Are ADUs allowed in Ketchikan, Alaska?

Yes. Ketchikan and the surrounding Ketchikan Gateway Borough permit accessory dwelling units in residential zones. The city's steep terrain limits developable land, making ADUs valuable for housing.

What is the maximum ADU size in Ketchikan?

Accessory dwelling units in the Ketchikan area are generally limited to 800 square feet or 50% of the primary dwelling's floor area, whichever is less.

Is Ketchikan's extreme rainfall a factor in ADU construction?

Yes. Ketchikan receives over 150 inches of rain annually. ADU construction must incorporate excellent drainage, waterproofing, and moisture-resistant materials.

ADU Rules in Ketchikan, Alaska | Zoning Guide by Building Club

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

ADU Type	Maximum Size
Detached ADU	800 sq ft or 50% of primary dwelling
Attached ADU	50% of primary dwelling floor area
Conversion ADU	Existing footprint

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

Site assessment: Evaluate terrain, slope, and drainage
Zoning check: Confirm eligibility with Borough Planning
Geotechnical review: Often required for hillside lots
Submit plans: Including drainage and erosion control plans
Building permit: Issued by Building Department
Inspections: All required phases
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.

ADU Rules in Ketchikan, Alaska