ADU Zoning Rules in Boise, Meridian, Eagle, and Nampa: What Homeowners Need to Know

Before drawing a floor plan or requesting a quote, the first step for any ADU project is confirming what your specific parcel actually allows. ADU ordinances in Idaho are city-specific and zone-specific—meaning a property two blocks away might have completely different rules than yours.

Skipping this step is the most common mistake homeowners make when exploring ADUs. Committing to a design before confirming zoning feasibility can result in wasted planning costs and significant delays. TH Builds always starts with a zoning research call before any design or estimate work begins.

Boise was one of Idaho's first cities to actively encourage ADU development. Key points under Boise's current code:

• ADUs are permitted in most residential zones (R-1A, R-1B, R-1C, R-1D, R-2, R-3)
• Maximum size: typically 50% of primary residence floor area, up to 700 sq ft for attached; up to 900 sq ft for detached
• Setbacks: generally 3 feet from rear and side property lines for detached ADUs
• No owner-occupancy requirement as of recent code updates
• One ADU permitted per single-family lot
• Separate utility meters allowed and sometimes required

Boise has actively streamlined its ADU permitting process, making it one of the more accessible cities in the region.

Meridian allows ADUs in its residential zones with these general parameters:

• Permitted in R-2, R-4, R-8, and R-15 zones (verify your specific zone)
• Maximum ADU size typically capped at 50% of the primary dwelling or 700 sq ft, whichever is less
• Setbacks vary by zone—typically 5–10 feet from property lines for detached structures
• Off-street parking: at least one additional parking space is generally required
• Design standards require the ADU to be architecturally compatible with the primary structure

Meridian's development code has continued to evolve; confirming current rules for your specific address is essential before planning.

Eagle has historically had more restrictive ADU policies than Boise or Meridian, though recent code updates have made ADUs more accessible:

• ADUs are permitted in R-E, R-1, R-2, and some R-3 zones
• Detached ADUs generally limited to 800 sq ft
• Setback requirements tend to be more conservative—verify specific requirements for your parcel
• Owner-occupancy may be required depending on the zone and ADU type
• Architectural compatibility with the primary structure is required

Because Eagle's rules are more nuanced, a pre-application meeting with the city is often worthwhile before finalizing your project scope.

Nampa has updated its code to allow ADUs more broadly:

• Permitted in most low- and medium-density residential zones
• Maximum size: 800 sq ft for detached ADUs in most zones
• Setback requirements consistent with accessory structure rules for each zone
• One additional off-street parking space typically required
• ADU must be served by the same utility services as the primary dwelling or have a separate meter

Nampa's lower land costs relative to Boise and Meridian make it attractive for investors building ADUs to rent.

ADU ordinances across Idaho have been actively evolving as cities respond to housing demand. Rules that were accurate 12 months ago may have changed. Size limits, setback requirements, parking mandates, and owner-occupancy rules have all been modified in various cities in recent years.

TH Builds stays current on ADU code changes across the Treasure Valley and verifies your specific parcel's rules before any design or planning begins. If you're not sure what your property allows, that's exactly where we start.