What HB 1337 does
HB 1337 is the Washington law that sets minimum ADU rules every city and county planning under the Growth Management Act must follow. It applies inside urban growth areas: every Kitsap city and the county's UGAs.
Local governments had to update their ADU codes within six months of their comprehensive plan periodic update; the first deadline was June 30, 2025.
The main rules
| Topic | What the state requires |
|---|---|
| Number of ADUs | At least two ADUs per lot, in addition to the main house, on lots that meet the minimum lot size for the main house. |
| Size | A city or county can't cap ADU size below 1,000 gross square feet. |
| Owner occupancy | Can't be required of either the main house or the ADU. |
| Parking | Must be flexible; no on-site parking can be required within half a mile of a major transit stop. |
| Impact fees | No more than 50% of the impact fees charged for the main house. |
| Design and setbacks | Can't be stricter for the ADU than for the main house (entry doors, design review, setbacks, yard coverage, tree retention). |
| Street improvements | Can't be a condition of an ADU permit. |
| Selling the ADU | An ADU built as a condominium unit can't be barred from separate sale just because it began as an ADU. |
| HOAs | New covenants can't restrict ADUs; existing CC&Rs stay in effect. |
What it means in Kitsap
Every Kitsap city and the county's urban growth areas are covered. In practice:
- You can plan for an ADU even if you'll rent out both units.
- A 1,000 square-foot plan like the Salish is within what jurisdictions must allow.
- Ask about impact fees early; the state cap often makes them much smaller than people expect.
Local codes and handouts are still catching up. Kitsap County's code now allows up to two ADUs per lot in its urban growth areas. Bainbridge Island updated its ADU rules in October 2025, but its pre-approved ADU handout still lists one ADU per parcel. We confirm the rule in effect for your lot before you commit.
Rural lots
HB 1337's minimums apply in urban growth areas. Rural Kitsap lots follow the county's own ADU rules: one ADU per lot; a detached ADU limited to 900 square feet or half the main house's living area, whichever is smaller, within 150 feet of the house; extra off-street parking; and the owner must live in the house or the ADU. Most need septic review by Kitsap Public Health.