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DADU & ADU Builder for the Greater Seattle Area
Custom detached accessory dwelling units and attached ADUs for Seattle, King County, and Snohomish County homeowners. Design, permitting, and construction under one contractor.
Why Puget Sound
Homeowners Build ADUs
Seattle's 2019 DADU ordinance and Washington's HB 1337 opened the door to accessory dwelling units across the Puget Sound region. Most single-family lots in Seattle can now support up to 2 ADUs, owner-occupancy is no longer required, and detached units can run up to 1,000 square feet within the city. Surrounding jurisdictions in King County and Snohomish County have their own rules, and we work within all of them.
Homeowners use ADUs to keep aging parents nearby, provide affordable housing for adult children, host guests, or generate rental income in a tight housing market. The most successful projects start with a clear vision of how the unit serves your family's needs and an honest read of what's buildable on your specific lot.
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ADU & DADU Services We Offer
We help homeowners choose the right accessory dwelling strategy for their lot, family goals, and budget. Each project is planned around site constraints, utilities, permitting, privacy, and long-term livability.
Detached Accessory Dwelling Units (DADUs)
Detached ADUs give you the greatest privacy and independence for family members, guests, or rental tenants. We manage siting, setbacks, grading, foundations, utility runs, and the build itself so the standalone unit works well both on paper and in daily life.
Attached ADUs
Attached units are a smart choice when you want to expand livable space while sharing part of the home's structure or systems. We plan separate access, privacy, fire separation, and building-envelope details so the new space feels intentional, not improvised.
Garage Conversions
The most cost-effective ADU path when your existing garage has the footprint and access to support it. We handle egress window installation, utility rerouting, fire separation, and the finish work that turns a garage into a code-compliant living unit.
Design-Build DADU Experts for the Greater Seattle Area
One general contractor from site survey through final inspection across Seattle, King County, and Snohomish County.
Transparent ADU Pricing
ADU costs vary by scope, but typical Seattle-area pricing includes:
- Garage conversions: $60,000–$100,000
- Attached ADUs: $90,000–$140,000
- Detached ADUs (DADU): $120,000–$200,000+
Costs rise with poor drainage, challenging soils, limited utility access, premium finishes, and complex setbacks. Seattle projects generally run higher than surrounding jurisdictions due to labor costs and more involved permitting. We provide itemized estimates showing exactly what you're paying for. No surprises. We explain cost-benefit tradeoffs so you can invest wisely, and many homeowners recover their investment through rental income within 10–15 years.
ADU & DADU Questions Answered
How many ADUs can I build on my property in the Seattle area?
Washington's HB 1337 and Seattle's 2019 DADU ordinance allow up to 2 accessory dwelling units on most single-family lots: an attached ADU plus a detached ADU (DADU). In Seattle, owner-occupancy is no longer required, and detached units can run up to 1,000 square feet. In unincorporated King County and Snohomish County, size limits often run up to 1,200 square feet with jurisdiction-specific setback and lot coverage rules. We review your site survey and property parcel data during the initial consultation to confirm exactly what's buildable on your lot.
What's the difference between an ADU and a DADU?
An accessory dwelling unit (ADU) can be attached to your primary home, built above a garage, or created through a garage conversion. A detached accessory dwelling unit (DADU) is a separate, freestanding structure on your property. Both count toward the 2-unit limit on most lots in Seattle and the surrounding region. DADUs are often preferred because they offer more privacy and independence for multigenerational living or rental use. They also have fewer structural constraints since they don't share a foundation or building envelope with the main house.
How long does an ADU project typically take?
From initial design through completion, most ADU projects take 5 to 8 months, though this varies based on permitting, weather, and scope. Seattle SDCI plan review for a DADU typically runs 4 to 10 weeks depending on queue length and whether the project triggers design review, SEPA, or tree code review. King County and Snohomish County reviews run on similar timelines. Once permits are approved, construction typically takes 12 to 16 weeks for a detached unit. We build detailed timelines during the design-build phase so you know exactly what to expect.
What are the main challenges with ADU construction in the Puget Sound area?
Regional soil conditions run from compacted glacial till to clay-heavy lots that drain poorly. Poor site drainage leads to foundation problems years down the road, so thorough site surveys and grading plans come before construction. Setbacks from roads and property lines limit where structures can sit. Utility connections matter, especially for detached units that need separate water, sewer, and electrical feeds. Fire separation codes between an ADU and the primary home have also tightened. These aren't reasons to avoid ADUs. They're reasons to work with a contractor who handles IRC code compliance as a checklist, not an afterthought.
Can I convert my garage into an ADU?
Yes, garage conversions are allowed across most Seattle-area jurisdictions and are one of the most cost-effective ADU options. You'll need proper egress windows for life safety, utility rerouting (especially if the water heater or electrical panel lives in the garage), and a plan for replacement parking or an alternate structure. Garage conversions also need fire separation from the main home depending on how they're attached. For older Seattle Craftsman homes, mid-century ranchers, or split-levels throughout the region, the existing garage footprint often supports a conversion without major lot disruption.
What does an ADU project cost?
ADU costs typically range from $75,000 to $200,000+, depending on size, finishes, and site conditions. A basic garage conversion might run $60,000 to $100,000. A new detached unit with mid-range finishes usually falls in the $120,000 to $180,000 range. High-end DADUs with premium materials and systems can exceed $200,000. Seattle projects generally run higher than surrounding jurisdictions due to labor costs and more complex permitting. What affects your cost: lot conditions, site survey complexity, design choices, and material selections. We provide transparent budgets and itemized estimates during the design-build process.
