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Zoning Guide

ADU Rules in Boise, Idaho

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ADU Rules in Boise, Idaho

Boise is Idaho's capital and largest city, one of the fastest-growing metros in the United States. The city has a severe housing shortage and has been expanding ADU permissions as part of broader housing policy reforms. Idaho has no statewide ADU preemption law — Boise's local zoning code governs.

Permitted ADU Types

  • Detached ADU: Standalone structure in rear yard
  • Attached ADU: Addition with own entrance and kitchen
  • Garage Conversion: Converting existing garage
  • Interior Conversion: Converting existing space (basement, upper floor)

Size Limits

ADU Type Maximum Size
Detached ADU 700–1,000 sq ft (varies by zone)
Attached ADU 50% of primary dwelling floor area
Garage Conversion Existing footprint

Setbacks

Per Boise Zoning Code (varies by zone):

  • Front: Per base zone (ADUs typically in rear yard)
  • Side: 3–5 feet minimum
  • Rear: 3–5 feet minimum

Height

  • Detached ADU: Maximum 24 feet (2 stories)
  • Cannot exceed height of primary dwelling

Owner Occupancy

Boise may require owner occupancy. Verify current requirements with Planning and Development Services.

Floodplain

Parts of Boise along the Boise River are in FEMA flood zones. Verify flood zone status before planning.

Permit Process

  1. Check zoning: Verify zone via Boise's online zoning map
  2. Floodplain check: If near Boise River
  3. Submit plans: Boise Planning and Development Services
  4. Building permit: City of Boise Building Division
  5. Inspections and CO: Required before occupancy

Contact

City of Boise Planning and Development Services 150 North Capitol Boulevard, Boise, ID 83702 Phone: (208) 384-3830 Website: cityofboise.org/departments/planning-and-development-services

Disclaimer: Boise's ADU regulations have been evolving. Verify current requirements before starting any project.

More about Boise City Zoning

Sources

  1. City of Boise Zoning Code·library.municode.com·Accessed 2026-04-07·Direct link
  2. City of Boise Planning and Development Services·cityofboise.org·Accessed 2026-04-07·Direct link

FAQ

Are ADUs allowed in Boise, Idaho?
Yes. Boise has been actively expanding ADU permissions to address its severe housing shortage. The city allows accessory dwelling units in most residential zones. Idaho has no statewide ADU preemption law.
Why has Boise focused on ADUs?
Boise has been one of the fastest-growing cities in the US and faces a significant housing affordability crisis. The city has expanded ADU allowances as part of broader housing policy to increase housing supply.