The short answer
Architect fees in Seattle run about $5,500 to $12,400 to design a 600 square foot ADU and $4,600 to $34,500 for a 2,500 square foot new home. A 600 square foot detached ADU costs roughly $103,500 to $172,500 to build. The lot sets the limits before any design starts: steep slopes, critical areas and shoreline rules.
What architects and ADUs cost in Seattle
These figures start with national cost data and apply the Seattle cost factor of 1.15 from the U.S. Army Corps of Engineers Area Cost Factors, based on the average of Tacoma (1.07) and Puget Sound bases (1.21). Design fees and build costs are listed separately. You usually pay the architect months before a builder starts.
| Job | Seattle (typical range) | US average |
|---|---|---|
| Architect fees, ADU (600 sq ft) | $5,500–$12,400 | $4,800–$10,800 |
| Architect fees, addition (500 sq ft) | $3,450–$8,650 | $3,000–$7,500 |
| Architect fees, new home (2,500 sq ft) | $4,600–$34,500 | $4,000–$30,000 |
| 3D rendering package | $920–$3,700 | $800–$3,200 |
| Prefab ADU, 600 sq ft, built | $55,200–$110,400 | $48,000–$96,000 |
| Garage conversion ADU, 600 sq ft | $34,500–$138,000 | $30,000–$120,000 |
| Attached ADU, 600 sq ft | $86,250–$155,250 | $75,000–$135,000 |
| Detached ADU, 600 sq ft | $103,500–$172,500 | $90,000–$150,000 |
| ADU above a garage, 600 sq ft | $138,000–$345,000 | $120,000–$300,000 |
| Land survey | $460–$2,050 | $400–$1,800 |
Estimates for 2026, including labor and standard parts. Seattle prices use a construction cost factor of 1.15 (US average = 1.00) from the U.S. Army Corps of Engineers Area Cost Factors, based on drawn from Tacoma (1.07) and Puget Sound bases (1.21). Your quote depends on access, materials and the condition of the home.
The cost estimator below gives design fees and weeks to permit for your project type and ZIP code. A longer version is on the architecture cost estimator page.
The same estimator has its own page, easy to share or bookmark: Architect fee estimator.
How Seattle architects charge
According to HomeGuide's national figures, residential architects charge 5% to 20% of construction cost, $2 to $15 per square foot, or an hourly rate. The fee is usually split by phase:
| Phase | Share of the fee | What you get |
|---|---|---|
| Schematic design | 20% | Layout options, massing, early cost check |
| Design development | 10% | Materials, windows, structure and systems |
| Construction documents | The largest share | The permit set and the drawings builders price |
| Bidding | 5% | Help comparing builder bids |
| Construction administration | 25% | Site visits and answers during the build |
Lots with slopes, critical areas or shoreline frontage usually need a survey, geotechnical work and a second round of city review. That pushes the fee toward the top of each range. For how fees compare across project types, see the architecture pillar page.
What the ADU itself costs
A 600 square foot detached ADU runs about $103,500 to $172,500 built, an attached ADU $86,250 to $155,250, and a garage conversion $34,500 to $138,000. A prefab unit runs $55,200 to $110,400, and an ADU above a garage $138,000 to $345,000. A land survey adds $460 to $2,050. Our ADU design guide covers layouts and cost-saving choices.
How ADU rules work in Seattle
Seattle changed its zoning in 2025. Following the Neighborhood Residential (NR) zoning changes adopted by City Council in 2025, homeowners can now build at least four homes on every lot, according to the Seattle Office of Planning & Community Development. That shift is bigger than the ADU rules alone. It changes what an architect can propose on a standard city lot.
The pre-approved plan program
The city ran a design competition for pre-approved ADU and middle housing plans. A jury of local design and architectural experts selected 15 designs plus 5 honorable mentions from 110 submissions. The selected designs range from 1 to 6 units with 0 to 3 bedrooms, and some include single-story units with ADA accessible floorplans to support aging in place.
The city says these plans make permitting faster and more predictable for duplexes, townhomes and stacked flats. Once the plans are approved, a property owner licenses them from the designer, finalizes site-specific details, and usually receives a permit within 2 to 8 weeks depending on how many homes are included. The city expects the public to be able to use the new pre-approved plans starting January 2027, so a project filed before then still needs a custom design.
What the architect has to check first
Three things decide the design before any drawing is useful.
- Lot capacity. With four homes allowed on every NR lot, an architect may show you a duplex or stacked flats instead of a single ADU. Ask for that comparison early. It changes the budget.
