14 Best ADU Builders in Seattle – 2026

If you researched Seattle ADU rules more than a year ago, some of what you learned is now wrong. The City updated its ADU regulations in 2025, with additional residential changes taking effect in 2026, and the revisions touched the details homeowners plan around: how many units are allowed and in what combination, the size formula, how height is measured, and whether parking is required. Guidance still circulating online frequently reflects the older framework.

For those interested in residential real estate exposure without a construction project, Ark7 offers fractional interests in professionally managed rental-property series, with shares starting as low as $20, subject to offering availability and eligibility.

This guide covers 14 ADU builders and service providers across Seattle and King County, grouped by service type rather than ranked. Most pricing, review, and volume figures are company-reported, so verify contractor licensing through Washington Labor & Industries before signing.

Key Takeaways

• Seattle generally allows up to two ADUs on a lot with a principal dwelling. The ADUs may be attached, detached, or a combination, so two detached units can be permitted.
• Seattle does not require off-street motor-vehicle parking for ADUs in any area or zone.
• Seattle generally limits an ADU to 1,000 square feet of gross floor area, subject to specified exclusions and other development standards.
• Permitted ADU height is tied to the height permitted for a principal dwelling unit under the applicable zoning rather than a fixed figure.
• No owner-occupancy requirement has applied since Seattle’s 2019 reforms.
• Pre-approved ADU plans can produce permits in roughly 2 to 6 weeks in most qualifying, uncomplicated cases.
• Ark7 offers shares in rental-property series starting as low as $20, subject to offering availability and eligibility.

How This List Was Compiled

This list was assembled from publicly available company information rather than a scoring model, and companies are grouped by service type rather than ranked. Two entries are separated deliberately: one is an architecture firm providing design and permitting rather than construction, and one is a referral service whose own terms state it connects homeowners with independent contractors and does not perform or guarantee work. Pricing, review counts, and volume claims are company-reported and labeled as such, with ratings current as of August 2026.

Seattle ADU Rules to Understand First

• Number and type: Seattle generally allows up to two ADUs in addition to the principal dwelling. Either or both may be attached or detached.
• Size: ADUs are generally limited to 1,000 square feet of gross floor area, subject to specified exclusions.
• Height: Permitted height is tied to the height permitted for a principal dwelling unit under the applicable zoning. Confirm current development standards with SDCI.
• Parking: Seattle does not require off-street motor-vehicle parking for ADUs in any area or zone.
• Setbacks: These depend on zoning and lot configuration. In Neighborhood Residential zones, ADU setbacks can generally be 5 feet, with a 0-foot condition available where the setback abuts an alley.
• Owner-occupancy: No requirement since Seattle’s 2019 reforms.
• Short-term rental: Seattle defines a short-term rental as a dwelling rented for fewer than 30 consecutive nights and requires operator and unit licensing. Most operators may operate two units: their primary residence and one secondary unit in which they do not live.

14 ADU Companies and Service Providers Operating in Seattle for 2026

1. Seattle ADU Inc (Fixed-Price Design-Build)

Address: 509 Olive Way, Seattle, WA 98101

Phone: (206) 210-3411

License: WA #SEATTI*752N6

Hours: Mon to Fri 8 AM to 6 PM PT, Sat by appointment

Rating: Company reports a 5.0 average across 441+ reviews spanning multiple platforms including BuildZoom, Houzz, Networx, Porch, Thumbtack, and Yelp

Price Range: DADUs from $450K, garage conversions from $200K, attached ADUs from $300K

What Sets Seattle ADU Inc Apart:

• Design-build ADU and DADU construction with fixed-price contracts
• Full SDCI permit handling
• Published starting prices across all three ADU types
• Central downtown location

2. Seattle Modern Buildings (High Volume)

Phone: (206) 840-8356

Type: Design-Build

Price Range: 1,000 sqft DADU from $320K

Warranty: Company-stated three-year coverage

Rating: Company-reported 4.8/5 across 30+ Google reviews

The company reports building 70+ homes per year with more than 10 years in Seattle. These are company-reported figures.

