the single-family residence or 1,000 square feet, whichever is larger. Detached ADU height is capped at 24 ft. No additional parking is required if the property already has four or more spaces. Owner-occupancy is not required (HB 1337). | — | — | Cite verified 2026-05-29 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Max 2 ADUs per property. Pre-approved DADU plans via ADUniverse cut review to 2-6 weeks; custom designs follow standard plan submittal (SDCI Tips 103 + 106). OWNER-OCCUPANCY IS NOT REQUIRED and cannot be — RCW 36.70A.681(1)(b) bars a city from requiring the owner to occupy the ADU or another unit on the lot, so both units may be rented. A covenant recorded under the old rule can be released; SDCI publishes the Release of Owner Occupancy Covenant for ADUs form for exactly that. | — | — | Cite verified 2026-04-26 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Max ADU floor area: 1,200 sqft (SMC 20.40.210(C)) with shared-roof/separate-floor exception. Two ADUs per lot max (SMC 20.40.210(A)). Permit pathway: Building Permit required for both new construction and conversion-to-ADU. Garage-to-ADU conversion follows the Residential Additions checklist (per checklist scope statement) + ADU Worksheet. New detached ADU dwelling unit follows the Residential New Build checklist + ADU Worksheet. Reduced impact fees apply for ADUs (vs. primary dwelling). | Apply electronically via eTRAKiT (https://www.shorelinewa.gov/government/departments/planning-community-development/permit-center-remote-services/register-for-a-professional-etrakit-account). Impact fees apply at reduced ADU rates (Fire, Park, Transportation) — paid after permit review, before issuance. State Building Code Council surcharge $6.50. | 30–90 days | Cite verified 2026-05-17 |
Pierce County
| Jurisdiction | Permit? | Threshold | Fee | Review days | Source |
|---|---|---|---|---|---|
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. WA HB 1337 (signed 2023, code-adoption deadline mid-2025) requires cities ≥6,000 pop. to permit ≥2 ADUs per lot in SF residential zones, allow ADUs of ≥1,000 sq ft (state floor — cities may allow larger, e.g. Bellevue/Redmond/Sammamish 1,200), drop owner-occupancy requirements, and waive parking requirements within ½ mi of frequent transit. City adoption status varies; local size + design caps may exceed the state floor. | — | — | Cite verified 2026-04-29 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Permit required for any new detached accessory building >200sqft. Sheds/outbuildings ≤200sqft do not require a permit. | — | — | Cite verified 2026-04-29 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. Two ADUs per lot allowed (any lot size/width in residentially-zoned districts). Living area limited to 1,000 sqft (excluding non-living areas). Detached ADU setbacks: 5ft side property line (8ft if main entrance faces side), 15ft rear property line (no setback from alleys). Subject to standard zone height limits. | — | 21–60 days | Cite verified 2026-04-29 |
Snohomish County
| Jurisdiction | Permit? | Threshold | Fee | Review days | Source |
|---|---|---|---|---|---|
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. WA HB 1337 (signed 2023, code-adoption deadline mid-2025) requires cities ≥6,000 pop. to permit ≥2 ADUs per lot in SF residential zones, allow ADUs of ≥1,000 sq ft (state floor — cities may allow larger, e.g. Bellevue/Redmond/Sammamish 1,200), drop owner-occupancy requirements, and waive parking requirements within ½ mi of frequent transit. City adoption status varies; local size + design caps may exceed the state floor. | — | 30–90 days | Cite verified 2026-09-07 |
city | Always | An ADU or DADU always needs a building permit, and usually trade permits with it. WA HB 1337 (signed 2023, code-adoption deadline mid-2025) requires cities ≥6,000 pop. to permit ≥2 ADUs per lot in SF residential zones, allow ADUs of ≥1,000 sq ft (state floor — cities may allow larger, e.g. Bellevue/Redmond/Sammamish 1,200), drop owner-occupancy requirements, and waive parking requirements within ½ mi of frequent transit. City adoption status varies; local size + design caps may exceed the state floor. | — | — | Cite verified 2026-09-07 |
How this table is built
Each row reflects the most-recently-verified authoritative rule on file for that jurisdiction and project type. “Pending verification” means we have the jurisdiction in our database but haven't yet personally checked the city page for ADU rules — those rows fall back to county or WA-state baselines until verified. Sources link directly to the city or county page we read on the verified-on date. See our data-quality leaderboard for how we keep these current.