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# DADU Contractor in Seattle WA: How to Plan and Build a Detached ADU
Finding the right DADU contractor in Seattle starts with understanding what the project actually involves. Love Construction has built detached accessory dwelling units across King County for years, from compact backyard cottages in Ballard to full two-bedroom DADUs in Columbia City. If you're considering a detached ADU on your Seattle property, here's what the process looks like from permits to move-in.
What Is a DADU, and How Is It Different From an Attached ADU?
A DADU (Detached Accessory Dwelling Unit) is a standalone structure on your existing residential lot, separate from the primary house. An attached ADU shares a wall, foundation, or roofline with the main home. Seattle's code treats them differently in a few ways:
- • Setbacks: DADUs typically require 5 feet from side and rear lot lines in most single-family zones
- • Height: Up to 22 feet in SF 5000 zones (can reach 25 feet in some zones with a pitched roof)
- • Size: Up to 1,000 square feet of living space, depending on lot size and zoning
- • Parking: Seattle eliminated off-street parking requirements for ADUs in 2019
How Seattle's DADU Permit Process Works
Seattle's permitting process for DADUs has gotten faster in recent years, but it still involves multiple steps. Here's what to expect:
Pre-Application Research
Before you draw plans, your contractor should verify:
- • Zoning: Your lot must be in a zone that allows DADUs (most SF zones do)
- • Lot coverage: Total building footprint (house + garage + DADU) can't exceed the maximum lot coverage for your zone
- • Utilities: Sewer capacity, especially in older neighborhoods like Wallingford or Fremont where infrastructure is aging
- • Tree protection: Seattle's tree ordinance can affect where you place the structure
Design and Plan Review
Seattle requires full architectural plans for DADU construction. The city reviews for structural, mechanical, electrical, and energy code compliance. Plan review currently takes 4 to 8 weeks in most cases, though complex projects in environmentally critical areas can take longer.
Construction Timeline
A typical DADU build in Seattle takes 6 to 10 months from breaking ground to final inspection. Factors that stretch timelines include:
- • Weather delays (November through February is the slowest period)
- • Custom finishes or complex site grading
- • Utility connection scheduling with Seattle Public Utilities
- • Inspection queue times, which vary by season
How Much Does a DADU Cost in Seattle?
DADU construction costs in Seattle range from $250 to $400 per square foot for a quality build. That puts a 600-square-foot cottage at $150,000 to $240,000, and a 1,000-square-foot unit at $250,000 to $400,000.
| Component | Typical Cost Range | |---|---| | Foundation and site work | $25,000 - $50,000 | | Framing and shell | $40,000 - $80,000 | | Mechanical (HVAC, plumbing, electrical) | $35,000 - $65,000 | | Interior finishes | $30,000 - $60,000 | | Permits and fees | $8,000 - $15,000 | | Design and engineering | $10,000 - $25,000 |
Several factors push costs higher in Seattle specifically:
- • Sloped lots in neighborhoods like Queen Anne or Beacon Hill require retaining walls and engineered foundations
- • Older lots may need sewer line upgrades or new water service connections
- • Custom design versus pre-designed plans adds 10 to 20 percent in architectural fees
What to Look for in a Seattle DADU Contractor
Not every general contractor has DADU experience. The permitting, engineering, and site logistics are different from a standard remodel or addition. Ask these questions:
1. How many DADUs have you completed in Seattle? Look for at least 5 completed projects with references 2. Do you handle permitting in-house? A good DADU contractor manages the full permit process, including pre-application conferences with SDCI 3. Can you show me a project on a similar lot? Lot size, slope, and access all affect the build 4. What's your approach to utility connections? Sewer and water hookups are often the most complex part of DADU construction in Seattle 5. Do you build to passive house or high-performance standards? Seattle's energy code is already strict, but going further reduces long-term operating costs
Love Construction handles DADU and ADU projects from initial feasibility through final inspection. We work in neighborhoods across Seattle and King County, including Ballard, Wallingford, Columbia City, and Burien.
Popular DADU Designs for Seattle Lots
Seattle lots vary significantly, and the best DADU design depends on your specific property. Here are the most common configurations we build:
The Backyard Cottage (400-600 sq ft)
Ideal for standard Seattle lots (5,000+ sq ft). Studio or one-bedroom layout with full kitchen and bathroom. Works well for rental income or a home office with guest suite.
The Two-Bedroom DADU (750-1,000 sq ft)
Suits larger lots in neighborhoods like Rainier Valley, Lake City, or SeaTac. Two bedrooms plus open living area. Often built for family members or as a long-term rental property.
The Garage-Top DADU
Built above an existing or new detached garage. Maximizes lot usage by stacking living space over parking or storage. Requires structural engineering for the garage foundation.
The Accessible DADU
Single-level design with zero-step entry, wider doorways, and roll-in shower. Growing demand from homeowners planning for aging-in-place needs. Smart investment since accessibility features add minimal cost during new construction but are expensive to retrofit.
Financing a DADU in Seattle
Most homeowners finance DADUs through one of these methods:
- • Home equity line of credit (HELOC): Draws against existing home equity. Rates vary but typically lower than construction loans
- • Construction loan: Converts to a permanent mortgage after the build. Requires detailed plans and contractor bids
- • Cash-out refinance: Refinance your primary mortgage and pull equity for the DADU project
- • ADU-specific loan programs: Several lenders in the Seattle market now offer products designed for ADU construction
Why April Is a Good Time to Start Planning
Spring is when most DADU projects begin the design phase in Seattle. Starting now means:
- • Permits submitted by late spring or early summer
- • Construction begins in the dry season (July through October)
- • Enclosed before fall rains arrive
- • Interior work through winter
- • Move-in or rental listing by early 2027
Frequently Asked Questions About DADU Construction in Seattle
How long does it take to get a DADU permit in Seattle?
Plan review through SDCI currently takes 4 to 8 weeks for standard DADU projects. Add 2 to 4 weeks for revisions if the reviewer requests changes. Projects in environmentally critical areas or with complex drainage may take longer.
Can I build a DADU if I already have a garage?
Yes. You can convert the garage, build above it, or remove it and build a DADU in its place. You can also build a DADU elsewhere on the lot and keep the garage. Seattle does not require off-street parking for properties with ADUs.
Do I need to live on the property to build a DADU?
Seattle previously required owner occupancy for ADU properties, but that requirement was removed. You can build a DADU and rent both the primary home and the DADU.
What's the difference between hiring an architect and a design-build contractor?
An architect designs the DADU and you hire a separate contractor to build it. A design-build contractor handles both design and construction under one contract. Design-build is typically faster and reduces coordination issues between the designer and builder.
Can I use my DADU as a short-term rental?
Seattle allows short-term rentals (Airbnb, VRBO) in DADUs, but you must register with the city, collect applicable taxes, and follow platform-specific regulations. Long-term rentals produce steadier income and avoid the management burden.
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Ready to Build a DADU in Seattle?
Love Construction designs and builds detached ADUs across Seattle and King County. Call us at (206) 339-2718 for a free project consultation, or request an estimate online. We'll walk your property, review zoning, and give you a realistic budget before any commitments.
Ready to Start Your Project?
Contact Love Construction for a free consultation on your remodeling project.