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 accessory dwelling units are allowed per lot in all residential zoning districts.
Investor implication: Doubles the rental income potential per parcel compared to the previous one-ADU limit. Particularly valuable on larger lots where two detached units can be positioned to maximize privacy and rent premiums.
Verify at City of Boise ZOA25-000013 ADU Amendment →Maximum size for a standard ADU is 900 square feet or 70% of the primary dwelling's gross floor area, whichever is greater.
Investor implication: The 70% provision allows larger ADUs on properties with larger primary homes, increasing rental yield potential on premium lots. On a 2,000 sq ft primary, you can build a 1,400 sq ft ADU.
Verify at City of Boise ZOA25-000013 ADU Amendment →Junior ADUs are allowed up to 500 square feet and must be contained within or attached to the primary dwelling.
Investor implication: Junior ADUs are lower-cost conversions (basement, garage, attic) but cannot be detached. Useful for maximizing unit count without new foundation work.
Verify at City of Boise ZOA25-000013 ADU Amendment →Detached ADUs facing an alley may be placed as close as 3 feet from the rear property line.
Investor implication: Alley-facing lots gain significant buildable area. A 3-foot setback allows larger ADU footprints and better site utilization compared to standard 5-foot rear setbacks.
Verify at City of Boise ZOA25-000013 ADU Amendment →No off-street parking is required for ADUs located within one-half mile of a frequent transit stop.
Investor implication: Eliminates parking as a constraint on transit-adjacent lots. Particularly valuable in North End, East End, and BSU Area where lot sizes are smaller and parking construction is expensive.
Verify at City of Boise ZOA25-000013 ADU Amendment →No owner-occupancy requirement. ADUs may be rented independently of the primary dwelling.
Investor implication: Allows full investor ownership and rental of all units on the lot. No requirement to live on-site. Critical for out-of-state or institutional buyers.
Verify at City of Boise ZOA25-000013 ADU Amendment →Eight pre-approved ADU plans (280–695 sq ft) are available at no cost from the City of Boise.
Investor implication: Eliminates architectural design costs (typically $5,000–$15,000) and reduces permitting timeline. Plans are stamped and ready for submittal.
Verify at City of Boise Pre-Approved ADU Plans →Renew analysis
Doubles the rental income potential per parcel compared to the previous one-ADU limit. Particularly valuable on larger lots where two detached units can be positioned to maximize privacy and rent premiums.
The 70% provision allows larger ADUs on properties with larger primary homes, increasing rental yield potential on premium lots. On a 2,000 sq ft primary, you can build a 1,400 sq ft ADU.
Junior ADUs are lower-cost conversions (basement, garage, attic) but cannot be detached. Useful for maximizing unit count without new foundation work.
Alley-facing lots gain significant buildable area. A 3-foot setback allows larger ADU footprints and better site utilization compared to standard 5-foot rear setbacks.
Eliminates parking as a constraint on transit-adjacent lots. Particularly valuable in North End, East End, and BSU Area where lot sizes are smaller and parking construction is expensive.
Allows full investor ownership and rental of all units on the lot. No requirement to live on-site. Critical for out-of-state or institutional buyers.
Eliminates architectural design costs (typically $5,000–$15,000) and reduces permitting timeline. Plans are stamped and ready for submittal.
This is the highest-yield ADU play in Boise. Alley-facing lots in The Bench and SE Boise are the primary targets. Underwrite assuming 12–18 month construction and lease-up timeline.
Junior ADUs are the lowest-cost path to adding a unit. Best fit for older homes with existing basements in North End, East End, and BSU Area. Rent premiums are lower than detached units, but construction cost is 40–60% less.
Pre-approved plans are the fastest path to permit. Use them unless site constraints (slope, setbacks, existing structures) require custom design. Hill Road and West Boise lots are large enough to accommodate any of the eight plans without setback issues.