DADU Permit Fees in King County: A Complete Breakdown

DADU Permit Fees: $43,000–$81,000

Permit fees are one of the largest soft costs in any DADU project — and one of the least understood. King County homeowners are often surprised to learn that permits, impact fees, and utility connections can total $43,000 to $81,000 before construction even begins. Understanding each fee category helps you budget accurately and avoid sticker shock at the permit counter.

This breakdown covers fees for unincorporated King County. Incorporated cities like Seattle, Bellevue, and Kirkland have their own fee structures — sometimes higher, sometimes lower.

Building Permit Fees: $15,000–$35,000

The building permit fee is calculated based on the project’s estimated valuation — the total cost of construction as determined by King County’s valuation tables.

How It’s Calculated

• King County uses ICC (International Code Council) building valuation data tables
• The per-square-foot value is multiplied by your DADU’s size
• The fee is a percentage of this calculated valuation
• Fees increased 12–19% in 2025 due to rising construction costs in the valuation tables

Typical Range

• 500 sq ft DADU: $12,000–$20,000
• 800 sq ft DADU: $18,000–$28,000
• 1,000 sq ft DADU: $22,000–$35,000

Impact Fees: $15,000–$30,000

Impact fees fund public infrastructure improvements needed to serve new development. King County assesses multiple impact fees for new dwelling units.

School Impact Fees ($5,000–$15,000)

• Fund school construction and capacity in your district
• Varies by school district — some districts have significantly higher fees than others
• ADUs may qualify for reduced rates compared to full single-family homes

Transportation Impact Fees ($3,000–$8,000)

• Fund road improvements and transportation infrastructure
• Calculated based on expected trip generation from the new dwelling
• ADUs typically generate fewer trips than standard homes, resulting in lower fees

Park Impact Fees ($2,000–$5,000)

• Fund park acquisition and development
• Based on dwelling type and expected population
• Not assessed in all areas of King County

Fire District Impact Fees ($1,000–$3,000)

• Fund fire station and equipment needs
• Varies by fire district
• Not assessed in all districts

Utility Connection Fees: $8,000–$16,000

Connecting your DADU to utilities involves both one-time connection fees and ongoing service charges.

Sewer Connection ($5,000–$10,000)

• Capacity charge to the sewer district
• Connection permit fee
• Inspection fee
• Varies significantly by sewer district — some King County districts charge considerably more than others

Water Connection ($2,000–$6,000)

• New water meter installation (if required)
• Backflow prevention device
• Connection and inspection fees
• Some utilities allow shared meters; others require separate metering

Electrical Service ($1,000–$3,000)

• If a new service panel is required, Puget Sound Energy charges for the new connection
• If tapping off the existing home’s panel with a subpanel, utility fees are minimal

Plan Review Fees: $5,000–$10,000

Plan review fees cover the cost of having county staff review your architectural and engineering drawings.

• Building plan review: Typically 65–80% of the building permit fee
• Fire review: $500–$1,500
• Health review: $500–$2,000 (primarily for septic properties)
• Stormwater review: $500–$1,500

Some jurisdictions bundle plan review into the building permit fee; others charge separately. Confirm with your jurisdiction.

Other Permit-Related Fees

Several smaller fees round out the total permit cost:

• Technology/surcharge fee: $200–$500. Funds the online permitting system.
• State building code surcharge: $25–$100. Required by Washington State on all building permits.
• Address assignment: $100–$300. Your DADU needs its own address for utilities and emergency services.
• Notice on title recording: $100–$200. See our notice on title guide.
• Demolition permit (if applicable): $500–$2,000. If an existing structure must be removed.
• Grading permit (if applicable): $1,000–$3,000. Required for significant site grading.

Fee Reduction Programs

Some fee reductions may be available for DADU projects:

• ADU fee waivers: Some jurisdictions waive or reduce impact fees for ADUs, particularly those committed to affordable housing
• Senior or low-income occupancy: Units designated for seniors or low-income tenants may qualify for fee reductions
• First ADU incentives: A few jurisdictions offer reduced fees for a property’s first ADU

Check with your local jurisdiction for current fee reduction programs. HB 1337 prohibits excessive impact fees for ADUs, so watch for ongoing legislative changes.

Fee Comparison: King County vs. Nearby Cities

• Unincorporated King County: $43,000–$81,000 total
• Seattle: $40,000–$75,000 (streamlined ADU program, but high impact fees)
• Bellevue: $45,000–$85,000 (higher building permit fees)
• Kirkland: $38,000–$70,000 (moderate fees, smaller volume)
• Redmond: $42,000–$78,000 (similar to Bellevue)

These ranges are approximate and change annually. Always verify current fees with the specific jurisdiction.

When Fees Are Due

Understanding when fees are due helps with cash flow planning:

• Application fees: Due at permit submission
• Plan review fees: Due at submission or intake acceptance
• Impact fees: Due at permit issuance (before construction starts)
• Utility connection fees: Due before utility connections are made (during construction)

Total pre-construction cash outlay for fees alone can be $30,000–$60,000. Make sure your financing plan accounts for this timing.

APEX DADU Includes All Fees in Our Estimates

We provide clients with detailed fee breakdowns specific to their jurisdiction and project. When APEX DADU quotes a total project cost, every permit fee, impact fee, and utility connection charge is included — no surprises at the permit counter.

Get a complete DADU fee estimate for your property from APEX DADU