- Critical areas. State law defines five types: wetlands, critical aquifer recharge areas, fish and wildlife habitat conservation areas, frequently flooded areas, and geologically hazardous areas such as landslide, erosion and seismic hazard areas. Permit applicants are responsible for locating and disclosing critical areas and their buffers on the site.
- Jurisdiction. Seattle, Bellevue, Redmond, Kirkland, Tacoma, Everett and Renton each run their own building department. Unincorporated King County is handled by King County Permits, which serves only unincorporated areas. Check jurisdiction and zoning before you apply.
Hillside, shoreline and critical area lots
King County's updated Critical Areas Ordinance takes effect February 18, 2026, except regulations for critical areas within shoreline jurisdiction. The shoreline-related regulations take effect 14 days after review and approval by the Washington State Department of Ecology. The county adopted the update on December 2, 2025, and it expands buffers around certain critical areas in unincorporated King County.
The shoreline jurisdiction includes all shorelines, shorelands and the 100-year floodplain. If your lot touches Puget Sound, Lake Washington, a major creek or the floodplain, expect a shoreline review on top of the building permit.
For most critical areas, location, extent and classification are determined by the county based on a site-specific critical area report by an ecological or geological professional. The county's iMap tool shows general locations of some critical areas but is not suitable for determining exact location and classification. In Pierce County, a Level 1 Pre-Application Screening is required for projects with critical area indicators, special site restrictions, or properties served by on-site septic systems or private wells. Everett's new critical area regulations take effect June 1, 2026 and affect applications received after that date.
A steep lot usually means a geotechnical report, a foundation designed by an engineer, and a longer plan review. Budget for those before you sign a design contract.
Do you need a permit?
Yes, for any ADU, addition or new home. Each city runs its own process:
| City | How to apply | Notes |
|---|---|---|
| Seattle | Seattle Department of Construction and Inspections | Pre-approved plans expected January 2027 |
| Bellevue | MyBuildingPermit.com | Predevelopment Services Review available before you file |
| Redmond | City permit center, 15670 NE 85th St | Sprinklers required for new homes and detached ADUs |
| Tacoma | Tacoma Permits (Accela) | Account required |
| Everett | Online Permitting Portal | Residential submittal checklist required with the application |
| Renton | Online Permit Portal | Free ADU model base plans through the PRADU Program |
| Unincorporated King County | MyBuildingPermit.com | County permits only for unincorporated areas |
Bellevue's process runs application, plan review, contractor approval and inspections. The city offers a Predevelopment Services Review to get feedback before you submit. Redmond requires a building permit for new homes, additions, remodels, ADUs, garage conversions and accessory structures. It also requires sprinklers for new homes and detached ADU units. Renton offers free ADU model base plans to residential property owners through its Permit Ready ADU Program. The program streamlines application and review. Pierce County publishes estimated permit costs based on current fees. It also offers predesigned project guides for decks and detached structures that need no engineer or architect.
The 2024 Washington State Building Codes implementation has been delayed until May 3, 2027, according to Everett. Ask your architect which code edition will apply to your application.
A complete set also needs energy code documents. Our guide to permit drawings lists what a complete set includes.
Structural engineering in Seattle
Many projects here need a structural engineer: steep-slope foundations, second stories, ADUs above garages, and anything with a retaining wall. HomeGuide puts structural plans at $500 to $3,000 for an average house or remodel, and most engineers will not stamp plans they did not create or supervise. Our guide to structural coordination explains how the engineer's drawings fit into the architect's set. If you want to see the unit from the main house or the street before the layout is fixed, ask about 3D renderings.
How to check an architect before you hire
Washington architects are licensed by the Washington State Department of Licensing. Under Chapter 18.08 RCW, it is unlawful to practice or offer to practice architecture in the state, or to use a title including the word "architect," unless the person is registered or authorized under that chapter.
- Look up the individual and the firm on the Department of Licensing's Look up a business or professional license page.
- Confirm the firm holds a certificate of authorization. A business entity must hold one from the director to practice architecture in Washington.
- Ask about the architect's continuing education. To maintain a license, architects must complete 24 professional development hours within their 2-year license period.
- Get a written contract before work starts, with the scope, fee, schedule and who owns the drawings.
- Ask who will draw the structural sheets and the energy code documents.
An architect registered in another state may offer to practice in Washington only if the offer clearly and prominently states they are not registered here, and they must register before practicing or signing a contract. A person with an accredited architectural degree may use the title "architectural associate" while enrolled in a board-recognized training program under direct architect supervision.
