Kitsap County, WA ADU (accessory dwelling unit) Rules and Regulations (2026)

In Kitsap County, the single biggest factor in what ADU you can build is whether your property sits inside an Urban Growth Area (UGA) or outside one. The rules for size, owner-occupancy, parking, permits, and how many ADUs you can have all change at that line. So before you pick a model, the first question is where your parcel falls.

ADUs are allowed in most areas where a primary residence is allowed, but not in every zone. The notes below summarize Kitsap County Code 17.415.010 and 17.415.015 and the county’s February 2026 ADU brochure. The exact zone and constraints still depend on your address. For the statewide picture, see our Washington ADU laws guide.

County or city

These rules cover unincorporated Kitsap County. Bremerton, Port Orchard, Poulsbo, and Bainbridge Island each have their own ADU rules and permit counters. If the parcel is inside one of them, start with the city.

Inside a UGA vs. outside a UGA

Inside a UGA

• You may have up to two ADUs per lot, attached or detached.
• Size: the published urban code caps an ADU at 1,000 square feet, measured internally. It also provides a director-approved exception for an ADU occupying a whole floor of an existing residence. The former 60-percent comparison is no longer in the published urban standard.
• Location: the ADU has to be placed so it doesn’t prevent a future subdivision of the lot to meet the zone’s minimum density.
• Access: the lot uses the same entrance as the primary residence unless county code allows multiple access points for a single-family home.
• Sewer and water: the ADU must have an urban level of sanitary sewer service and comply with water regulations.
• Design and dimensions: the zone’s design standards, setbacks, height, and lot coverage apply.
• Conversions: an ADU built entirely within an existing structure doesn’t have to meet current setbacks or lot coverage if the footprint doesn’t grow.
• Alleys: a detached ADU doesn’t have to meet the setback from a public alley.
• Owner-occupancy is not a condition of the county’s urban ADU section.

Parking inside a UGA. A single ADU doesn’t need the additional off-street space if any one of these applies: the house already meets all its parking requirements, on-street parking is available, or the ADU is within one-half mile of a major transit stop as defined in state law. A second ADU needs one off-street space in addition to the house’s requirement.

Kitsap County’s periodic comprehensive plan update was due by December 31, 2024 under RCW 36.70A.130. State law also protects ADU development on qualifying UGA lots. Critical-area and watershed exclusions and parking exceptions mean the parcel still needs review; see RCW 36.70A.681.

Outside a UGA

Attached ADUs may be located in residential zones:

• One attached ADU per lot, within an owner-occupied primary residence.
• No more than 50 percent of the primary residence’s habitable area.
• Health district standards for water and sewage disposal apply.
• Additional off-street parking is required, with no additional street-side entrance.
• Not allowed where an ADU already exists.

Detached ADUs:

• One ADU per lot.
• The owner must live in either the primary residence or the ADU.
• No more than 50 percent of the house’s habitable area or 900 square feet, whichever is smaller, measured internally.
• Within 150 feet of the primary residence, or created by converting an existing detached structure such as a garage.
• Designed to maintain the appearance of the primary residence.
• All zone setbacks apply.
• Health district standards for water and sewage disposal apply.
• Mobile homes and recreational vehicles aren’t allowed as ADUs.
• Uses the same side-street entrance as the primary residence and provides additional off-street parking. Confirm the applicable parking schedule for the proposal.
• Not permitted on a lot that already has an attached ADU.

Attached vs. detached ADUs

Kitsap County treats the two ADU types differently, and the definition decides which size cap and permit path apply.

• An attached ADU is connected directly to the main home by at least four feet of habitable space. The county brochure notes a June 30, 2025 director’s interpretation: an enclosed breezeway at least four feet wide qualifies as the connection.
• A detached ADU is separate from the main home.

If a garage, shop, or storage space sits between the house and the unit, ask the county whether the connection qualifies before you design around the attached path on a rural lot.

ADU or guest house

A guest house is not an ADU. The county defines it as an accessory building for temporary guests, household staff, or the property’s occupants, and it isn’t a separate dwelling unit. Per the county brochure, a guest house:

• Must be under 900 square feet, with up to two habitable rooms.
• May have a kitchen or a bathroom, but not both.
• Can’t be rented separately, and only one is allowed per parcel.
• Isn’t allowed on a property with a detached ADU.
• Must be within 150 feet of the main home, share its street entrance, meet health standards, and have a county-approved notice recorded on title.

