Do I need a permit for an Accessory Dwelling Unit (ADU) in
Marysville, Washington?

Marysville ADU permits — the key details

Washington state law (RCW 36.70A.696, as amended in 2023) requires Marysville to allow at least one ADU per single-family lot, but does not strip the city of all local authority. Marysville Municipal Code Chapter 22.83 implements state law and requires that the primary residence on the lot be owner-occupied — a rule the state permits cities to enforce as long as it is not a de facto ban (Marysville's rule is not). The ADU itself does not have to be owner-occupied; you can live in the main house and rent the ADU long-term or short-term. However, if you sell the property before establishing owner-occupancy, the new owner must move in within 12 months or the ADU reverts to non-rental use (no tenancy allowed until owner-occupancy is re-established). This owner-occupancy requirement is enforceable via deed restriction and is flagged in the property record, so future buyers know the terms. Unlike state law in California (which allows junior ADUs and prohibits caps on ADU height in some cases) or Oregon (which mandates affordability pricing for some ADUs), Washington's 2023 amendments do not require affordability pricing in Marysville, nor do they mandate that you allow it — the city has chosen not to pursue affordability tiers. Your ADU can be any tenure (ownership, rental, vacation rental in some overlays).

Permit applications in Marysville require a site plan, grading and drainage plan, utility locations (water, sewer, power, gas if applicable), and a full set of architectural drawings if the ADU is detached or a conversion (garage-to-dwelling). If the ADU is attached to the primary residence (e.g., a junior ADU sharing a wall), the drawings can be simpler, but you still need to show the separate entrance, separate metering for utilities, and proof that the combined lot coverage (main house plus ADU) does not exceed Marysville's limits (typically 40% lot coverage in single-family zones). The City of Marysville Building Department (located in the Community Development Department, 1220 3rd Ave SE, Marysville, WA 98270) requires a pre-application meeting for most ADUs to vet setbacks and lot-size compliance. This pre-app ($350–$500) is not mandatory but highly recommended — it often reveals killer issues (e.g., easement conflicts, required tree preservation) before you spend $5,000 on design. The permit application itself (Marysville form ADU-1 or similar, available on the city's website) must be filed with the site plan, architectural set, and proof of property ownership or authorization. Owner-builders are allowed for owner-occupied ADUs (per RCW 19.27.095) but must obtain an Owner-Builder Permit (an additional step, $100–$200) before pulling the main building permit. The city does not accept applications via email; all submittals must be made in person at the permit window or via the city's online portal (verify current URL with the city's website, as portals shift).

Setback and lot-size rules in Marysville are stricter than state minimums and are enforced strictly. A detached ADU must be set back 5 feet from side property lines (not 0 feet, as some WA cities allow), 10 feet from rear property lines, and 15 feet from the front property line (measured from the right-of-way). The minimum lot size for a detached ADU is 4,000 square feet; if your lot is smaller, you can pursue a junior ADU (attached or above-garage) with a lower floor-area ratio (FAR) or footprint. A junior ADU (defined as a self-contained unit within or attached to the primary residence, typically 500 sq ft or less, with its own entrance and utilities) is permitted on any lot size, but may not exceed 50% of the primary residence's floor area or 800 square feet, whichever is smaller. An above-garage ADU (detached structure above a parking structure) can be up to 1,000 square feet and is treated as detached for setback purposes. Maximum ADU floor area in Marysville is 1,200 square feet for a detached unit or 800 square feet for a junior ADU, though the state has moved toward eliminating caps; check current city code (as of 2024, Marysville's caps are still in force). If your lot is in the downtown urban village overlay (roughly the core of historic Marysville along 3rd Ave and State St), setbacks are reduced to 0 feet from side lines and 5 feet from rear, and minimum lot size is waived — this is a major incentive for ADU development in Marysville's walkable core. Parking is required (one space) unless the ADU is in the urban village overlay, lacks a garage, or is within a quarter-mile of a transit stop (Marysville Transit operates bus service, but transit proximity is narrowly construed). If parking cannot fit on-site, Marysville requires a parking-in-lieu fee ($10,000–$15,000 per space as of 2024) or a shared parking agreement with an adjacent property.

Utilities and infrastructure are a frequent source of delays in ADU permits. Marysville's water and sewer systems are managed by the Public Works Department, and the Building Department cannot sign off until utilities verify capacity and approve meter locations (separate meters or sub-metering is required for the ADU; you cannot share a single meter). If your lot is on a septic system (common in unincorporated Snohomish County but less common in city of Marysville), the ADU must have its own system or tie into the primary residence's system with a separate compartment, and you'll need an on-site sewage system design approval from the Snohomish Health District (a separate permit, $300–$500, 4–6 weeks). If the lot is served by the city sewer, Marysville may require you to demonstrate that the existing lateral (pipe from house to main) has capacity for an additional dwelling unit; if not, upsizing is on your dime ($2,000–$5,000). Electrical, gas, and telephone connections must be shown on the utility plan, with the ADU meter or service entrance located separately from the primary residence (or clearly demarcated if combined on a common pedestal). If you're planning geothermal or solar for the ADU, those systems require additional electrical permits (included in the ADU permit fee but reviewed separately by the city's electrical inspector). Drainage is critical in Marysville's marine clay and glacial-till soils; the city requires a geotechnical report if the lot is on a slope steeper than 10% or if the ADU is within 50 feet of a mapped drainage channel. This report ($800–$2,000) is often a surprise cost and can delay permitting by 2–4 weeks if the report recommends special foundations or drainage mitigation.

