ADU rules in Boise, ID — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Boise allows one ADU (attached or detached) on every single-family lot. Idaho Code Section 67-6511A (2023) limits cities from banning ADUs in single-family zones. Boise permits ADUs up to 900 sq ft with streamlined review.
Idaho Code Section 67-6511A requires cities to allow at least one ADU per single-family lot and prohibits owner-occupancy mandates that would make ADUs impractical. Boise Development Code Chapter 11-04-03.3 implements this with permitted ADUs up to 900 sq ft or 10% of lot area, detached or attached. Maximum height typically matches the principal dwelling. Setbacks are 4 ft side/rear for detached ADUs under 15 ft tall. One additional parking space is encouraged but not required in transit-served areas. Short-term rental of ADUs is allowed if registered with the city. ADUs in Historic Districts require HPC review. No separate utility meters are required; ADUs may share the principal unit services.
Contact your local code enforcement office for specific penalty information.
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See how Boise's adu rules rules stack up against other locations.
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