Washington's definition of the practice of architecture is broad. It includes predesign services, schematic design, design development, preparation of construction contract documents, and administration of the construction contract, including alterations or additions to structures. Administration means periodic observation of materials and work for general compliance with the contract documents. It does not include responsibility for supervising construction methods, site conditions, equipment, personnel or worksite safety. Site safety stays with the builder.
If you are also hiring a general contractor, check the registration under Chapter 18.27 RCW. Contractors must be registered with the state, must carry a bond and insurance, and must give you a disclosure statement. Our vetting process guide explains how GOLDGCP checks both.
Areas we cover
GOLDGCP architects and vetted pros work across the Seattle metro, including:
- Seattle, including lots near Lake Washington and Puget Sound
- Bellevue
- Redmond
- Kirkland
- Tacoma
- Everett
- Renton
Each city runs its own building department and ADU rules. Unincorporated King County is permitted separately. Enter your ZIP code to see local prices.
How GOLDGCP works
- Tell us about the lot and the project.
- Our in-house architects check zoning, ADU capacity, critical areas and shoreline status, then draw the permit set.
- We match you with up to 3 vetted, licensed builders and show prices by ZIP code.
- You approve each stage and release milestone payments, tracked in the client portal. See payment protection for how milestones work.
Builders pass six-step vetting first: state license verification, an insurance check, a business and public-records check, portfolio review, client reference calls, and onboarding with a quality score.
Frequently asked questions
How much does an architect cost in Seattle?
About $5,500 to $12,400 for a 600 square foot ADU design, $3,450 to $8,650 for a 500 square foot addition, and $4,600 to $34,500 for a 2,500 square foot new home. These use national data at Seattle's 1.15 cost factor.
How much does it cost to build an ADU in Seattle?
A 600 square foot detached ADU runs about $103,500 to $172,500 built, an attached ADU $86,250 to $155,250, and a garage conversion $34,500 to $138,000. A prefab unit runs $55,200 to $110,400. Design, survey and permit fees are extra.
What is Seattle's pre-approved ADU plan program?
The city selected 15 pre-approved ADU and middle housing designs plus 5 honorable mentions from 110 submissions. You license a plan from its designer, finalize site details, and usually get a permit in 2 to 8 weeks. The plans are expected to be available starting January 2027.
How many homes can I build on a Seattle lot?
Following the 2025 Neighborhood Residential zoning changes, homeowners can build at least four homes on every lot. That opens options beyond a single ADU, such as duplexes, townhomes and stacked flats. Ask your architect to compare the options before you settle on a design.
Do I need an architect for an ADU in Seattle?
Not always. Washington licenses architects and protects the title, but small residential work can often be drawn by a designer. Anything with structural complexity, a steep slope or a critical area should have a licensed architect or engineer involved. Ask who stamps the drawings.
How long does a Seattle ADU permit take?
The city says pre-approved plans usually permit within 2 to 8 weeks depending on the number of homes. Custom designs take longer because of plan review and any critical area or shoreline review. Ask your architect for the current review time for your project type.
What changes on a hillside or shoreline lot?
Critical areas rules add reports and buffers. King County's updated Critical Areas Ordinance takes effect February 18, 2026, and the shoreline jurisdiction includes all shorelines, shorelands and the 100-year floodplain. Expect a site-specific report by an ecological or geological professional and a longer review.
How we calculate these prices
GOLDGCP starts from national price ranges for each job, taken from published 2026 cost guides and checked against local price guides where they exist. To get a local price, we multiply the national range by the construction cost factor for the metro from the U.S. Army Corps of Engineers Area Cost Factors (US average = 1.00). Where that table has no entry for a metro, we use the nearest listed location or the state value. For ZIP codes outside the 50 largest metros, the cost estimator uses the state's price level from the Bureau of Economic Analysis Regional Price Parities. Ranges include labor and standard materials but not unusual site conditions, so a written quote after an inspection is always the final price.
Sources
- Washington State Department of Licensing · Washington State Department of Licensing
- dailyplanit.seattle.gov
- King County, Washington
- Washington State Department of Licensing · Washington State Department of Licensing
- U.S. Army Corps of Engineers
- U.S. Bureau of Economic Analysis
About this guide
Written by the GOLDGCP editorial team. Prices come from national cost guides adjusted with official construction cost factors for Seattle; rules and statistics come from the agencies and reports linked in the text. We update this page when prices or codes change.
