ADU builders in Seattle
A second home on your own lot — for family, for rental income, or for the flexibility to stay where you already live. We design, permit and build detached and attached ADUs across Seattle and the Eastside.
Four ways to add a second unit
Which one fits depends on your lot, your budget and what the city will allow — and that is the first thing we work out with you.
Detached ADU (DADU)
A free-standing backyard cottage with its own entrance, kitchen and bathroom. The most private option, and the one with the strongest rental appeal.
Attached ADU
Built onto the existing house as a self-contained unit. Usually cheaper to service, because the utilities are already close by.
Garage conversion ADU
The fastest route to a legal second unit when the structure is already there. See our garage conversions.
Basement ADU
A separate unit below the main floor, with its own access. Ceiling height and egress decide whether it is possible — we check both early.
A finished ADU, inside and out
A detached unit we designed, permitted and built in the Seattle area — from the front door to the shower tile.
What an ADU actually costs and takes
Straight answers, not ranges so wide they tell you nothing.
Typical build cost
Driven by location, design complexity and how far the utility hookups have to run. We price each project individually after the site visit.
Design to completion
Depending on the scale of the project and how the permitting process runs. You get a schedule before construction starts.
Are eligible
Most single-family lots in Seattle can take an ADU, but zoning, lot size and existing structures all affect it. We assess your site during the consultation.
Seattle ADU rules, in plain English
Permits are required by the Seattle Department of Construction & Inspections (SDCI) for all new dwellings, ADUs included. We file them for you — it is part of the job, not an extra you chase separately.
Our in-house architecture and engineering team handles the drawings and the submission, so the design that gets approved is the design we build.
- Zoning and lot size decide whether a detached or attached unit is possible — we check this before you spend anything on design.
- Existing structures on the lot count toward what you are allowed to build.
- Utility hookups are one of the biggest cost variables. How far the water, sewer and power have to travel matters more than square footage.
- Egress and ceiling height are what usually decide a basement conversion.
- Parking, setbacks and height limits are all set by the city, and they change — we work to the rules current at the time you file.
From first call to finished unit
Free consultation
We visit the property, take measurements and tell you honestly what your lot will and will not allow.
Design & fixed price
Drawings, a detailed scope and a fixed price before construction begins — no open-ended estimates.
Permits filed
We prepare and submit the SDCI application and manage the process through to approval.
Build & handover
One project coordinator, regular updates, inspections managed, and a signed completion form at the end.
ADU questions, answered
What is the average cost to build an ADU in Seattle?
An Accessory Dwelling Unit in Seattle can cost between $120,000 and $300,000+, based on location, design complexity and utility hookups.
Is my property eligible for an ADU or DADU?
Most single-family lots in Seattle are eligible for ADUs, but zoning, lot size and existing structures may affect your ability to build. We assess your site during the consultation.
Do I need a permit for an ADU in Seattle?
Yes. Permits are required by the Seattle Department of Construction & Inspections (SDCI) for all new dwellings, including ADUs. We handle the filing.
How long does an ADU take to build?
A typical ADU project takes 4 to 9 months from design to completion, depending on the project scale and the permitting process.
What is the difference between an ADU and a DADU?
A DADU is a detached accessory dwelling unit — a separate structure in the yard. An ADU can also be attached to the house or created inside it, such as a basement or garage conversion.
Will an ADU increase my property value?
Yes — an ADU can significantly increase your home’s resale value as well as its rental income potential.
Can you handle the design as well as the build?
Yes. Levite Construction provides end-to-end service including architectural design, permit filing and project management, with an in-house designer on every project.
Which areas do you build ADUs in?
Seattle, the Eastside and the greater Puget Sound — 61 cities across King, Snohomish and Pierce counties, including Bellevue, Redmond, Kirkland and Everett.
Find out what your lot will allow
Free in-house consultation across Seattle, the Eastside and Puget Sound — including an honest read on whether an ADU works on your property.