Seattle is the largest ADU market in the Puget Sound region, and the city has actively encouraged backyard cottages through its pre-approved DADU plan program and permit reforms. Building permits are issued by the Seattle Department of Construction & Inspections (SDCI), and under Washington's HB 1337 most residential lots can now add an accessory dwelling unit with no owner-occupancy requirement. Whether you're converting a basement or building a detached backyard cottage, the builders below focus on Seattle's permitting process and lot conditions.

DIGS Construction

Seattle, WA
★★★★★ 5 (8 reviews)

Specializes in ADU and DADU construction in Seattle and surrounding areas. Custom designs, transparent pricing, sustainable building practices.

Detached ADU (DADU) Attached ADU Custom Design

Era Builders

Seattle, WA
★★★★★ 5 (10 reviews)

Premier DADU construction contractor in Seattle. Handles all permitting needs. Innovative design solutions and expert construction team.

Detached ADU (DADU) Attached ADU Kitchen/Bathroom Remodel

J & M Remodel

Seattle, WA
★★★★★ 5 (38 reviews)

Custom ADU specialists serving Seattle, Bellevue, and greater Puget Sound. Full-service from design to permitting to construction. Free estimates available.

Detached ADU Attached ADU Backyard Cottage

LYD Construction

Seattle, WA
★★★★★ 5 (51 reviews)

Full home remodeling contractor with ADU specialization. Covers wide service area across Greater Seattle and Eastside.

Detached ADU Attached ADU Garage Conversion Basement ADU

Raincap Construction

Seattle, WA
★★★★★ 5 (19 reviews)

Established 2007. Experienced in custom remodeling and ADU/DADU construction. 6-9 month average timeline. Specializes in all architectural styles.

Detached ADU (DADU) Attached ADU Garage Conversion

Seattle Backyard Homes

Seattle, WA
★★★★★ 5 (6 reviews)

Premier ADU builder serving Seattle area and beyond. In-house design team. Sustainable design options. Full permitting and construction management.

Detached ADU Attached ADU In-Law Suite Garage Conversion Custom Design

Haas Development & Construction (Urban Cottage)

Seattle, WA

Exclusive custom contractor for all Urban Cottage ADU/DADU projects. Full permit-to-build service. Expert guidance on ADU regulations.

Detached ADU Attached ADU

SKYDADU

Seattle, WA

Comprehensive DADU service integrating financing, building, and management. Offers PDF booklet resource on ADU planning. Award-winning quality.

Detached ADU (DADU) Prefab

ADU FAQs for Seattle

Do I need to live on my property to build an ADU in Seattle?

No. Washington's HB 1337 eliminated owner-occupancy requirements statewide, so Seattle homeowners can build a detached DADU or an attached ADU and rent out either the main house or the accessory unit. Seattle also offers pre-approved DADU plans that can shorten the permitting timeline.

Who issues ADU permits in Seattle?

ADU and DADU permits in Seattle are issued by the Seattle Department of Construction & Inspections (SDCI). Most projects require a construction permit, and detached units may also need site and utility review depending on lot conditions.

How much does it cost to build an ADU in Seattle?

Costs vary widely by size, type (attached vs. detached), and site conditions such as sewer connections and slope. See our Washington ADU cost guide for current ranges, then request free quotes from the Seattle builders above to compare bids.

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