ADU rules in Idaho
Representative cities: Boise, Meridian, Nampa.
ADU permit rule
Permit requiredGenerally allowedcity authority
Fee basis
Valuation-based; set by the issuing city or, in unincorporated areas, by Idaho DOPL.
Typical timeline
Plan review typically 1–3 weeks in Treasure Valley cities.
Setback
Per local zoning; ADU setbacks vary by city.
Area threshold
No statewide size exemption; local zoning sets ADU size and lot limits.
Exempt if
None — an ADU always requires a building permit.
Go / no-go
allowed
Idaho has no single statewide ADU mandate; cities adopt ADU rules by local ordinance. Boise and other growing cities allow ADUs subject to zoning. Verify with the local building department.
ADU official sources: Idaho DOPL — Division of Building Safety (state code) · City of Boise — Building Division
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Frequently asked questions
Do I need a permit to build an ADU in Idaho?
Per Idaho rules, an ADU is "yes" for a permit and the authority is "city". Idaho has no single statewide ADU mandate; cities adopt ADU rules by local ordinance. Boise and other growing cities allow ADUs subject to zoning. Verify with the local building department. Always confirm with the issuing building department.
How big can an ADU be in Idaho?
Area threshold: No statewide size exemption; local zoning sets ADU size and lot limits.
What are the ADU setbacks in Idaho?
Setback: Per local zoning; ADU setbacks vary by city.
How much does an ADU permit cost in Idaho?
Fee basis: Valuation-based; set by the issuing city or, in unincorporated areas, by Idaho DOPL.