Detached ADU
Up to 1,200 square feet and 30 feet tall under BMC 12.14.135, with its own footing and roof drains and its own connection to water and sewer service.
AIM Builders / ADU construction / Bothell
ADU Builder in Bothell, WA
Bothell sits in both King and Snohomish County, and ADU permits on either side run through the city. AIM Builders has completed kitchen and bathroom remodels in Bothell. For an ADU we start with your lot and the city's ADU checklist, then give you a written, itemized estimate.
Planning sketchStart with a plan
Make room for what comes next.
- Detached, attached, or a garage conversion?
- What's the intended use: rental, family, or a home office/studio?
ADU rules in Bothell
What Bothell's code allows.
Bothell's ADU standards are in BMC 12.14.135. A new ADU can be up to 1,200 square feet. Converting existing space can go larger with the Community Development Director's approval, as long as the ADU does not exceed 40 percent of the main home's gross floor area. A detached ADU can be up to 30 feet tall, or 33 feet over an existing accessory structure, and it is exempt from the rule that limits accessory buildings to five percent of the lot.
The city's middle housing page notes that HB 1337 requires cities to allow up to two ADUs on lots that allow single-family homes. The state law behind it also bars cities from requiring owner occupancy and caps ADU impact fees at half of what the main home would pay.
Applications go online through MyBuildingPermit.com under Single Family Residential, Accessory Dwelling Unit. The city requires its Assigned Address letter before it accepts the application. Impact fees for a new unit include traffic, fire and park fees, paid when the permit is issued.
Rules checked against the sources listed below on October 26, 2026. Codes change, so we confirm the current requirements for your address before design.
Lot and site
Utilities and drainage on a Bothell lot.
Water and sewer depend on who serves your street. A project that adds square footage or turns unheated space into living area needs a water and sewer availability certificate and a fire flow letter from the provider. If the City of Bothell is the provider, that availability request comes first and can take up to two weeks. Alderwood, Northshore and Woodinville customers go to their own provider.
Homes on septic need King County Health or Snohomish Health District approval when an ADU adds square footage or bedrooms. The site plan has to show contours and any sensitive areas, such as wetlands, steep slopes or streams, on or within 200 feet of the lot. Footing and roof drains need an approved discharge point. A detached unit keeps the same rear setback as the main house unless the lot is on an alley.
ADU types in Bothell
About our ADU construction Four ways to add a unit.
How it starts
From the first walk to a written estimate.
A consultation with Adi
Adi personally takes every in-home consultation. You talk through what you want to change, what matters daily and what you hope the home could do.
A walkthrough of your space
We measure, check structure and access, and look at the rooms as they are today, so the plan fits the house you actually have.
A written, itemized estimate and schedule
You see exactly what you are paying for, with the scope and schedule in writing before any demo starts.
Bothell ADU questions
Questions we hear in Bothell.
How big can an ADU be in Bothell?
Up to 1,200 square feet for a new ADU under BMC 12.14.135. A conversion of existing space can be larger with the Community Development Director's approval, as long as it stays within 40 percent of the main home's gross floor area.
Does it matter which county my Bothell home is in?
Permits run through the City of Bothell either way. The county matters for septic approvals, which go to King County Health or the Snohomish Health District.
I already have an unpermitted unit. Can it be made legal?
Bothell requires the owner to apply, and the city inspects the unit before any approval. If it was built without a building permit, the city checks that it is sound and meets code, and further permits may be required. We can look at the unit and scope any work it needs.
Do I need a separate address for the ADU?
Bothell's ADU checklist requires a copy of the city's Assigned Address letter before the application is accepted, so that request comes early in the process.
What does an ADU cost in Bothell?
We give a written, itemized estimate after a site visit. Distance to water and sewer, drainage, the type of unit and the city's impact fees all affect the total, so we do not quote before seeing the lot.
Step 1 of 2Your project
Request a free ADU consultation in Bothell
Let’s plan your adu or garage conversion.
We’ve selected the service you were exploring. Continue with it or choose another below.
Roof repair is available only as part of a larger remodeling scope.
Planning an ADU in Bothell?
Talk it through first.
Share your address and what the unit is for. Adi personally takes every in-home consultation, and the walkthrough covers the lot, access and utilities before any design or price.
Call (425) 671-2917Keep planning
ADU pages for nearby cities.
Each page covers that city's own ADU rules and permit process.
Free In-Home Consultation
Let’s look at your lot in Bothell.
Tell us what you would like to change. Adi visits, measures and listens, and you receive a written, itemized estimate with one point of contact from the first walkthrough to the final details.
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