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Kitsap County ADU Rules: What Homeowners Need to Know (2026)

ByKristel Daugherty

An accessory dwelling unit — a backyard cottage, a garage conversion, or an apartment inside your home — is one of the most common things people ask me about right now. Some want room for aging parents, some want rental income, and investors want to know whether the numbers work. Almost everyone starts with the floor plan. That’s the fun part, but it’s not where the project gets decided.

Kitsap County ADU rules turn on a question that comes before any drawing: where your lot actually sits. Washington’s 2023 ADU law changed a lot. But “the state allows two ADUs” doesn’t mean every lot in Kitsap County gets two. Here’s how it breaks down in 2026 — urban, rural, Bremerton, and the pre-approved plans most homeowners don’t know exist.

This is general information, not legal or permitting advice. Code changes, so confirm your parcel with the right planning department before you spend money.

Start here: is your lot urban or rural?

The first question isn’t how big or how many. It’s whether your property is inside an Urban Growth Area (UGA) or inside city limits — or whether it’s in rural unincorporated Kitsap County. The state ADU law in RCW 36.70A.681 mainly applies inside urban growth areas. Rural lots follow Kitsap County’s rural ADU rules, and those are much tighter.

Not sure which one you are? Call Kitsap County DCD. It’s a five-minute question that can save you real design money.

Urban unincorporated Kitsap (UGAs) Rural unincorporated Kitsap City of Bremerton
Code KCC 17.415.010 KCC 17.415.015 BMC 20.46.010
How many ADUs Up to two per lot One per lot One house plus two ADUs
Maximum size 1,000 sq ft, measured on the inside Attached: 50% of the main home’s habitable area. Detached: the smaller of 50% or 900 sq ft 1,000 sq ft or 60% of the main home’s habitable area, whichever is greater
Owner must live there? No — state law bars the requirement Yes, in the main house or the ADU No

Urban unincorporated Kitsap: more room than most people expect

Silverdale, Kingston, Central Kitsap, and the other UGAs outside city limits follow Kitsap County Code 17.415.010.

How many and how big

You can have up to two ADUs per lot, attached or detached. Each can be up to 1,000 square feet, measured on the inside — and the director may allow an ADU on a single floor of the existing house to equal the size of the main home. An urban ADU must have urban sewer and meet water rules.

One detail that matters for conversions: ADUs built entirely inside an existing structure don’t have to meet current setbacks or lot coverage, as long as the footprint doesn’t grow.

Parking

Under county code, a single ADU doesn’t need an extra parking space if the main house already meets its parking requirement, on-street parking is available, or the ADU is within half a mile of a major transit stop. A second ADU needs one more off-street space. State law (RCW 36.70A.681(2)) also caps how much parking a city or county can require.

Owner occupancy

State law says a city or county may not require the owner to live on the property with an ADU in these areas (RCW 36.70A.681(1)(b)). For investors, that’s a big deal — and it’s one of the biggest differences between urban and rural lots.

The other state-law guardrails worth knowing inside UGAs: Impact fees on an ADU can’t exceed 50% of what the main house would pay. Height limits can’t be lower than 24 feet unless the main house’s limit is lower. You can’t be required to build street improvements. Garage conversions must be allowed even if the garage doesn’t meet current setbacks. And an ADU can be sold separately as a condominium unit if it’s legally set up that way.

Rural Kitsap County: where expectations and reality are furthest apart

The rural version of this conversation usually starts with space. There’s plenty of land, so why not a cottage for Mom or a rental out back? But having room isn’t the same as having approval. Rural ADUs follow a different and much tighter set of rules — Kitsap County Code 17.415.015.

One ADU, and the owner lives on site

Rural lots get one ADU per lot — attached or detached, not both. And unlike urban areas, the owner must live on the property, in either the main house or the ADU.

An attached ADU can be no more than 50% of the main home’s habitable area, inside an owner-occupied home. A detached ADU is capped at 50% of the main home’s habitable area or 900 square feet, whichever is smaller. It has to be within 150 feet of the main house or be a conversion of an existing detached building like a garage. It must keep the look of the main residence and share the same driveway entrance. Mobile homes and RVs don’t count as ADUs.

