Detached ADU (DADU) Permits in City of Issaquah
A standalone backyard cottage with its own foundation, roof, and exterior. Maximum flexibility on layout; highest construction cost. State law bars a city maximum below 1,000 sq ft of gross floor area, except on lots with critical areas (RCW 36.70A.681).
Drops the placement canvas on your parcel for detached adu (dadu) scope. Live setback + coverage + easement checks; packet generation when you’re ready.
Permit fees in City of Issaquah
Fee schedule not yet aggregated — check the City of Issaquah fee schedule directly.
City of Issaquah fee scheduleBuilding permit fee is valuation-based (Issaquah adopts UBC Table 1-A bracket schedule). Plan review fee 65% of building fee. WA state BCC surcharge $6.50/unit. Application fees invoiced via https://mybuildingpermit.com; 3% credit-card service fee or pay by check / exact cash. Impact fees apply on top of permit fee: traffic concurrency, school, parks. HB 1337 caps ADU impact fees at 50% of single-family unit rate — confirm Issaquah's current adopted ADU schedule at fee schedule URL. King County sewer capacity charge (~$8k-$10k) applies separately if ADU is on the King County sewer system.
Review timeline
Typical: 45–120 business days
What a DADU permit packet contains
- A1.1 — Site plan with rotated footprint, setbacks, coverage
- A2.1 — Floor plan with rooms, openings, egress
- A3.1 — Elevations (all four faces, dim strings)
- A4.1 / A4.2 — Foundation + framing plans
- A5.1 — Wall section with WSEC R-values
- A6.0 — Glazing schedule (NFRC U-factor + SHGC)
- Filled application forms (city-specific)
- Manual J energy compliance report