A summary of Boise ADU rules under ZOA25-000013 (2026), including maximum size, setbacks, owner-occupancy, parking, and the eight free pre-approved plans.
This guide summarizes Boise accessory dwelling unit rules based on City of Boise Zoning Code amendment ZOA25-000013. Effective date: 2026-02-15. This is not legal advice. Standards change. Verify all information at https://www.cityofboise.org/departments/planning-and-development-services/planning/boise-zoning-code/pre-approved-adu-plans/ before making any development or acquisition decision.
Applicable code
Code references active as of publication. Verify current standards at the official source before any development decision.
Up to two (2) accessory dwelling units are allowed per lot in residential zoning districts.
Investor implication: Investors can now develop two ADUs on a single lot, doubling rental income potential compared to the previous one-ADU limit. This applies to detached, attached, and junior ADU configurations.
Standard ADUs: Maximum 900 square feet or 70% of the primary dwelling's gross floor area, whichever is greater. Junior ADUs: Maximum 500 square feet.
Investor implication: The 70% rule allows larger ADUs on properties with larger primary dwellings, creating flexibility for higher-end rental units. Junior ADUs offer a lower-cost conversion path for existing interior space.
ADUs facing an alley may be placed as close as 3 feet from the rear property line.
Investor implication: Alley-facing lots gain buildable area, making ADU development viable on smaller or constrained parcels. This is particularly valuable in established neighborhoods like The Bench and North End.
No parking is required for ADUs located within one-half mile of a frequent transit corridor.
Investor implication: Transit-proximate properties eliminate parking construction costs, improving ADU project economics. Verify transit corridor maps before acquisition.
Cities may not require owner-occupancy for ADU approval.
Investor implication: Non-owner-occupied investment properties can now add ADUs without triggering occupancy restrictions, expanding the investor pool and rental inventory potential.
Renew analysis
Investors can now develop two ADUs on a single lot, doubling rental income potential compared to the previous one-ADU limit. This applies to detached, attached, and junior ADU configurations.
The 70% rule allows larger ADUs on properties with larger primary dwellings, creating flexibility for higher-end rental units. Junior ADUs offer a lower-cost conversion path for existing interior space.
Alley-facing lots gain buildable area, making ADU development viable on smaller or constrained parcels. This is particularly valuable in established neighborhoods like The Bench and North End.
Transit-proximate properties eliminate parking construction costs, improving ADU project economics. Verify transit corridor maps before acquisition.
Non-owner-occupied investment properties can now add ADUs without triggering occupancy restrictions, expanding the investor pool and rental inventory potential.
Pre-approved plans eliminate architectural design costs and accelerate permitting timelines, reducing soft costs and time-to-market for ADU projects.