What Sets It Apart:

• Detached ADUs, duplexes, and modern homes
• Published DADU starting price at the lower end of the Seattle market
• Three-year warranty coverage

3. Kolmo Construction (Project Management Credentials)

Phone: (206) 410-5100

Type: ADU and Remodeling Contractor

Price Range: $100K to $300K+ depending on scope

Experience: Company-reported 12+ years of Seattle-area construction

What Sets It Apart:

• PMP-certified project management
• ADU construction alongside residential remodeling
• Wide scope range accommodating conversions and new builds

4. Haas Development & Construction (Pre-Approved Plans)

Address: 4001 Aurora Ave N, Seattle, WA 98103

Phone: (206) 494-3369

Type: Prefab and Custom ADU

Haas offers prefab and custom ADU solutions with pre-approved DADU plans. Seattle’s pre-approved plan program can produce permits in roughly 2 to 6 weeks in most qualifying, uncomplicated cases.

What Sets It Apart:

• Pre-approved DADU plan library
• Both prefab and custom delivery
• North Seattle location

5. Seattle ADU Builders (City-Limits Focus)

Address: 4138 Baker Ave NW, Seattle, WA 98107

Phone: (206) 222-2898

Hours: Mon to Fri 8 AM to 5 PM

Price Range: Detached ADUs from $450K

What Sets It Apart:

• Works exclusively inside Seattle city limits
• Free feasibility study
• Same-day response and a dedicated permit specialist

6. Ballard Backyard Cottages (Multiple Delivery Options)

Phone: (206) 612-6657

Type: DADU Specialist

What Sets It Apart:

• Pre-fab cabins, custom DADUs, and ADU conversions
• Pre-approved plan options
• Emphasis on streamlined processes

7. LYD Construction (Small-Volume Contractor)

Location: Seattle, WA

Type: General Contractor

Rating: 5.0/5 across 16 Houzz reviews

What Sets It Apart:

• ADU construction alongside general contracting
• Consistent Houzz review scores across a smaller sample
• Seattle-based operation

8. Love Construction (Passive House Certified)

Address: 17025 33rd Ave S, SeaTac, WA 98188

Phone: (206) 339-2718

License: WA #LOVECC*802N4

Price Range: Attached ADUs $85K to $280K, DADUs $175K to $550K

Service Area: SeaTac, Seattle, Renton, Burien, Bellevue, Kirkland

A passive-house certified builder focused on high-performance construction. Passive-house construction can substantially reduce building energy demand, particularly heating and cooling loads, though actual savings depend on the certification standard, building, climate, occupancy, and energy prices.

What Sets It Apart:

• Passive house certification
• Widest published price range in this guide, spanning attached and detached
• South King County base with broad Eastside coverage

9. Giant Builders Seattle (Cost Calculator)

Phone: (425) 757-7872

Type: Design-Build

Price Range: $300K to $600K+ for DADU, $200K to $400K attached, $80K to $250K conversions

Cost per sq ft: $400 to $650 all-in for DADU

Hours: Mon to Sat

What Sets It Apart:

• Published ADU cost calculator
• Coverage across new DADU construction and conversions
• Saturday availability

10. MNBE Construction & Development (Tri-County)

Service Area: King, Snohomish, and Pierce counties

Type: Custom Home and ADU Builder

Hours: Mon to Sat

What Sets It Apart:

• Detached and attached ADUs alongside custom home construction
• Quick phone assessments for project viability
• Three-county coverage

11. Anyvision Home Remodeling (Eastside Design-Build)

Address: 8709 161st Ave NE, Unit 377, Redmond, WA 98052

Type: Licensed Design-Build Contractor

Rating: 5.0/5 across 73 Houzz reviews

Service Area: Greater Seattle area

What Sets It Apart:

• Large Houzz review sample at a perfect score
• Home remodeling alongside ADU construction
• Redmond base serving the Eastside

12. West Coast Homes (Tiny and Modular)

Type: Tiny Home, Park Model, and Modular Builder

Price Range: Tiny homes from $120K, park models from $135K, modular homes from $185K

What Sets It Apart:

• Lowest published entry pricing in this guide
• Three product categories at distinct price points
• Builds ADUs alongside tiny and park model homes

ADU Architects and Design Firms

These firms provide design and permitting rather than construction, so you would contract separately with a licensed builder.

13. Piper Cole Architects (Design and Permitting)

Location: Kirkland, WA, serving greater Seattle

Type: Architecture Firm

Phone: (425) 753-6452

Service: ADU design, permitting, architectural drawings, and SDCI compliance

An architecture firm offering ADU and residential design, serving the Seattle metro since 2000.

