ADU construction
ADU Construction Services
Backyard cottages, garage and basement conversions, and detached accessory dwelling units. We check whether your lot qualifies first, then design, permit, and build it as a real home.
An ADU is decided by your lot before it is decided by your budget. Setbacks, coverage, zoning, and utilities settle what is possible, and getting that wrong is how a project dies on paper. We check feasibility first, then build a unit warm and dry enough to rent or move family into for the long haul.
Why choose us
Why choose us for your ADU
01
We tell you if your lot qualifies first
Lot size, setbacks, coverage, and zoning decide an ADU before anything else. We run feasibility before you spend a dollar on design, so you are not paying for a plan your lot cannot permit. If it will not work, we tell you early, when it is still free to find out.
02
The number is settled before we build
ADU budgets get surprised by the parts people do not see coming, utility connections, site work, and fees. We itemize the whole scope, put real allowances on selections, and lock it before we start, so the estimate is the number, not the opening bid.
03
Built as a real home, not a shed with a bathroom
An ADU you can rent or move a parent into has to be warm, dry, and quiet for the long haul. We build it to the same standard as the main house, real insulation, real systems, real waterproofing, not a finished outbuilding.
04
One contract from feasibility to final inspection
Feasibility, design, permits, utility connections, the build, and the certificate of occupancy under one roof. You call one number, and the person who answers owns the whole thing, including the parts that trip up most ADU projects.
Avoid these
Common ADU construction mistakes to avoid
Six ways ADU projects go sideways, most of them before construction even starts. Knowing them is most of what keeps a project from stalling.
Design happens before the lot is checked
Paying for plans before confirming setbacks, coverage, and zoning is how ADU projects die on paper. We run feasibility first, so design starts on a lot that can actually permit it.
Utility connections are underestimated
Water, sewer, and electrical for a second dwelling can mean a new side sewer, a service upgrade, or capacity fees. We scope utilities up front, because that is where ADU budgets get surprised.
Parking and access rules are missed
Rules on parking, separate entrances, and construction access have changed and vary by city. We confirm the current rules before committing to a layout.
It is built like an outbuilding
Thin insulation, cheap systems, and skipped waterproofing make an ADU cold, damp, and hard to rent. We build it to the same standard as the house.
The site is treated as flat and simple
Grade, drainage, trees, and construction access can add real cost that a quick quote ignores. We assess the site before pricing, not after.
Nobody plans for how it will be used
A rental, an aging parent, and a home office want different layouts, entrances, and finishes. We design around the actual use, not a generic box.
Quality
What quality ADU construction looks like
An ADU is a small home, and it should be built like one. These are the things that make it comfortable and durable, not just permitted.
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A real foundation and drainage plan
Footings, grade, and drainage suited to the site, not a slab dropped on grade and hoped for.
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Insulation and envelope to code
A warm, quiet, efficient unit that meets Washington energy code and is comfortable year round.
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Proper utility connections
Water, sewer, and electrical connected and metered correctly, sized for a full dwelling.
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Waterproofing and roofing that last
The same detailing we put on the main house, so the ADU stays dry through wet winters.
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A layout that lives bigger than its size
Storage, light, and flow planned so a small footprint actually feels like a home.
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Finishes that hold up to renters or family
Durable, low-maintenance materials chosen for real, ongoing use, not just the listing photos.
Options
Types of ADUs
Most ADUs are one of these three. Which one fits depends on your lot, your goals, and your budget.
Level 01
Garage or basement conversion
Turning existing space into a legal attached ADU (AADU). Often the fastest path.
- Convert existing footprint
- Add a kitchen and bath
- Egress, insulation, and systems
- A separate entrance
What moves the price: whether the space is already conditioned and how far utilities have to reach.
Level 02
Detached ADU (DADU)
A new backyard cottage, built from the ground up with its own everything.
- New foundation and structure
- Full kitchen and bath
- Utilities run to the unit
- Its own entrance and address
What moves the price: size, site conditions, and how far utilities have to run.
Level 03
Custom or two-story DADU
A larger detached unit with more rooms, or living space over a garage.
- Two-story or garage-under layouts
- Full systems and insulation
- Higher-end finishes
- More site and structural work
What moves the price: size, structural scope, and finish level.
Rules & permits
ADU rules and permits in Washington
ADU rules have changed fast in Washington, and they still vary city to city. Here is what shapes whether and how you can build one.
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Washington ADU law is expanding
State law has pushed cities to allow ADUs more broadly, with fewer parking and owner-occupancy hurdles than a few years ago. More lots qualify than owners expect. TKTK confirm current state and city rules.
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Every city writes its own rules
Within state law, each city sets its own size limits, setbacks, and design standards. We confirm the current rules for your specific lot. TKTK specifics by city.
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Utilities and the side sewer
A second dwelling may need a new or upgraded side sewer, water line, or electrical service, sometimes with capacity fees. We scope these early so they are not a surprise.
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Permits and plan review
ADUs go through their own permit and plan review, and timelines vary. We pull it and manage the process. TKTK typical review windows by city.
Service areas
ADU construction by city
ADU rules, permit offices, and local pricing change by city. Pick yours for the details that apply to your lot.
FAQ
ADU construction FAQs
Can I build an ADU on my lot?
Maybe, and we check before you spend on design. Lot size, setbacks, coverage, and zoning decide it. Washington has expanded ADU rules recently, so more lots qualify than did a few years ago, but every city is different. We run feasibility first, when it is still free to find out.
What is the difference between an attached ADU and a DADU?
An attached ADU, or AADU, is within or attached to your house, often a basement or garage conversion. A detached ADU, or DADU, is a separate structure, usually a backyard cottage. They permit, connect, and cost differently, and we will help you decide which fits your lot and goals.
Do I have to live on the property?
Owner-occupancy rules have relaxed in much of Washington, but they vary by city and can change. We confirm the current rule for your address before you plan around it. TKTK confirm owner-occupancy by city.
Can I rent it out?
Usually yes, and rental income is one of the most common reasons owners build one. Rules on short-term versus long-term rental vary by city. We will tell you what applies to your address. TKTK confirm rental rules by city.
How long does an ADU take to build?
A garage conversion is faster than a ground-up DADU, and permits and utility connections usually drive the timeline. We put a schedule in writing and flag the real risks. TKTK typical ranges by type.
How much does an ADU cost?
It depends on type, size, site, and utility connections, so we price against your real conditions rather than a national average. See your city page for local ranges, or send the form for a free written estimate. TKTK local cost bands by city.
Ready when you are
Get a free ADU estimate
Tell us about your lot and what you want to build. We will check feasibility, call within one business day, and put a written estimate together with no pressure to sign.