ADU Rules in Ketchikan, Alaska

Ketchikan is Alaska's southernmost city, known as the "Salmon Capital of the World." It receives the highest rainfall of any Alaskan city (150+ inches/year) and has extremely steep terrain. These factors significantly constrain available building sites. The Ketchikan Gateway Borough permits ADUs in residential zones.

Permitted ADU Types

• Detached ADU: A separate structure where terrain permits
• Attached ADU: An addition to the primary home with its own entrance
• Conversion ADU: Converting an existing structure to a dwelling unit

Size Limits

Setbacks

• Front: Must comply with base zone standard
• Side: 5 feet minimum
• Rear: 15 feet minimum

Height

• Detached ADU: Maximum 25 feet
• Cannot exceed height of primary structure

Terrain and Drainage

Ketchikan's steep topography creates significant construction challenges:

• Many lots require retaining walls and engineered foundations
• Steep slopes (over 25%) require geotechnical analysis
• Hillside development may require landslide hazard assessment
• Stormwater management is critical given extreme rainfall

Moisture and Construction

• Annual precipitation exceeds 150 inches — waterproofing is essential
• Moisture-resistant building materials required throughout
• Proper ventilation critical to prevent moisture damage and mold

Parking

One off-street parking space required per ADU where physically feasible given terrain.

Permit Process

1. Site assessment: Evaluate terrain, slope, and drainage
2. Zoning check: Confirm eligibility with Borough Planning
3. Geotechnical review: Often required for hillside lots
4. Submit plans: Including drainage and erosion control plans
5. Building permit: Issued by Building Department
6. Inspections: All required phases
7. Certificate of Occupancy: Required before occupancy

Contact

Ketchikan Gateway Borough Planning Department 344 Front Street, Ketchikan, AK 99901 Phone: (907) 228-6615 Website: borough.ketchikan.ak.us/planning

Disclaimer: Ketchikan's terrain and rainfall present unique construction challenges. Verify current requirements with the Borough Planning Department before starting any project.