An accessory dwelling unit puts a second living space on a single-family residential property, and in Woodinville, WA, that can mean a backyard cottage for a parent or a unit that brings in rental income. New Day Construction is a design-build firm and a full-service ADU builder in Woodinville, WA. Our ADU construction runs from the first sketch to the final walkthrough, and we work in King County and Snohomish County. We design, permit, and build the unit, and the sections below answer the top ADU questions that Woodinville, WA, homeowners need to know before they hire an ADU contractor. Request a consultation, and we guide the permit paperwork from day one and help you find the best fit for your lot.
Choose the right ADU for your Woodinville, WA property
The best ADU for your lot is the one the property actually supports, so start with the types.
- Detached ADU. A new detached unit, also called a backyard cottage or a studio, in the yard. It starts from bare ground, so site work and the foundation take real effort.
- Attached ADU. A unit joined to the main home, the layout behind most in-law suites.
- Garage conversion. An existing garage becomes a living space. You skip a new foundation, but you still need insulation and utilities, plus a proper entry.
- Basement conversion. An existing basement becomes a separate unit, so stairs and daylight get checked first, along with ceiling height.
Every type shares the same backbone of survey, drawings, permits, construction, and inspection. A detached ADU is the most versatile, with a custom layout that suits the yard, and a garage conversion is often the shortest path, but neither is automatic on a given parcel.
Washington ADU rules, zoning laws, and permits in Woodinville, WA
Building accessory dwelling units in Washington means two layers of rules, the state's and the city's.
Washington's RCW 36.70A.681 requires cities in urban growth areas to allow at least two ADUs per lot, attached or detached, and to allow conversions of existing structures such as a detached garage. It bars owner-occupancy requirements, caps the impact fee at 50% of the fee on the main home, and keeps cities from capping ADU size below 1,000 gross square feet. The Municipal Research and Services Center summarizes the state ADU rules, including the point that each city applies them when its periodic plan update is due. A 2026 change, HB 1345, lets certain counties allow detached ADUs outside urban growth areas.
Local zoning laws and local building codes cover the rest, including setbacks, height, lot coverage, and design standards. We could not open Woodinville's current ADU code while preparing this page, so confirm the present limits with the City of Woodinville before you pay for plans. Do not assume a neighbor's ADU sets the rule for yours.
An ADU needs a permit, and the plumbing and wiring carry their own approvals and inspections. For a detached unit the review covers the site plan, the structural plans, the energy code forms, and the utility connections. Review times vary by city, from about six weeks to as long as three months on jobs we have seen, so ask what the queue looks like today. If a property has a critical area or buffer, the state protections may not apply, and an HOA approves separately from the city.
Is your Woodinville, WA property suitable for an ADU?
Several factors decide it. Lot size and shape, the footprint of the main home, access for equipment, slopes, trees, drainage, and where the utilities sit all matter. Sewer and water connections are the first question on a lot served by the city. Where there is no sewer, septic feasibility and perc testing (a soil drainage test) come first, and septic capacity can limit how many bedrooms the unit may have. Send us the address and the survey, if you have one, and we will review the home's utilities and tell you what we see and which questions go to the city.
Design, floor plans, and construction in Woodinville, WA
Good design starts with the site and the way the people in the unit will live. A functional detached ADU plans for sleeping, cooking, bathing, and storage together, with natural light and a step-free entry if mobility may matter later. We use 3D rendering so you can see the layout before the frame goes up, and you can bring your own architect if you prefer.
On our home additions the architect stage runs 1 to 3 months, and structural engineering with stamping adds about 2 more before city review begins. A detached ADU follows the same order, so plan on that rhythm and ask for a written timeline.
As general contractors, we run the trades. Excavation, foundation, plumbing, and electrical usually go to subcontractors, and the project schedule follows the construction sequence. Siding and windows can be done in-house on a small scope and are subbed out on a large one, and drywall usually goes to a sub. We coordinate the permit and the inspections while the construction crews work on your project, and one team keeps design and construction connected, which helps streamline the schedule. A structural engineer is the expert to call on walls and foundations, and their engineering expertise goes into the stamped plans, together with code compliance checks.
What an ADU costs in Woodinville, WA
On our price list an ADU starts from $200,000, a garage conversion from $200,000, and a basement remodel from $100,000 (price list, November 2026). A unit with its own kitchen and bathroom costs more, and a renovation of an existing space costs less than new construction, and the final cost depends on the lot and plans, plus the finishes.
Site access, the foundation, utility connections, structural design, and permit fees move the budget most. Washington state law caps the impact fee on an ADU at 50% of the fee on the main home, which softens one line. For a big job like this, we collect current bids from our foundation, electrical, plumbing, framing, roofing, and window subcontractors before we fix a price, so the estimate follows today's market, and we do not underbid you. We bid the same all year.
