ADUs + DADUs

ADU and DADU Design-Build, From Planning to Move-In

NorthLight designs and builds ADUs (Accessory Dwelling Units) and DADUs (Detached Accessory Dwelling Units) for homeowners in North King County, South Snohomish County, and the Eastside. An ADU adds a self-contained living space to your property, with its own sleeping, kitchen, and bathroom areas, for a family member, adult children moving back home, a home office, or another long-term use.

Because NorthLight is a design-build remodeling company, one team handles your ADU from early feasibility and space planning through design, permitting where required, construction, and the final walkthrough.

ADU vs. DADU: What’s the Difference?

Both are self-contained living spaces on the same property as your main home. The difference is where they are built:

  • ADU (Accessory Dwelling Unit): built as part of your existing home, such as an addition or a converted portion of the house.
  • DADU (Detached Accessory Dwelling Unit): built as a separate, standalone structure elsewhere on your lot.

Which option works best depends on your property, your goals for the space, your budget, and the local zoning and building codes that apply. NorthLight reviews those factors with you early, before design work moves forward.

ADUs are a significant investment, so the team works within your budget guidelines without sacrificing quality, and helps you understand where design choices affect cost and long-term value.

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Why Homeowners Add an ADU or DADU

An ADU adds livable space to your property without requiring you to move. Homeowners typically consider one for:

  • Family living space: a private place for parents or other relatives, including family members who want to age in place close by.
  • Adult children or guests: separate space with its own entry, kitchen, and bath.
  • A home office or studio: dedicated room to work away from the main house.
  • Long-term flexibility: a space whose use can change over time, including as a rental unit where local rules allow.

If you mainly need more room inside your existing home, a whole-home remodel or addition may be a better fit. NorthLight can help you compare options during your first meeting.

Our ADU and DADU Design-Build Process

  • Serving North King County, South Snohomish County, and the Eastside, we start with an introductory meeting to learn how you want to use the new space and why. We’ll talk through your goals, review the local zoning and building code considerations that affect an ADU on your property, and provide a preliminary estimate so you can see whether the project fits your budget before moving forward.

  • If NorthLight is the right fit, the next step is a Pre-Construction Services Agreement. This is the Develop and Design stage of our Develop → Design → Construct → Complete process, where your scope, layout, selections, and price are defined before construction begins. You’ll work closely with our Sales, Design, and Project Development team to plan the space.

  • During Pre-Construction, we take precise measurements, develop concept layouts for the ADU or DADU, and determine whether engineering, architectural input, or permits are required. We gather exact quotes from trade partners (electricians, plumbers, and others) and run budget checks along the way, leading to a fixed-price Construction Agreement.

    We also help you choose finishes and fixtures. For some, choosing finishes is a fun process; for others it can be overwhelming. Our design specialists can help you every step of the way, whether you just need someone to bounce ideas off or want us to meet you at the store. Once your selections are made, we can incorporate them into a project rendering if that is your preference.

  • Before construction begins, you’ll meet your Project Manager and Lead Carpenter, who stay with your project from start to finish. You can follow the schedule, receive updates, and ask questions in Buildertrend, our project software. As a BIAW Certified Builder, our team builds your ADU to last with quality materials, standards, and workmanship.

  • When construction is complete, we conduct a final walkthrough with you to make sure everything meets your standards and ours. Your project is covered by NorthLight’s 12-month workmanship warranty, and we follow up near the end of that period to handle any minor adjustments. We like to think of our customers as friends we gain and will always be here for in the future.

ADU and DADU FAQs

  • An ADU (Accessory Dwelling Unit) is built as part of your existing home, such as an addition or a converted portion of the house. A DADU (Detached Accessory Dwelling Unit) is a separate structure on your lot. Both are self-contained living spaces, and the right choice depends on your property, goals, budget, and the local codes that apply.

  • NorthLight ADU and DADU projects typically range from $400,000 to $1,000,000 or more. Size, whether the unit is attached or detached, site conditions, utility connections, and your finish selections all affect where a project lands. This is a typical range, not a quote. Your final price is set during Pre-Construction through a fixed-price Construction Agreement.

  • It depends on your lot and the zoning and building codes where you live, which is why NorthLight reviews local requirements early, starting at your first meeting. If engineering, architectural input, or permits are needed, the team identifies that during Pre-Construction, before construction is priced and scheduled.

  • Yes. Where permits are required, NorthLight handles the permitting and inspection process for you as part of design-build. Applications are typically submitted once your Construction Agreement is approved, or earlier during Pre-Construction when that helps avoid delays to your construction start. Learn more about permits, timelines, and costs on our FAQ page.

  • Pre-Construction is where your ADU is planned and priced. NorthLight takes measurements, develops concept layouts, helps you make selections, gathers exact trade-partner quotes, and runs budget checks so the plan stays aligned with your budget. It ends with a fixed-price Construction Agreement, so you know the scope and price before construction starts.

  • Your Project Manager and Lead Carpenter stay with the project from start to finish, and you can follow the schedule, receive updates, and ask questions in Buildertrend, NorthLight’s project software. After a final walkthrough, the project is covered by a 12-month workmanship warranty.

Plan Your ADU or DADU With NorthLight

Ready to talk about adding living space to your property? Contact NorthLight to schedule an introductory meeting. You can also learn more about our process or explore our other remodeling services.

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