What Sets It Apart:

• Free initial consultation
• SDCI compliance focus
• More than two decades serving the Seattle metro

Contractor-Matching Services

This is a referral service rather than a builder. Its own terms state that it connects homeowners with independent contractors and does not perform or guarantee any work.

14. Greater Seattle Remodeling (Referral Service)

Address: 1850 130th Ave NE #1, Bellevue, WA 98005

Phone: (206) 203-5120

Service: Connects homeowners with vetted contractors

Price Range: Projects from $150K

What Sets It Apart:

• Contractor-matching concierge model
• Bellevue base serving the Eastside
• Verify the licensing, insurance, and track record of any contractor matched through a referral service, since the service itself does not stand behind the work

How to Choose the Right ADU Builder

• By service type: Twelve entries here build, one designs and permits, and one refers. Confirm which you are hiring before signing anything.
• By published price point: Entry pricing spans from $80K for conversions and $120K for tiny homes to $450K and above for detached construction. Compare what each figure includes.
• By performance priority: Love Construction focuses on passive house certification, while others emphasize speed, volume, or fixed pricing.
• By coverage: Central Seattle is served by Seattle ADU Inc, Ballard, and Seattle ADU Builders; North Seattle by Haas; South King County by Love Construction; the Eastside by Anyvision and Piper Cole; and the tri-county area by MNBE.

Questions to Ask Any Seattle ADU Builder

• Do you build, design, or refer? Which contract am I signing?
• What is your experience with SDCI permitting specifically, and do you have pre-approved plans available?
• Under current rules, how many ADUs and what combination does my lot support?
• Does your quoted price reflect the 1,000 square foot gross floor area limit and applicable exclusions?
• Is your published review count from a single platform or aggregated across several?
• Is your Washington L&I registration active, and what warranty coverage do you provide?

Financing an ADU in Seattle

• Home Equity Line of Credit: A common option using existing home equity.
• Construction loans: Short-term financing converted to permanent mortgage upon completion.
• Personal loans: Suitable for smaller conversion projects.
• Cash investment: Eliminates interest costs but ties up capital.
• Property tax exemption: Certain qualifying home improvements, including ADU construction, may receive a temporary Washington property-tax exemption subject to RCW 84.36.400’s valuation, filing, and eligibility requirements. The general exemption applies for three assessment years only to the extent the improvement represents 30% or less of the value of the original structure, the taxpayer must file notice before the improvement is made, and it generally cannot be claimed more than once in five years. Confirm eligibility with the King County Assessor before construction.
• Permit and utility budgeting: Seattle calculates fees under its Fee Subtitle and permit-fee estimator, and SDCI notes that most fees increased in 2026. Use the current estimator for project-specific figures rather than a general range.

Comparing ADUs and Fractional Real Estate

Building an ADU can create rental-income potential and may affect a property’s market value, though the amount varies substantially by neighborhood, unit characteristics, condition, legal status, and rental economics. It also requires substantial capital and ongoing landlord responsibilities.

ADU considerations:

• Illustrative monthly rent ranges run roughly $1,600 to $2,000 for a studio, $2,000 to $2,500 for a one-bedroom, and $2,500 to $3,200 for a two-bedroom. These are illustrative rather than a measured citywide dataset.
• Build any projection from current comparable listings in your immediate area, noting the month of measurement.
• Net income depends on assumptions a headline figure does not fix, including vacancy, repairs, insurance, the property-tax impact, utilities, management, capital expenditures, and financing.
• Because a simple rent-divided-by-cost calculation models no financing, any resulting figure is an unlevered yield on project cost rather than a cash-on-cash return.
• King County provides parcel-specific assessment data rather than a universal uplift figure, so consult a local appraiser rather than assuming a fixed increase.

How fractional investing compares:

For those who prefer fractional real estate exposure rather than developing and managing an ADU directly, Ark7 is another model to consider:

• Shares in rental-property series starting at $20 per share, subject to offering availability and eligibility
• Cash distributions when available, subject to property performance, expenses, reserves, and offering terms
• Professional property selection and management
• Exposure across multiple markets rather than a single local property
• No construction timelines or permitting to manage
• Potential access to secondary trading, subject to holding periods, legal and state restrictions, platform availability, and market liquidity. Liquidity is not guaranteed.
• Ark7 IRA options allow retirement funds to be invested in fractional rental-property series, subject to IRA rules, custodian fees, and individual circumstances

These are speculative securities involving substantial risk, including illiquidity, lack of diversification, and complete loss of capital.

