Accessory Structures in Ada County, ID (2026)
6 county-level rules, plus city-specific rules for 1 city in Ada County, Idaho.
Verified from official government sources
ADU Rules
Unincorporated Ada County allows one secondary (accessory) dwelling per lot of at least 6,000 square feet. It must be 350 to 1,200 square feet, or 60% of the principal home's above-ground living space, whichever is less, and capped at three bedrooms.
Accessory Dwelling Unit (Secondary Dwelling) Rules in Ada County
Some RestrictionsAda County Code 8-4-23(C)(1)
A secondary dwelling may be between three hundred fifty (350) square feet up to a maximum of one thousand two hundred (1,200) square feet or sixty percent (60%) of the square footage of above-ground living space of the principal dwelling, whichever is less. a. Sixty Percent (60%) Calculation: The square footage of covered outdoor space, basements or attached/detached garages associat...
ADU Owner Occupancy
Ada County Code 8-4-23(B)(3) requires that either the principal home or the secondary dwelling stay continuously occupied by at least one person with an ownership interest in the property. The rule applies to every secondary attached or detached dwelling approved under Section 8-4-23, on top of a 6,000-square-foot minimum lot size and a one-ADU-per-property cap.
ADU Owner-Occupancy Rule in Ada County
Significant RestrictionsAda County Code § 8-4-23(B)(2)-(4)
3. Occupancy: Either the principal dwelling or the secondary dwelling must be continuously occupied by at least one (1) person having ownership interest in the subject property. 4. Property Size: The subject property shall have a minimum property size of at least six thousand (6,000) square feet. 5. Dimensional Standards: All secondary dwellings shall meet the dimensional standards for the appl...
ADU Rental Restrictions
Ada County Code 8-4-23(F) requires a recorded deed restriction on every secondary dwelling stating that once no owner remains living in either the main house or the ADU, the secondary dwelling automatically becomes non-habitable space and shall not be rented or leased for any purpose. The restriction binds all future owners as long as the ADU exists.
ADU Rental Ban When Owner-Occupancy Ends
Heavy RestrictionsAda County Code § 8-4-23(F)(1)
F. Deed Restriction: A recorded deed restriction is required ensuring compliance with the following requirements and shall be submitted prior to issuance of a certificate of occupancy or final building permit inspection. 1. Document Requirements: The deed restriction or covenant shall address the following topics: a. The secondary dwelling shall not be sold or owned separately from the principa...
Shed & Carport Rules
In unincorporated Ada County, a detached accessory structure (shed, garage, workshop) may not exceed 24 feet in height, cannot sit in a required setback or on an easement, and cannot be used as a dwelling. Small sheds 200 sq ft or less may sit in side or rear required yards.
Shed and Accessory Structure Rules in Unincorporated Ada County
Some RestrictionsAda County Code 8-4-2(B)(3)
Height Standards. An accessory structure shall not exceed a height of twenty-four feet (24').
Garage Conversions
Unincorporated Ada County lets you convert an existing garage, basement, or detached accessory structure into a secondary dwelling, provided it meets the Section 8-4-23 standards, the Ada County Building Code, plumbing and electrical codes, and off-street parking for both units.
Garage and Accessory Structure Conversions in Ada County
Some RestrictionsAda County Code 8-4-23(E)
An existing garage, basement or a detached accessory structure may be converted into a secondary dwelling, provided that the conversion or structure meets the standards of this Section, along with all applicable requirements of the Ada County Building Code.
Tiny Homes
Ada County's zoning code treats a tiny home as a manufactured home. A tiny home used as a second unit must meet the secondary-dwelling standards of Section 8-4-23 (350 to 1,200 sq ft, foundation, deed restriction). A tiny home on wheels is a recreational vehicle, not a permanent dwelling.
Tiny Home Rules in Unincorporated Ada County
Some RestrictionsAda County Code Title 8, Ch. 10 (Manufactured Home)
Manufactured Home: A structure, transportable in one or more sections, built on a permanent chassis and designed for use as a dwelling... This includes Tiny Homes and Park Models. The term 'manufactured home' does not include a 'recreational vehicle.'
Accessory Structures by City in Ada County
1 cities in Ada County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
All Ada County ordinances
See every category we cover for Ada County: parking, noise, fences, fires, animals, pools, and more.
Ada County Ordinance Hub →