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Have To Say
Ready to Explore DADU or ADU Options for Your Property?
Let's discuss what's possible on your lot and whether an accessory dwelling unit makes sense for your family's future. Honest conversation, transparent process.
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The ADU Consideration: Why Now?
You might be a Seattle-area homeowner wanting parents nearby, have adult children who need affordable housing, or own a lot large enough for a DADU but feel uncertain about zoning and realistic possibilities. The barrier often isn't legal or financial. It's not knowing what works on your specific property or finding a contractor who understands the permitting workflow in your jurisdiction.
We start with a detailed site survey and an honest conversation to show you what's realistic. We'll explain costs, timelines, and whether an ADU makes sense for your family. No pressure, just clarity so you can make an informed decision about your property's potential.
How We Build ADUs Differently
Full design-build service for Seattle-area homeowners. One general contractor manages everything from site survey through completion, so nothing falls between a designer and a builder.
Site Survey & Grading
Detailed surveys reveal soil and drainage challenges upfront. We specify grading and foundation work that stands up to PNW moisture and the variable soils across the Seattle area.
Building Envelope
Flashing at every penetration, correct grade away from foundations, and waterproofing approaches matched to PNW moisture realities. Details that prevent rot five years down the line.
Permitting Expertise
We work across Seattle SDCI, King County, and Snohomish County. We know which permit reviewers expect what, how each workflow runs, and how to design for review from day one.
Design-Build Integration
One contractor from survey to completion eliminates separate architect fees. We catch setback constraints, utility complexity, and permit issues before design is locked in.
Foundation & Utilities
Separate water, sewer, and electrical feeds for detached units. Foundation piers specified for your lot's soil conditions with proper drainage integration.
Quality Inspections
Multiple inspections throughout construction, not just hoping final inspection passes, to ensure quality at every phase of your ADU build.
What Happens With Poor ADU Construction
Contractors unfamiliar with Seattle-area jurisdictions or the PNW climate create real problems:
- Foundation settling from improper grading on clay-heavy or poorly drained lots
- Moisture intrusion requiring tens of thousands in repairs
- Utility problems from lack of coordination with service providers
- Permit rejections that delay occupancy by months
- Life safety failures on egress windows and fire separation
These happen when homeowners hire the cheapest option or someone who doesn't know the jurisdiction. Our approach starts with detailed site surveys, proper grading and foundation specs, early permitting cycles, systematic code compliance, and multiple inspections throughout construction.
Why Choose Ideal Construction
We work across the Greater Seattle area, from dense urban neighborhoods in Ballard, Queen Anne, and Wallingford to the suburbs of King County and Snohomish County. Each zone has its own constraints: tight urban lots that need careful setback planning, sloped hillside lots that need engineered retaining work, mid-century suburban lots with generous footprints, and rural acreage with separate utility runs. We navigate these because we work throughout the region.
Licensed general contractors, members of the Master Builders Association of King & Snohomish Counties and AIA affiliates, we stay current on code changes and keep working relationships with permitting staff and inspectors in every jurisdiction we serve.
Serving homeowners in Seattle, Edmonds, Mountlake Terrace, Lynnwood, Mill Creek, Everett, Mukilteo, Snohomish, and Lake Stevens.
Your ADU Project: From Consultation to Completion
A transparent, step-by-step process that respects your timeline and budget
1
Initial Consultation & Site Survey
We meet at your property to discuss your goals (multigenerational living, rental income, guest space), review lot constraints, and conduct a detailed site survey. This identifies setback requirements, soil conditions, utility locations, and design opportunities. We also review the specific IRC code and zoning rules for your jurisdiction, whether Seattle SDCI, King County, or Snohomish County.
2
Design & Permitting Strategy
Our design-build team creates a detailed floor plan that maximizes your space while respecting all local regulations. We prepare permit applications, grading plans, and utility connection designs. We work across Seattle SDCI, King County, and Snohomish County, so we know which permit reviewers expect what and how each jurisdiction's review workflow runs.
3
Detailed Planning & Cost Refinement
Once design direction is set, we create detailed plans covering the building envelope, foundation pier specifications, impervious surface calculations, and egress windows for life safety. You receive a comprehensive cost estimate with line-item transparency so you understand exactly where your investment goes.
4
Permitting & Pre-Construction Preparation
We submit permits to the correct jurisdiction (SDCI, King County, or Snohomish County) and manage the approval process. Simultaneously, we prepare the site with proper grading, establish utility connections, and schedule inspections. Established relationships with local inspectors help keep timelines on track.
5
Construction & Quality Management
Your ADU or DADU is built with the attention to detail that defines our work. We manage PNW climate challenges through moisture-resistant building practices, careful foundation work, and seasonal scheduling. Regular inspections and clear communication keep you informed at every phase.
6
Completion & Occupancy
Final inspections confirm IRC code compliance and life safety requirements are met. We conduct a thorough walkthrough, address any final details, and prepare your new unit for occupancy. Your new space is ready for multigenerational living, rental income, or whatever purpose you chose.
Complementary Services
Pair ADU construction with kitchen and bathroom remodels, broader home renovations, custom home builds, or decking. Coordinating through one general contractor simplifies logistics and reduces costs.