DADU Electrical Cost Seattle & Auburn 2026

Detached accessory dwelling units — DADUs, backyard cottages, in-law suites — have become one of the most common electrical projects we take on across King, Pierce, and Thurston counties. Seattle loosened its DADU rules in 2020, and construction has been accelerating ever since. Auburn, Renton, and most South Sound cities now allow them too. If you are planning a DADU, the electrical work is one of the bigger decisions you will make. This guide covers what is actually involved, what it costs in 2026, and the most common mistakes people make when they skip a qualified electrician.

Modern DADU exterior with dark metal corrugated siding — Seattle-style detached accessory dwelling unit — This style of dark-clad modern cottage is one of the most common DADUs we wire across Seattle, Auburn, and the South Sound.

What Makes DADU Electrical Different from a Regular Home Addition

A DADU is treated as a separate dwelling unit under the electrical code — not an addition to your house. That distinction matters in several ways:

Separate electrical service. Your DADU typically gets its own meter, its own panel, and its own service entrance. Seattle City Light, PSE, and Tacoma Power each have their own process for setting up a new meter on a property that already has one.
New service size. Most DADUs are wired with a 100-amp or 125-amp service. If you plan to add an EV charger, electric heat, or a mini-split, plan for 125A or 200A from the start.
Trenching and underground conduit. On most Seattle and South Sound lots, reaching the DADU means trenching across your yard. Concrete driveways, mature trees, and tight lot lines all complicate this step.
Full permit and inspection. DADU electrical work requires a permit from your local AHJ — Seattle DCI, the City of Auburn, or your county. We pull the permit and handle inspection coordination on every job.

Dark cedar barn-style DADU — typical Pacific Northwest detached backyard cottage in Seattle area

DADU Electrical Cost in Seattle and the South Sound in 2026

Full DADU electrical rough and finish: $15,000 to $20,000+ depending on square footage, service size, and trenching distance
Underground service lateral (trenching, conduit, wire): $2,500 to $6,000
Panel and service entrance only: $3,500 to $5,500
EV charger add-on: $800 to $1,800

Black modern fiber cement DADU exterior with large windows — contemporary Seattle backyard cottage — Dark fiber cement and modern window layouts are a signature of 2025–2026 DADU builds in Seattle and South King County.

The Step-by-Step DADU Electrical Process

Site walkthrough and load calculation — we assess your panel capacity, measure the trench path, and calculate your load.
Permit application — Seattle DCI, City of Auburn, or your county building department. Typically 2 to 6 weeks in Seattle, faster in South Sound cities.
Trenching and underground conduit — coordinated with your GC or directly with you.
Utility coordination — we contact PSE, Seattle City Light, or Tacoma Power to schedule the meter set.
Rough-in wiring — outlets, lights, bath fans, kitchen circuits, EV charger rough-in, HVAC connections.
Rough-in inspection — required before drywall goes up.
Panel set and service connection — after rough-in approval, we set the panel and coordinate the final meter set.
Finish wiring and final inspection — devices, fixtures, covers installed. Signed-off permit at the end.

Underground electrical conduit being installed — required for running power from main house to DADU — Underground conduit like this runs from your main service to the DADU. Trenching across a typical Seattle or Auburn lot adds $2,500–$6,000 to the project.

Common DADU Electrical Mistakes to Avoid

Undersizing the panel. For a 2026 DADU with a mini-split, EV charger, and modern appliances, plan for at least 100A, preferably 125A.
Skipping the separate meter. Sharing your home’s meter creates billing conflicts and can violate utility rules.
Not budgeting for the trench. The underground service lateral is a real cost — get it quoted early.
Starting without a permit. Unpermitted DADU electrical is a major liability when you sell or rent. We do not do unpermitted work.
Not verifying your electrician’s license. Check at secure.lni.wa.gov/verify. Le Bros holds WA L&I license #LEBROBC755MT.

Residential circuit breaker panel showing multiple breakers — DADU electrical panel sizing matters for modern loads — For a 2026 DADU with a mini-split, EV charger rough-in, and standard appliances, plan for at least 100A — preferably 125A or 200A from the start.

DADU Rules by City

Seattle: Permit through Seattle DCI. Seattle City Light handles the meter set. Most lots allow DADUs by right. Code follows Washington State electrical code with local amendments.

Auburn: Permit through City of Auburn Community Development. PSE handles service. Auburn is more permissive on lot coverage than Seattle.

Renton, Kent, Federal Way: Permit through respective city building departments. PSE is the utility. Permit turn times are generally faster than Seattle.

Tacoma: Tacoma Power handles service. Permits through Tacoma Community Development.

A detached accessory dwelling unit (DADU) — separate structure on a residential property requiring its own electrical service — Each DADU is treated as a separate dwelling under electrical code — separate service, separate panel, and in most cases a separate meter.

Frequently Asked Questions: DADU Electrical

Does a DADU need its own electrical panel?

Yes. A DADU is a separate dwelling unit and requires its own panel and, in most cases, its own meter. This keeps utility billing separate and meets code requirements for a habitable unit.

How much does DADU electrical cost in Seattle in 2026?

Full DADU electrical rough and finish for a new build typically runs $8,000 to $18,000. Underground trenching adds $2,500 to $6,000.

Do I need a permit for DADU electrical work in Seattle or Auburn?

Yes. All DADU electrical work requires a permit and inspection. Le Bros pulls the permit and handles inspection coordination on every job.

How long does DADU electrical take?

On-site work typically takes 3 to 5 days spread across the build schedule. Permits add 2 to 6 weeks. Utility meter scheduling adds 1 to 3 weeks at the end.

Can I add an EV charger to my DADU?

Yes — plan for it from the start. Adding EV charger rough-in during the build costs far less than returning later. Most DADU panels we install support a Level 2 charger without upgrades.

Ready to Get Started?

Le Bros Construction offers comprehensive DADU electrical services across Seattle, Auburn, Tacoma, Renton, Federal Way, Gig Harbor, Olympia, and the greater Puget Sound area. Loi Le is a Washington State master electrician with 20+ years of experience in residential, commercial, and new construction wiring.

WA L&I license #LEBROBC755MT. Full liability insurance and workers’ comp. We pull every permit and walk every inspection.

Call 206-850-8293 or request a free site walkthrough.

DADU Electrical in Seattle & Auburn: What It Costs in 2026