Denis Serden
Getting an ADU permit in Clark County is the step most homeowners underestimate. The design decisions, the contractor selection, the financing — those come later. The permit process determines your timeline, your budget buffer, and whether your project moves forward at all.
What Is an ADU? Types That Require Different Permits
An accessory dwelling unit is a secondary living space on a single-family property. The type you build determines which permits are required, how complex the review process is, and how long Clark County or the City of Vancouver will take to approve your plans. There are three main types:
Detached ADU (DADU)
A separate backyard structure. Most flexible for privacy and rental potential. Typical size: 400–1,000 sq ft.
Attached ADU
Connected to the primary home — a garage conversion, added suite, or home addition. Lower cost since you share walls and roof.
Junior ADU (JADU)
Created within the existing home footprint. Maximum 500 sq ft under state law.
Washington State ADU Law in 2025: What Senate Bill 5258 Means for Your Permit
Senate Bill 5258 now requires most Washington cities to allow ADUs by-right in all single-family zones. For homeowners pursuing an accessory dwelling unit permit in Washington State, this is the most important legislative change in decades — it eliminates discretionary review in most cases, meaning your permit application goes straight to technical review rather than a public hearing.
- Up to 2 ADUs are allowed per lot in most jurisdictions
- Owner-occupancy requirements have been largely eliminated statewide
- Maximum size: typically 1,000 sq ft or 50% of primary home floor area
- Setbacks: 4–5 feet from rear/side property lines in most Clark County zones
- ADUs cannot be sold separately from the primary home unless subdivided under RCW 58.17
City-specific note: Vancouver, Camas, Ridgefield, and Battleground each have their own ADU ordinances. Always verify with the local planning department before finalizing your design.
What Does It Cost to Build an ADU in Washington? (Including Permit Fees)
- Garage conversion: $45,000–$80,000
- Attached addition ADU: $90,000–$160,000
- Detached ADU (400–800 sq ft): $140,000–$250,000
- Permit fees (Clark County): $3,500–$8,000
- Utility connections: $5,000–$20,000
A 1-bedroom ADU in the Vancouver metro renting at $1,400–$1,800/month generates $16,800–$21,600 per year in gross rental income. A $180,000 detached ADU reaches simple payback in roughly 8–11 years — and adds property value from day one.
Permits, Inspections & Timeline
A typical detached ADU in Clark County requires a building permit, plus separate electrical, mechanical, and plumbing permits. Current processing time: 4–8 weeks. Total timeline from permit submission to move-in: 5–9 months. Garage conversions typically run 2–4 months.
Financing Your ADU in Washington State
- Cash-out refinance or HELOC: Most common for homeowners with equity.
- Construction loan: Short-term financing that converts to a permanent mortgage at completion.
- Washington State Housing Finance Commission: Piloted below-market ADU financing for qualifying homeowners — check their website for 2025 availability.
- Fannie Mae HomeStyle or FHA 203(k): Renovation loans that allow ADU construction to be rolled into a mortgage.
How a General Contractor Manages the ADU Permit Process for You
The ADU permit process in Clark County involves coordination across multiple agencies, multiple trade permits, and a sequence of inspections that must happen in the right order. A licensed general contractor does not just build the structure — they manage the entire permit workflow on your behalf.
Serden Group has managed ADU permit applications and construction across Clark County — including detached cottages, garage conversions, and attached in-law suites in Vancouver, Camas, Ridgefield, and Battleground.
Ready to start the ADU permit process in Clark County or Vancouver, WA? Start with a site assessment. Schedule your free consultation.