ADU Construction Permits in Ada County, Idaho

Building an Accessory Dwelling Unit requires complex zoning, structural, and utility permits.

As one of the more densely populated areas in Idaho, Ada County (around 518,935 residents) tends to see higher application volumes at its building department, so it helps to prepare your documentation in advance.

Code Compliance & Inspections

Because of severe winter weather in Idaho, any exterior structures or footings must be set below the local frost line to prevent shifting, as mandated by the Idaho State Building Code.

Zoning & Cost Factors

Idaho generally favors property rights with relaxed state-level oversight, meaning agricultural zoning often dominates outside of major hubs like Boise. Fortunately, Idaho maintains relatively builder-friendly regulations, keeping base permit fees competitive.

In Ada County, you can begin your application online through the county's permit portal, or submit blueprints and a property survey in person. Including your contractor's Idaho Division of Occupational and Professional Licenses license number helps avoid rejections.

Typical Submittal Package

When applying for a ADU Construction permit, you or your contractor will generally need to submit the following documentation for the city's review:

Standard Ordinances & Processing Time

Key code points for a ADU Construction in Ada County: ADUs typically have maximum square footage limits (often 800-1200 sq ft), height restrictions, and usually require dedicated off-street parking depending on local zoning.

Typical processing time: a few days to several weeks, depending on current workload and the season. Contact Ada County Development Services for a current estimate.