The extra step: a Conditional Use Permit

In rural zones, Kitsap County DCD may also require Conditional Use Permit (CUP) approval — especially for detached ADUs — with its own fees on top of building permits. That adds time and cost. Check with DCD early and budget for it from the start, not after the drawings are done.

Septic and water: often the deciding factor

A rural ADU has to meet Kitsap Public Health District standards for water and sewage. If your septic was sized for a three-bedroom house, adding a unit may mean a bigger or new system. That’s often the deciding factor, which is why a licensed septic designer belongs at the front of the process, not the end.

“On rural land, the question isn’t whether you have room for an ADU. It’s whether your septic, your setbacks, and your permit path have room for one.”

City of Bremerton: its own code and its own rules

Bremerton follows its own code (BMC 20.46.010). Per the city’s ADU handout, ADUs are allowed anywhere a single-family home is allowed, up to one house plus two ADUs (three units total). Size can be 1,000 square feet or 60% of the main home’s habitable area, whichever is greater. There’s no owner-occupancy requirement, and no parking required for ADUs (code change effective June 16, 2025).

ADUs follow the zone’s setbacks, height, and lot coverage. They can sit right on a rear property line along an alley, and as close as 3 feet to a side line if the wall meets fire-separation standards. The design should blend with the main house — in the handout’s words, “no duplex-like designs.”

Port Orchard, Poulsbo, and Bainbridge Island each have their own codes, so check with your city’s planning department before you design anything.

Pre-approved ADU plans: the best-kept secret in the county

This one surprises people. Kitsap County and its cities offer pre-approved ADU plan sets that have already been reviewed for building code. That speeds up permitting and cuts design costs.

According to Kitsap County DCD, the plans are free in urban unincorporated Kitsap and in Bremerton, Bainbridge Island, Port Orchard, and Poulsbo, as long as you don’t change them. In rural areas they’re available for a fee. Options range from a 480 sq ft cottage (“Lille”) to 600 and 800 sq ft models, including a two-story design and garage-plus-ADU plans.

The fee picture, honestly: DCD lists approximate permit fees of roughly $4,700–$7,200 depending on the plan. Rural properties also pay CUP fees plus a $1,000 design fee. These are estimates that don’t include everything, so ask DCD for a real number on your parcel.

ADU vs. guest house: what you call it doesn’t matter

Kitsap County clarified this in July 2025. An ADU has both a kitchen and a bathroom. A guest house has one or the other, not both, and can’t be rented separately. Calling it a “studio” doesn’t change anything — the county looks at what’s actually built.

What I tell clients before they start

The order you do things in matters more than most people expect. Spending money on drawings before the basic questions are answered is how a good idea turns into an expensive one.

Confirm urban or rural for the exact parcel — not the neighborhood, and not what the lot next door did. Check septic or sewer capacity before paying for drawings. Price the whole project: permits, CUP, utilities, and site work. And run the rent and resale math separately, because cash flow and resale value aren’t the same thing.

Buying a home that already has an ADU? Confirm it was permitted. Unpermitted units are common here.

Quick answers: Kitsap County ADU questions

Can I build two ADUs on my lot in Kitsap County?
If you’re in an urban growth area or a city like Bremerton, generally yes — up to two. On rural land in unincorporated Kitsap, it’s one ADU per lot.

Do I have to live on the property to have an ADU?
Not in urban areas or Bremerton. State law bars owner-occupancy requirements there. On rural Kitsap County land, the owner must live in either the main house or the ADU.

How big can a detached ADU be on rural land?
The smaller of 900 square feet or 50% of the main home’s habitable area, and within 150 feet of the main house (or a conversion of an existing building).

Are pre-approved ADU plans really free?
In urban unincorporated Kitsap and the four cities, yes, if you don’t modify them. You still pay permit fees. Rural properties pay for the plans plus CUP and design fees.

Thinking about an ADU, or buying a property that has one?

An ADU can be a great answer — for family, for income, for flexibility down the road. But the lot decides what’s possible, not the floor plan. Knowing your zoning, your septic, and your permit path before you commit means you’re deciding based on what the property can actually support, not on what you hoped it could.

I help Kitsap homeowners and investors figure out what a property can actually support before they commit — zoning, septic, permitting, and the numbers. Book a free 30-minute call or send me a message and tell me about your lot.

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