ADU Regulations in Snohomish County: Jurisdiction and Parcel Checklist

By NW General Contractor. Updated October 11, 2026 after a substantive scope and source review.

Start with the property, not a statewide headline

An ADU is a separate dwelling on a property with a principal home. Whether you can build, convert or enlarge one depends on jurisdiction, zoning, site conditions and the proposed design. This guide helps you prepare a parcel review; it does not establish development approval.

Start with the parcel jurisdiction. An Everett mailing address does not establish that the property is inside city limits. Use Everett Permit Services for city property and county residential permit guidance for unincorporated Snohomish County. Ask which building, plumbing, mechanical, electrical or site-work approvals apply to the actual scope. A building-permit exemption does not waive other applicable requirements.

What the state framework actually says

Under RCW 36.70A.681, qualifying single-family lots within an urban growth area must generally allow at least two ADUs. The listed configurations include two attached units, two detached units, or one of each. That is not a promise that every parcel can physically accommodate the same development.

RCW 36.70A.680 addresses local implementation and limits the relevant ordinances to urban-growth-area portions of jurisdictions. Rural property needs its own county review; do not apply an urban summary to it.

Parking is conditional, not universally eliminated

The state law limits local off-street parking requirements. It prohibits such a requirement within one-half mile walking distance of a major transit stop; elsewhere it sets limits linked to lot size and contains exceptions. Confirm the local rule, walking-distance measurement and any exception for your parcel. Do not remove existing parking or finalize a site plan from this summary.

A practical ADU feasibility checklist

• Confirm city limits, zoning, urban or rural status and the legal lot.
• Identify the proposed unit type, existing dwellings and existing accessory buildings. A garage conversion still needs a habitable-space assessment.
• Map utilities, sewer or septic capacity, drainage, access, easements and areas where construction is restricted.
• Check critical areas and buffers before placing a footprint. State ADU provisions do not override every environmental or public-health restriction.
• Ask the jurisdiction about current size, height, setbacks, lot coverage and applicable parking rules.
• Request a scope-specific list of plans, approvals, inspections and fees.

Pre-approved plans do not approve the parcel

Snohomish County lists a pre-approved ADU plans rule adopted February 2, 2026, in its PDS rules. Everett also links a pre-approved designs program from Permit Services. Ask whether a plan fits your jurisdiction, site and intended changes, and what site-specific documents and engineering remain necessary.

Move from feasibility to a budget

Compare conversion and new-construction scopes only after checking the existing structure and utility work. Use the ADU budget checklist to identify missing costs, then discuss ADU construction with the address and intended use. Rental income, resale value and permit timing are not guaranteed by an ADU entitlement.

Sources and next checks

Source pages reviewed October 11, 2026. Confirm the current requirements for your address and proposed work before committing to a design or start date.

• City of Everett Permit Services
• Snohomish County residential permits
• RCW 36.70A.680: local regulation
• RCW 36.70A.681: limitations on local regulation
• County PDS rules

Discuss your project

Request a free estimate with the property address, priorities and available records.

Call (425) 439-7700