If you own a property on Bainbridge Island, and are considering adding an ADU, here is what you need to know from a zoning perspective.

Can I build an ADU on Bainbridge Island?

The good news is ADUs are allowed as an accessory use on almost all residentially zoned properties. This means you don’t need any additional permissions or Zoning adjustments. As long as the design meets the regulations no special approvals will be necessary. This is great as many cities have been slow to adopt ADU codes.

What types of ADUs are allowed?

Accessory Dwelling Units on Bainbridge Island can be either detached, stand-alone units, created within an existing home (a basement conversion for example), and can even be built over a garage. My personal recommendation is that detached ADUs are the best option for most properties, although we have designed all sorts of ADUs over our career. ADUs over garages are a great way to add a rental unit without taking up too much land and have been very popular.

How many ADUs can I build on my property on Bainbridge Island?

The Bainbridge Island ADU code does have a one ADU per property limit. This means that if you convert your basement into an accessory dwelling unit you won’t also be allowed to build a detached ADU. I think this is unfortunate as many other cities, including Seattle and Portland, allow multiple ADUs - for instance, a basement ADU and a detached ADU. Hopefully Bainbridge Island will reconsider this limitation as they work to increase housing options and affordability. I think allowing a basement ADU plus a detached ADU would be a great code change.

Do I need to provide parking for the ADU?

Providing parking is another requirement when adding an ADU to your Bainbridge property. At least one off-street parking space must be provided for the ADU tenants. They also must share the driveway with the main house - meaning you can’t have two separate driveway entrances.

What is the size limit for ADUs on Bainbridge Island"?

There are a few other requirements, although they are mostly targeted at detached ADUs. The size of ADUs are limited to 900sf or less, and they must meet all of the zoning requirements of the overall property (such as setbacks, lot coverage, etc.) Of note, if ADUs are built in the same structure as a garage the garage doesn’t count against the 900sf limit. Stairs within the ADU also don’t count against the size limitation. Also, if you are making an ADU in your basement the City will allow the ADU to be larger than 900sf if it is filling the existing basement space.

Here is the exact language from the Bainbridge Island Municipal Code, Title 18 Zoning, Chapter 18.09 Use Regulations:

Accessory Dwelling Unit.

a. An accessory dwelling unit (ADU) may be created within, or detached from, any single-family dwelling, whether existing or new, as a subordinate use, where permitted (“P”) by this chapter.

b. In the shoreline jurisdiction, an accessory dwelling unit may be created within, or detached from, any single-family dwelling, whether existing or new, as a subordinate use, where conditional (“C”) pursuant to this chapter. See Chapter 16.12 BIMC for shoreline conditional use process.

c. Only one accessory dwelling unit may be created per parcel.

d. No variances shall be granted for an accessory dwelling unit.

e. One off-street parking space shall be provided in addition to off-street parking that is required for the primary dwelling.

f. Accessory dwelling units shall be designed to maintain the appearance of the primary dwelling as a single-family dwelling, containing 900 square feet of floor area or less. However, if the accessory dwelling unit will be located within a building existing as of the approval date of Ordinance No. 2015-16 (for example, in a basement) the city may allow an increased size in order to efficiently use all floor area. If a separate outside entrance is necessary for an accessory dwelling unit located within the primary dwelling, that entrance must be located either on the rear or side of the building.

g. If an accessory dwelling unit is constructed in conjunction with a garage, the square footage of the garage shall not count towards the 900-square-foot limitation.

h. An accessory dwelling unit not attached to the single-family dwelling may not contain any accessory use other than a garage.

i. No recreational vehicle shall be an accessory dwelling unit.

j. When stairs utilized for the ADU are enclosed within the exterior vertical walls of the building, they shall not count towards the floor area of the ADU.

k. The ADU shall share a single driveway with the primary dwelling.

l. School impact fees and qualified exemptions from those fees as provided in Chapter 15.28 BIMC shall apply.

m. All other applicable standards including, but not limited to, lot coverage, setbacks, parking requirements, and health district or city requirements for water, sewer, and/or septic must be met.

n. In the Mixed Use Town Center, new accessory dwelling units are only permitted as part of a housing design demonstration project single-family subdivision approved pursuant to BIMC 2.16.020.S.