The Full Process of Building an ADU or DADU in Seattle:
Phases, Timelines, Risks, and Quality Control
Building an ADU or DADU in Seattle is a smart way to add value, income, or space.
But success depends on understanding every step — from planning to final inspection.
Below, we break down the full construction process:

How long it takes, what to watch out for, and how to ensure quality at each stage.

Phases of Building an ADU/DADU in Seattle
  • Design & Document Preparation
    What it includes:
    • Concept & architectural design
    • Engineering (if needed)
    • Full permit application package
    Timeline: 2–4 months
    Risks:
    • Design doesn’t meet zoning or building codes
    • Issues with height, parking, or energy rules
    How We Prevent This:
    ✔️ We check zoning before design starts
    ✔️ We work with architects who know Seattle DCI inside and out
  • Obtaining Building Permits
    What it includes:
    • Submitting plans
    • City review and feedback
    • Revisions
    • Final approval
    Timeline: 2–6 months
    Risks:
    • Delays from missing documentation
    • Slow responses to city requests
    Our Approach:
    ✔️ Clear system to track revisions
    ✔️ Fast updates and city communication
    ✔️ Direct contact with inspectors
  • Site Preparation
    What it includes:
    • Clearing and grading the site
    • Demolition
    • Layot marking
    • Temporary fencing and erosion control
    Timeline: 1–3 weeks
    Risks:
    • Damage to existing underground utilities
    • Inadequate foundation site preparation
    How we avoid this:
    ✔️ Always locate utilities before digging
    ✔️ Supervise layout and erosion control setup
  • Foundation Work
    What it includes:
    • Excavation
    • Rebar placement
    • Formwork and concrete pouring
    Timeline: 2–3 weeks
    Risks:
    • Incorrect dimensions
    • Poor-quality concrete pour
    • Drainage issues
    Quality control:
    ✔️ Photo documentation and rebar inspection before concrete pour
    ✔️ On-site inspection before pouring foundation
    ✔️ We work only with trusted concrete subcontractors
  • Framing
    What it includes:
    • Wall and floor framing
    • Roof truss installation
    • Exterior wall sheathing
    Timeline: 4–6 weeks
    Risks:
    • Misaligned walls or openings
    • Structural issues from framing errors
    What We Do:
    ✔️ Strict control of framing geometry
    ✔️ Check diagonals, vertical alignment, and all key dimensions
    ✔️ Pass framing inspection before moving on to roofing
  • Roofing, Windows & Doors Installation
    What it includes:
    • Roof covering installation
    • Installing window and door units
    • Waterproofing and weatherproofing
    Timeline: 2–4 weeks
    Risks:
    • Roof leaks
    • Poor window sealing
    Our Quality Control:
    ✔️ We use only high-quality roofing and window systems
    ✔️ Take photos of all installation points and verify waterproofing
  • Rough-In Stage (Utilities)
    What it includes:
    • Electrical wiring
    • Plumbing layout
    • HVAC system (heating, ventilation, air conditioning)
    Timeline: 2–4 weeks
    Risks:
    • Incorrect layout or routing of systems
    • Code violations
    Our Quality Control:
    ✔️ We use only premium roofing and window systems
    ✔️ Document and inspect all critical sealing points
  • Insulation & Drywall
    What it includes:
    • Installing thermal insulation
    • Hanging drywall
    • Taping, mudding, and prepping walls for paint
    Timeline: 2–3 weeks
    Risks:
    • Incomplete or poorly installed insulation
    • Low-quality drywall finishing (visible seams or rough surfaces)
    Our Quality Control:
    ✔️ We use only premium roofing and window systems
    ✔️ Document and inspect all critical sealing points

  • Interior Finishes
    What it includes:
    • Painting
    • Flooring installation
    • Installing kitchen cabinetry and plumbing fixtures
    • Final electrical work and trim
    Timeline: 4–8 weeks
    Risks:
    • Damage to finished surfaces during later stages
    • Poor tile or flooring installation
    How We Prevent This:
    ✔️ Maintain a clean work environment and protect all finished surfaces
    ✔️ Conduct partial inspections after each stage
  • Landscaping & Exterior Work
    What it includes:
    • Walkways and driveways
    • Yard landscaping
    • Fence installation and small architectural features
    Timeline: 2–4 weeks
    Risks:
    • Poor water drainage planning
    • Low-quality surface finish on hardscape areas
    Our Approach:
    ✔️ Landscape design is planned in advance
    ✔️ Check slope and quality of all hardscape elements before final delivery
  • Final Inspection & Certificate of Occupancy
    What it includes:
    • Passing all final building inspections
    • Receiving the official Certificate of Occupancy (permission to move in)
    Timeline: 1–3 weeks
    Risks:
    • Incomplete work
    • Building code violations
    What We Do:
    ✔️ Complete an internal final checklist before calling for inspection
    ✔️ Test all major systems (electrical, HVAC, plumbing)
    ✔️ Support the client through full project closeout

Building a DADU in Seattle is a long-term investment — and every step matters.With the right planning, quality control, and project management, your build can be completed on time, on budget, and with confidence.

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