Book a conversation with Baily. Share your address, lot dimensions, primary-home year built and footprint, tree-canopy photos, ECA overlay status (Seattle GIS), Shoreline Management Act proximity, and HOA status if any. Baily returns a rough scope, an HB 1337 applicability check (Seattle is covered), ADU vs. DADU pathway, ECA applicability, tree-protection preliminary read, and SMA proximity — in the same session.

Seattle's topography makes the ECA overlay check a first-conversation priority. Magnolia, West Seattle, Capitol Hill edges, Leschi, Madrona, Madison Park, portions of Queen Anne and Beacon Hill all frequently carry ECA overlays. Shoreline proximity adds SMA review on parcels within 200 feet of marine or lake shoreline. Tree canopy is another first-conversation question — exceptional trees on the parcel or within protection zone of the buildable area materially constrain DADU siting. Baily surfaces all four overlays at consultation — before an architect draws a line.

Schedule a pre-application conference with SDCI — land use, building, and (if applicable) geotech and tree units meet with the homeowner and designer to review preliminary plans, identify code-compliance issues, confirm permit pathway (building-permit-only vs MUP), and flag critical-areas or tree-protection applicability. Pre-app fees: $1,500-$3,500 typical. Timeline savings: 2-4 months vs. learning about issues at formal-submittal objection stage.

The SDCI pre-app conference is the most-underused cost-saver on Seattle DADU projects. A $2,500 pre-app fee that saves 3 months of carrying cost on a $400K DADU project saves meaningful capital — plus avoids the common 'first-time-DADU contractor bids from photos, hits ECA snag at permit submittal, eats 4 months of plan-review cycles' failure pattern. Baily recommends a pre-app conference on every DADU scope above the smallest backyard-cottage tier. The pre-app also surfaces neighbor-notification requirements, Landmark Board applicability on historic-eligible structures, and SEPA-categorical-exemption applicability.

The matched Seattle GC walks the property, confirms primary-home electrical panel capacity (100A vs 200A — DADU typically requires 200A service), water service tap and meter sizing, existing sewer-lateral condition, solar-exposure and tree-shade maps, existing tree inventory with DBH measurements, soil-drainage observation (critical on sloped parcels), and any concurrent URM retrofit obligations if a multi-family parcel. Fixed-fee proposal follows within 5-10 business days.

Seattle's pre-1945 housing stock on the primary-home side frequently carries 100A service that does not accommodate a DADU subfeed without upgrade. 1970s-80s stock typically carries 200A baseline but panel may be full. Tree inventory documentation at the walk avoids later SDCI tree-unit surprises. Sloped parcels (>15% grade) raise foundation-design complexity and often require geotechnical assessment even on non-ECA lots. A contractor who bids from photos misses all of this — Baily's matched GC walks every Seattle lot.

Before contract signature, verify the GC's WA L&I Contractor Registration status (active, General Contractor endorsement, no suspended or administrative actions), $12,000 bond on file, general liability insurance ($200K+ / $50K), UBI tax registration, and workers' compensation coverage. Also verify each trade subcontractor's WA L&I registration — electrical (separate WA state electrical license), plumbing (certified plumber), HVAC (applicable endorsements). Verification is per-project.

AskBaily's Wave 181-era verifier automates WA L&I lookups against the public Contractor Registration search. The card below renders a sample L&I-series registration to demonstrate receipt shape. Baily also checks L&I complaint history, prior SDCI permit record, and L&I safety-enforcement history — a pattern of unresolved complaints, bond claims, or safety citations is a material red flag that shared-lead marketplaces do not surface. WA electrical licensing is particularly strict — every trade subcontractor holds a separate WA state electrician credential that Baily verifies independently.

The architect or designer develops DADU plans that honor ECA overlays (steep slope, landslide, wetland, stream buffer), Tree Protection Ordinance mitigation requirements, and Shoreline Management Act setbacks where applicable. Geotechnical assessment ($3,500-$12,500) is ordered early on ECA parcels. Biological assessment is ordered on wetland or stream-proximate parcels. Exceptional tree inventory with mitigation plan is filed with SDCI Tree Unit.

Seattle design is a three-way optimization between footprint maximization, tree preservation, and ECA compliance. A DADU that would have been straightforward in Phoenix or Dallas is frequently constrained to a narrow buildable window in Seattle by tree-protection zones, slope setbacks, and lot-coverage caps. The architect who accepts these constraints upfront and designs within them produces submittals that pass first-time; the architect who fights the constraints designs projects that stall at SDCI review. Baily's matched designer reads the overlay stack before the first sketch.

