Make your living area bigger with the expert ADU Washington State building services from Interbay Construction. We create and build ADUs with fresh ideas, top materials, and skillful work to give you a space that meets your needs. Whether you need a guest house, rental unit, home office, or in-law suite, our skilled ADU contractor takes care of every detail carefully. From planning and getting approvals to building and finishing touches, we provide a smooth process that gives great results. Our focus on quality and making customers happy ensures your ADU improves both use and property value. Let us help you make your dream a reality!
We make your dream ADU Washington state come true with great craftsmanship and smart ADU plans. Whether you want to build a guest house, a rental unit, a home office, or a space for family, we promise a smooth journey from beginning to end. Our team focuses on function, style, and quality materials to build an ADU that fits your lifestyle and home. We serve Bellevue, Seattle, and nearby areas. We are the ADU contractors that homeowners trust. Reach out to us today!
At Interbay Construction, we have a full range of ADU Washington State construction services to create an elegant, functional, and customizable living space. Our services include:
Let us help you build the perfect ADU in Washington State with expert craftsmanship and careful attention to every detail. Whether you’re planning a cozy guest house, a rental unit, or a functional home office, our experienced ADU contractors will work with you to create a space that’s stylish, practical, and built to last!
Washington changed its ADU rules, and most homeowners have not caught up. Inside the state’s designated urban growth areas — which take in Seattle, Bellevue and most of the Puget Sound cities we build in — the Washington State Department of Commerce states that most cities and counties must now:
Local code that conflicts with the state statute (RCW 36.70A.680–.681) is preempted, so a restriction you read about a few years ago may no longer apply to your address. The details still vary at the edges, which is why we confirm what applies to your specific parcel before any design work begins.
The Seattle Department of Construction & Inspections draws a clear line between the two. An AADU is a permitted unit inside the existing house. A DADU is a permitted unit on the same property but not within the house — the backyard cottage most people picture. Neither can be subdivided from the main house, and neither is legal until it has been established through the permit process.
Both count toward the lot’s density limits, and both must comply with the zone’s height and location standards. A larger lot might support four or more units in total, but only two of them can be ADUs. Three requirements that apply to a main house do not apply to an ADU in Seattle: parking, street improvements, and mandatory housing affordability contributions.
The item that catches people out is sewer. SDCI reports every ADU permit to King County for a sewage treatment capacity charge, and you will sign an acknowledgement of that charge as part of your application.
A tiny house on wheels is not an ADU. Seattle treats it as a camper trailer, and it cannot be lived in on a lot inside city limits. A tiny house on a permanent foundation is considered a DADU and is permitted as one.
Your site, more than your wishlist, drives the design. An ADU has to meet current Seattle residential, building, mechanical, electrical, energy, land use, environmentally critical areas and shoreline standards. A steep slope, a watercourse or a critical-areas designation changes what can be built and where, which is why we walk the lot before proposing a layout.
There is a faster route if you do not need a bespoke design. Seattle maintains a gallery of pre-approved DADU plans through its ADUniverse programme, which removes a significant part of the design review. The city also publishes its own guidance as CAM Tip 116A for attached units and CAM Tip 116B for detached ones.
We design and build both attached and detached accessory dwelling units across Seattle, Bellevue and the surrounding Puget Sound communities. If you are weighing whether your lot works for one, the site visit and the code check come before the drawings.
At Interbay Construction, we are committed to every ADU Washington State project we take on. Using high-quality materials and reliable construction techniques, we build ADUs that are not just durable and stylish but also a great addition to your property. Whether you’re looking to add a guest house, rental unit, or home office, our experienced ADU contractors are here to bring your vision to life. We focus on clear communication, staying on schedule, and achieving outstanding results. Let’s build an ADU that’s comfortable, practical, and built to last, creating a space you’ll enjoy for years to come!