Our aim is to be on budget and on time. A change comes from two places: scope you add or a condition nobody could see before excavation, and we name those risks before you sign. Ask for a written scope that separates what is included from what is excluded, with a transparent list of allowances, because a planning figure is not a final price while plans are open. Whether an ADU is a smart investment, and what it adds to your property value, depends on your market and your plan, so talk to a local agent or lender before you count on a number.
Renting out an ADU or housing a family in Woodinville, WA
Washington does not let cities require the owner to live on the property, so both uses are open in principle. Rental income can offset the cost, and a unit for family keeps relatives close without sharing walls. Check your lender and your HOA, plus any city rule on short-term stays before you decide. A Lynnwood client's plan is to rent out the main home and both secondary units, which shows how far owners take the idea.
A garage ADU and a detached ADU in Lynnwood
This project is not in Woodinville. It is in Lynnwood, in Snohomish County, and it is the closest ADU work we can point to today.
A Lynnwood homeowner first had us convert a garage into an ADU. We are now building a 1,200 sq. ft. detached ADU for the same client. The unit is still in progress, so we have no final cost or photos to share yet. The two jobs cover the range, since one reuses a building that already stands and the other starts from an empty yard, and our experience with both helps you decide which fits your lot.
ADU contractors near Woodinville, WA | What to ask local professionals before you hire
Several ADU builders, general contractors, and design-build firms work in and around Woodinville, WA, and the wider Seattle area, and the right comparison is the same for each. We also build custom homes and handle home building from the ground up, but we do not specialize in small one-day jobs. Ask every ADU contractor the same questions, then compare the proposals.
- Who coordinates with the architect and the engineers?
- How are permit responsibilities divided between us?
- When do I need to lock in selections?
- How will a change be documented and priced before the work proceeds?
Check each contractor's registration. Washington registers contractors with Labor & Industries under RCW 18.27. Our registration number is NEWDADC823QR, and the L&I Contractor Verify tool shows its status along with bond and insurance details. Ask to see completed work and get warranty terms in writing. We provide a two-year craftsmanship warranty on completed work, and manufacturer warranties on installed materials pass through to you. A contractor's reputation matters less than the written proposal, so weigh the proposal.
Frequently Asked Questions
Short answers to what Woodinville homeowners ask before an ADU project starts.
What should I know about building an ADU in Woodinville, including local zoning and permit requirements?
State law sets a floor for every city, including two ADUs per lot in urban growth areas and no owner-occupancy requirement. Woodinville's zoning code adds local limits on size, height, setbacks, and parking, and the unit needs a permit with its own inspections. Confirm the current limits with the city.
How do I choose an ADU contractor in Woodinville?
Check active L&I registration, bond, and insurance first, and ask each builder who coordinates the design. Then line up written scopes, ask how hidden conditions are priced, and ask to see completed ADU work. Get the warranty terms in writing.
How much does it cost to build an ADU in Woodinville?
An ADU starts from $200,000 on our price list as of November 2026, and the final figure depends on the lot and plans, plus the finishes. Site work and the foundation, plus utilities, drive most of the difference between projects.
Which contractors build ADUs in Woodinville or nearby areas?
Several general contractors and design-build firms do. We are one of them, with projects across King County and Snohomish County. Whoever makes your shortlist, check their L&I record before anything else.
What types of ADUs can I build, and how much space can they have?
You can build a detached ADU, an attached unit, a garage conversion or a basement unit, depending on the property. State law bars cities from capping ADU size below 1,000 gross square feet, and your city may allow more. Confirm Woodinville's limit before you design.
What is the process for planning, permitting and building an ADU?
It starts with a property review and a consultation. Design and structural engineering follow, then the plans go to the city. Construction begins once the permit is issued, with inspections along the way and a final walkthrough. We guide you through every step.
What factors affect whether my property is suitable for an ADU?
Lot size and shape, the main home, access, slopes, drainage, utility locations, any critical area buffers and an HOA. Share the address and survey for a first look.
Can I rent out an ADU or use it for family housing?
Yes, in principle. Washington bars owner-occupancy requirements, so you can rent the unit or house a relative. Check your lender and your HOA, plus local short-term rental rules, first.
Talk to us about your Woodinville ADU project
Tell New Day Construction about your property and the unit you have in mind, and request a consultation. Reach us at (425) 522-5748 or [email protected], or visit our Bellevue showroom at 1850 130th Ave NE #1, Bellevue, WA 98005. More about our ADU builder service, custom home builders service, home addition contractor service and home remodeling is on our service pages.