Conclusion

Seattle’s ADU rules changed in 2025 and 2026, and much of the guidance circulating online still reflects the older framework. The number and type of units permitted, the size formula, height limits, and parking requirements have all shifted, which makes verifying current standards for your specific parcel the necessary first step.

Why Seattle Stands Out for ADU Projects

• Two-unit allowance: Up to two ADUs alongside a principal dwelling, in any attached or detached combination.
• No parking mandate: Seattle does not require off-street parking for ADUs in any zone.
• No owner-occupancy rule: Removed in Seattle’s 2019 reforms.
• Pre-approved plan program: Qualifying uncomplicated projects can permit in roughly 2 to 6 weeks.
• Deep provider market: Design-build contractors, architects, passive-house specialists, and modular builders all operate locally.

Investor Tips for Seattle ADU Projects

Confirm current SDCI standards for your parcel before commissioning design, since size, height, and setback rules have changed recently. Verify contractor registration through Washington L&I using the exact legal business name, and ask whether a company builds or only refers. Check whether a published review count is from one platform or aggregated across several. When modeling returns, separate gross rent from net income and state your vacancy, maintenance, insurance, tax, and management assumptions explicitly. Confirm any property-tax exemption eligibility with the King County Assessor before construction begins, since the notice must be filed before the improvement is made.

For those who prefer residential real estate exposure without a construction project, Ark7 offers shares in rental-property series starting at $20, subject to offering availability and eligibility.

Frequently Asked Questions

How many ADUs can I actually build on my Seattle lot?

Seattle generally allows up to two ADUs in addition to the principal dwelling, and either or both may be attached or detached. That means two detached units can be permitted, which was not the case under the older framework many online summaries still describe. Each unit is generally limited to 1,000 square feet of gross floor area, subject to specified exclusions and other applicable development standards. Confirm current standards with SDCI for your specific parcel.

Do I need to provide parking for an ADU in Seattle?

No. Seattle does not require off-street motor-vehicle parking for ADUs in any area or zone. Older guidance describing a quarter-mile transit proximity test no longer reflects the current code, so disregard summaries that condition the exemption on distance to a transit stop.

Can I run my ADU as a short-term rental?

Seattle defines a short-term rental as a dwelling rented for fewer than 30 consecutive nights and requires operator and unit licensing. Most operators may operate two units: their primary residence and one secondary unit in which they do not live, and the primary residence itself can be an attached or detached ADU. Rules and licensing requirements change, so confirm current requirements with Seattle Business Regulations before planning around short-term rental income.

Is there a property tax break for building an ADU?

There can be, but it is narrower than commonly described. Certain qualifying home improvements, including ADU construction, may receive a temporary Washington property-tax exemption subject to RCW 84.36.400’s valuation, filing, and eligibility requirements. The general home-improvement exemption applies for three assessment years only to the extent the qualifying improvement represents 30% or less of the value of the original structure. The taxpayer must file the required notice before the improvement is made, and the exemption generally cannot be claimed more than once in five years. Confirm eligibility with the King County Assessor before construction.

Do I need separate utilities for my ADU?

Requirements vary by project type. Detached ADUs typically need separate electrical service and may require independent water and sewer connections, which adds meaningfully to project cost. Attached ADUs and conversions can sometimes share utilities with the main house, though separate metering is often preferred for rental situations to track tenant usage. Confirm requirements with the relevant utilities for your specific parcel.

Neither Ark7 nor Ark7 Properties is a broker-dealer or an investment adviser. Dalmore Group LLC, a registered broker-dealer and member FINRA/SIPC, located at 525 Green Place, Woodmere, NY 11598, is the broker-dealer of record for Ark7, an issuer direct offering. Neither Ark7 nor Dalmore makes recommendations or provides advice about investments, and nothing here should be construed as a recommendation for any security. An investment in an offering constitutes an investment in a particular series and not in Ark7 or any of the underlying assets. Investments on the Ark7 platform are speculative and involve substantial risks, including illiquidity, lack of diversification, and complete loss of capital. Cash distributions are not guaranteed and are subject to property performance, expenses, reserves, and offering terms. Past performance is no guarantee of future results. This article is for informational purposes only.