Timeline and fees are best understood as a sequence: Pre-application meeting (if pursued), 1–2 weeks, $350–$500. Permit application and plan review, 6–10 weeks, $800–$1,500 (base permit fee, typically 1% of project valuation, capped at $10,000 per Marysville's fee ordinance). Plan-review re-submittals (common for setback or utility clarifications), 2–4 weeks per round, no additional fee if minor (one round of corrections is typically included). Utility approvals (water/sewer), 2–4 weeks, no direct fee to applicant (processing fee absorbed in permit fee). Permits ready for issuance, 1–2 weeks. Building, 8–16 weeks on-site (depends on scope: detached is longer than junior ADU conversion). Inspections (foundation, framing, electrical, plumbing, final), 4–8 weeks overlaid with construction. Certificate of Occupancy issued, 1–2 weeks after final inspection. Total wall-clock time from first inquiry to occupancy: 6–8 months for a straightforward junior ADU, 8–12 months for a detached unit if site conditions are clean. Permit fees in Marysville are structured as follows: Base building permit (1% of valuation, capped at $1,500), $800–$1,500. Plan-review deposit, $500–$1,000. Utility permits (water, sewer, electrical), included in base permit. Engineering review (if required for drainage or geotechnical), $300–$600. Total permit fees: $1,600–$3,600. Add impact fees if applicable: School impact fee (if the ADU adds residential density), $2,000–$4,000. Parks/recreation impact fee, $500–$1,000. Traffic impact fee (rare for single ADU), $200–$500. Total cost of permits and fees: $4,300–$9,100. Design, engineering, and construction costs are separate and typically total $80,000–$200,000 for a 600-sq-ft detached ADU (depending on materials, site work, and labor market in 2024–2025).

Three Marysville accessory dwelling unit (adu) scenarios

Why Marysville's owner-occupancy rule survives state preemption — and what it means for your rental plans

Washington's 2023 ADU law (RCW 36.70A.696) explicitly authorizes cities to require owner-occupancy of the primary residence — it does not override this rule. The statute reads: 'A city or county may require that the owner of the property where the accessory dwelling unit is located reside in either the principal residence or the accessory dwelling unit.' Marysville chose to require that the owner reside in the primary residence specifically (not the ADU), which is a narrower rule than some cities allow. This rule is enforceable by deed restriction and is checked at the time of permit issuance; the city requires the homeowner to sign a covenant restricting the primary residence to owner-occupancy. If you violate the covenant (you move out and rent both the primary home and the ADU), the city can issue a notice of violation ($250–$500 penalty per day of violation) and ultimately force the ADU to be shuttered (no tenancy) until the owner re-occupies the primary residence. However, once you establish owner-occupancy and rent the ADU, you can maintain that rental tenancy indefinitely — the rule does not require you to re-occupy the primary residence each year. The practical catch: If you sell the property, the new owner must move into the primary residence within 12 months of purchase, or the ADU tenancy automatically terminates. This is disclosed via title and recorded deed restriction, so any buyer and their lender will know the constraint upfront. For investors, this means Marysville ADUs are less attractive for portfolio acquisition (you cannot buy multiple ADU properties and collect rents on both the ADU and the primary residence). For owner-occupants who plan to rent the ADU and stay in the main house long-term, the rule is transparent and not a practical barrier. The state law does NOT require affordability pricing, inclusionary zoning, or rent caps — Marysville does not impose them either, so your ADU rental rate is market-driven.

Marysville's impact-fee exemption in the urban village overlay — and how it affects your site-cost math

Marysville's downtown urban village overlay (roughly 3rd Ave S to 4th Ave S, State St to Everett Ave, plus infill blocks) was updated in 2022 to exempt ADUs under 750 square feet from school, parks, and traffic impact fees. The city council's reasoning was to incentivize infill housing in the walkable core where infrastructure is already built out and parking is constrained. For a junior ADU (600–750 sq ft) in the urban village, you owe $0 impact fees; a detached ADU over 750 sq ft (e.g., 800 sq ft) still owes school impact fees ($2,800–$3,200), but parks and traffic fees are waived. Outside the urban village (standard residential zones), all ADUs over 600 sq ft owe impact fees: school ($2,800–$3,200), parks ($600–$800), traffic (rare, $100–$300). This exemption is meaningful — it saves $3,400–$4,000 per project and incentivizes ADU development where the city wants it (downtown infill rather than sprawl on the edges). If you're comparing sites, the urban village ADU will be $3,400 cheaper in soft costs, which can shift the ROI on a rental project. The exemption applies at the time of permit issuance (2024), but it is a city ordinance, not state law, so it could be repealed or modified if the city council votes to change it; most cities do not repeal impact-fee exemptions, so this is low risk.

Common questions