Snohomish County, WA

Common application types

• Residential Building Permit
• Townhouse Permit
• Commercial Building Permit
• Land Disturbing Activities
• Administrative Conditional Use Permit (ACUP)
• Conditional Use Permit
• Boundary Line Adjustment
• Preliminary Subdivision
• Shoreline Permit
• Pre-application

New homes and additions

All residential projects require the Residential Building Application Checklist, a structural plan, a site plan, a drainage plan, and water and sewer approval from the Snohomish County Health Department. When drainage review is required it is handled through a separate Land Disturbing Activity (LDA) permit, and factors such as the amount of clearing, new impervious surface, slope and number of trees removed can trigger additional requirements. Critical Areas, Shoreline and Flood Hazard rules can add environmental review, projects needing SEPA review take additional time, and projects in a flood hazard area must submit surveyed existing ground elevations for the four corners of the site with the application. PDS also accepts pre-approved Registered Basic Plans from contractors.

ADUs and middle housing

In urban unincorporated areas the County follows HB 1337 and allows at least two ADUs per lot (two attached, two detached, or one of each); in rural areas one ADU is allowed per lot with a legally established single-family dwelling. The maximum ADU size is 1,200 square feet, and no additional off-street parking is required for ADUs in urban residential zones. HB 1110 applies to cities and does not apply to unincorporated areas, per the County's 2025 ADU briefing. Attached and detached ADUs are covered in Assistance Bulletins #13 and #12, and PDS publishes a Pre-Approved ADU Plan Catalog.

Decks, retaining walls and accessory structures

Uncovered decks 30 inches or less above ground and non-habitable structures under 400 square feet in rural zones or under 200 square feet in urban zones are exempt from a building permit, but must still meet property line distances and environmental regulations. Retaining walls for single-family residences and duplexes are covered by Assistance Bulletin #40. Assistance Bulletin #74 has the full exemption list.

Commercial tenant improvements and change of use

Tenant improvements are applied for as a Commercial Tenant Improvement permit through the PDS Permit Portal and normally receive a single-stage review, which PDS says normally takes up to 3 weeks, longer if corrections are required. Health Department review is also required when the lot is on septic or the business is a school or food-service operation. Work beyond the TI scope, such as structural changes, may require a Commercial Building Permit.

Land use review

Land use decisions are split by type: an Administrative Conditional Use Permit is decided by the department, a Conditional Use Permit by the hearing examiner, and variances either as Type 1 decisions by PDS or, for the Standard-Type 2 subtype, by the hearing examiner. PDS offers residential site review, commercial, land use and critical area pre-application meetings, and a pre-application meeting is required for Urban Center development applications with limited exceptions. A traffic pre-submittal conference (no fee) is required before applications that add trips to the road system, such as site plans, rezones, commercial building permits, plats and short plats, under SCC 30.66B.020.

Corrections and review

After all PDS reviewers finish, PDS issues a Review Completion Letter, often with plan mark-ups, and the applicant responds by uploading revised or additional documents to the portal. PDS notes that spring and summer applications typically take longer, and projects needing variances, critical area review, SEPA or drainage review take additional time.

Tips from SASHKOV

• Pay the intake invoice promptly: the application is not deemed complete or accepted until it is paid.
• Upload unlocked, legible files; screening checks that documents are complete, legible and unlocked.
• Respond to Health Department comments directly, since they typically send comments straight to the property owner.
• Issued permits are valid for 18 months and can be renewed once, before expiration, for another 18 months.

Where to apply

Permitting authority: Snohomish County Planning and Development Services (PDS). Online submittals: PDS Permit Portal.