If you want a separate household with its own kitchen and bathroom, you’re describing an ADU.

Permits: construction permits, and sometimes a CUP

The county’s brochure lays out the path. In most urban areas, ADUs are a permitted use, so you need only construction permits. In rural areas, attached ADUs need only construction permits, but detached ADUs require a Conditional Use Permit in addition to construction permits (KCC 17.410). Budget time for that land use step before the building permit on a rural detached project.

Common submittal items include:

• A complete building permit application and fees.
• A site development plan.
• Scaled floor plans that clearly show the square footage of both the primary home and the ADU.
• Building elevations for new structures or exterior changes.
• Impact fees, if applicable.
• Utility documentation (water supply and sewer/septic capacity).

Existing unpermitted ADUs. Inside a UGA, an unpermitted ADU needs a permit under the county’s ADU and allowed-use provisions. Outside a UGA, the code has a separate approval path for an existing unpermitted ADU when, among other criteria, the current owner didn’t build it and didn’t own the property when it was built. If you bought a property with an unpermitted unit, raise it early.

Water, septic, and sewer

Utilities can be the real budget driver on a Kitsap ADU. The county’s submittal items include proof that your water supply is potable and has adequate flow, plus confirmation that sewer or septic can handle the additional demand.

Inside a UGA, the code requires an urban level of sanitary sewer service. Outside a UGA, the ADU must meet health district standards for water and sewage disposal. Water and wastewater capacity depend on the property and its utility systems. Confirm both before design begins.

Pre-approved plans

Kitsap County offers a pre-approved plan option in urban UGAs and in the cities of Bremerton, Bainbridge Island, Port Orchard, and Poulsbo, free when the plan is used unmodified. In rural unincorporated Kitsap, the plans are available for a fee, and the plan page notes that rural-zoned properties must also obtain Conditional Use Permit approval and pay a design fee. The county brochure ties the rural CUP to detached ADUs, so confirm which applies to your plan.

The current plan sets include Lille (480 square feet), Sidney (600), Sinclair (800), and Blakely (800, two-story), plus the Kitsap and Salish designs. The county lists approximate permit fees for each plan, excluding other fees that may apply. You can request a detailed plan set, watermarked “not for construction,” to review options and estimate costs.

The county lists permitted finish, roof, door, and window choices. Egress-window requirements still apply, and some interior-wall flexibility excludes the two-story plan. Confirm each proposed change against the selected plan set. These are county program plans; their approval does not establish approval of a Wolf model or its foundation on your parcel.

How a factory-built ADU fits

Wolf homes are modular, built to Washington’s residential code — not HUD (the federal standard for manufactured homes) manufactured homes, and not the mobile homes the rural code excludes. Washington L&I reviews the factory plans and oversees factory inspections, and each home carries its L&I insignia before shipping. Kitsap County still reviews zoning, the foundation, utility connections, and site inspections.

On a rural detached lot, the 900-square-foot and 50-percent caps are the numbers to test first; compare our models with both. Kitsap County sites are beyond the standard 20-mile delivery in Wolf’s published installation scope, and access varies widely from lot to lot, so transport and setting are quoted after the site review. See cost and the Washington ADU cost guide.

What Wolf checks first

For a Kitsap County project, we usually want to know:

1. Is the parcel inside a UGA or outside one? That answer changes the size cap, owner-occupancy rule, parking, the permit type, and how many ADUs are allowed.
2. What zoning applies at the address — and is it inside Bremerton, Port Orchard, Poulsbo, or Bainbridge Island instead?
3. Is there an existing lawful primary residence on the lot, and any existing ADU or guest house?
4. Can the water supply and the sewer or septic system handle the added demand?
5. Will the project need only construction permits, or a Conditional Use Permit first?
6. Does a smaller footprint or an attached layout avoid a constraint that a larger detached model would trigger?

We answer those before anyone talks about finishes. A backyard cottage that works on paper can still stall on utilities, occupancy rules, or the UGA boundary.

Get a free Wolf property evaluation: send us the address and how you plan to use the unit, and we’ll tell you what the parcel can support before you commit to a design.

This is general information, not legal advice. Confirm current rules, fees, and application requirements with Kitsap County or the city that has jurisdiction over your property.