The plan set is filed through SDCI's online portal under the applicable track: building-permit-only for conforming DADUs without MUP trigger (3-6 months typical), building-permit-plus-MUP for SEPA-triggered, design-review, or non-standard scope (6-14 months), complex permit for Landmarks Board, ECA variance, or exceptional-tree mitigation scope (12-24 months). SEPA checklist, geotech report, biological assessment, tree-protection plan, and energy-code compliance documentation all attach at submittal.

SDCI review objections on Seattle DADU submissions typically involve SEPA-categorical-exemption determination, energy-code performance-path documentation, tree-protection-zone setback encroachment, ECA geotech recommendations not fully implemented in structural design, attached-ADU fire-separation detail on existing wall assemblies, or mechanical ventilation calc missing on the performance path. The architect or designer answers objections — not the homeowner. Baily's team coordinates through the SDCI project manager on the file.

Once MUP (if required) and building permit issue, utility coordination begins. Seattle City Light coordinates the electrical service upgrade on primary-home panels requiring 200A or 400A capacity for DADU subfeed. Seattle Public Utilities coordinates water service and sewer lateral work where DADU adds fixture count. Separate water meter for DADU is optional but commonly elected for rental-metering clarity. Utility coordination adds 4-10 weeks beyond permit issue.

Seattle City Light service-upgrade scheduling is 4-10 weeks and requires a coordination permit separate from SDCI's electrical permit. SPU water-service and sewer-lateral work runs on a similar cadence. A Seattle GC who schedules utility requests at permit issuance (not at substantial completion) preserves the critical path. Puget Sound Energy coordinates gas-service work on natural-gas-incorporating DADUs — though Seattle's heat-pump-mandatory energy code has reduced gas-service requests on new DADU construction substantially.

With permit in hand, site prep begins. Framing rough-in, envelope detailing (R-49 ceiling, R-21 + R-5 wall or advanced-framed equivalent, continuous air barrier), window and door install (triple-glazed on many scopes), heat-pump HVAC rough-in, and mechanical ventilation install sequence through SDCI trade-inspection checkpoints. Mandatory blower-door test at substantial completion verifies air-barrier performance ≤3 ACH at 50 Pa. Duct-leakage test verifies distribution.

Seattle's energy code is among the strictest in the U.S., and the envelope-performance premium is real. The difference between a prescriptive-path DADU (meets code but under-performs) and a performance-path DADU with triple-glazed low-e, advanced framing, continuous exterior insulation, and verified ≤2 ACH blower-door is 25-40% lower heating load annually — material when Seattle DADU heating typically runs 3,500-6,500 kWh/year on heat-pump electrics. A modest upfront premium ($6K-$12K) pays back in 5-9 years against PSE or Seattle City Light tariffs. Baily's scoping flags envelope-performance tier at scope-lock.

Structural, framing, insulation, air-barrier blower-door, electrical, plumbing, mechanical, HVAC, and energy-code inspections clear in sequence. Seattle City Light energizes permanent service; SPU confirms water meter and sewer connection. SDCI final building inspection closes the permit. A new DADU typically receives its own Certificate of Occupancy separate from the primary home's — which supports later rental or sale.

A finaled SDCI permit plus a clean WA L&I record is what future buyers, insurers, title attorneys, and the King County Assessor all require. An open residential permit that never finals is a chronic title-search flag on Seattle real estate — unpermitted or un-finaled DADU work discovered at closing can reprice or break the deal. We close the paperwork the month the project ends, file the Tree Protection final report if exceptional-tree mitigation applied, and archive the Landmarks Certificate of Approval if one was required. Clean close-out distinguishes a finished project from a perpetually pending one.

If the DADU is intended for rental, register with the Seattle Rental Registration and Inspection Ordinance (RRIO), confirm landlord-tenant compliance, and file the rental unit with the King County Assessor for post-construction reassessment. Seattle's rent-stabilization policies apply citywide on qualifying units. King County will typically reassess the parcel at the next annual cycle — the DADU improvement value flows into property tax going forward.

Seattle's rental-registration and inspection regime (RRIO) applies to almost every rental unit in the city and requires inspection at specified intervals. A DADU rented without RRIO registration is operating outside the regulatory framework and cannot enforce rental-payment remedies cleanly. King County's post-construction reassessment is inevitable — Washington's property-tax cadence does not offer a cap comparable to California's Proposition 13, though homestead-type exemptions apply on primary residences. Baily flags RRIO and the King County reassessment timing at close-out so homeowners are not surprised.