Detached ADU
Allowed since the 2025 code update. The city's pre-approved plans program lists 1,200 square feet and 24 feet as the maximums, and the unit counts toward the property's total units.
AIM Builders / ADU construction / Bellevue
ADU Builder in Bellevue, WA
Bellevue has allowed attached ADUs since 1993, and detached ADUs became legal on its residential lots in 2025. AIM Builders has completed kitchen, bathroom and whole-home work in Bellevue. For an ADU we start with your lot, the city's current numbers and your utilities, 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 Bellevue
What Bellevue allows now.
The city's original attached ADU rules changed very little until 2023. That year's ADU reform removed the owner occupancy requirement, allowed an ADU to be sold to a separate owner and raised the size limit from 800 square feet to 1,200 square feet or 40 percent of the structure, whichever is larger. Detached units were still not allowed at that point.
On June 24, 2025 the City Council adopted middle housing code changes to meet the state's HB 1110 and HB 1337 requirements. ADUs and middle housing, detached ADUs included, are now allowed on lots zoned predominantly for residential use. The city's pre-approved plans program lists a detached ADU at a maximum of 1,200 square feet and 24 feet tall, with up to 28 feet allowed when it is built above an existing garage.
One council decision matters for planning. A detached ADU counts toward the total number of units on the property, and an attached ADU does not. The council also kept parking requirements, with exemptions near major transit.
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
Permits and site work in Bellevue.
Bellevue treats a permitted ADU as a regular dwelling unit when it decides which permit applies. A building with one or two units, such as a detached ADU, uses the one and two family residence (BS) permit. When a project includes several buildings that each contain dwelling units, the city also requires a Clearing and Grading site permit so the whole site is reviewed together, and the plans for both permits must match. We confirm with the city early whether your project needs that site permit.
For water and sewer, the city points applicants to a Utilities representative. On a sloped or wooded Bellevue lot, where the unit sits, how equipment reaches it and how far the line runs to the sewer main drive much of the cost, so we look at all three on the first visit.
ADU types in Bellevue
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.
Bellevue ADU questions
Questions we hear in Bellevue.
Are detached ADUs allowed in Bellevue now?
Yes. The City Council adopted middle housing code changes on June 24, 2025 that allow detached ADUs on lots zoned predominantly for residential use. Older city pages that say detached ADUs are not allowed were written before that change.
How big can a detached ADU be in Bellevue?
The city's pre-approved plans program lists a maximum of 1,200 square feet and 24 feet in height for a detached ADU, with up to 28 feet when it sits above an existing garage. We confirm the numbers for your zone and lot before design.
Do I have to live on the property to have an ADU in Bellevue?
No. Bellevue removed its owner occupancy requirement in the 2023 ADU reform, and state law no longer lets cities require it.
Does Bellevue offer pre-approved ADU plans?
Not yet. The city is developing a pre-approved plans program for detached ADUs and cottage housing. Until it launches, each detached ADU is designed for its own lot.
What does a Bellevue ADU cost?
Every ADU gets a written, itemized estimate after we see the property. The type of unit, the distance to sewer and water, slope and access set the number, so we do not quote before the site visit.
Step 1 of 2Your project
Request a free ADU consultation in Bellevue
Let’s plan your adu or garage conversion.
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Roof repair is available only as part of a larger remodeling scope.
Planning an ADU in Bellevue?
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 Bellevue.
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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