PERCH · ADU LEGALITY INDEX · UPDATED 2026-07-17

ADU Laws in Idaho — 2026 Guide

Statute summary, size caps, owner-occupancy rules, permit timelines, and a 4-question eligibility quiz. Part of the PERCH ADU Legality Index — one page per state, verified against real statute references and updated as laws change.

4-question eligibility quiz

Q1 · State
What state are you building in?
Q2 · Lot size
How big is the lot?
Q3 · Zoning
What zoning district is the lot in?
Q4 · Property type
Which best describes the build?
Result

Key rules · Idaho

Statute summaryIdaho has no statewide ADU preemption. Boise permits ADUs on most residential lots ≥5,000 sqft under Municipal Code Title 11. Coeur d'Alene expanded pathways 2023.
ADU allowedConditional — depends on jurisdiction
Size cap (sqft)900
Owner-occupancy requiredNo
Permit timeline (days)40-100
Statute citationIdaho Code § 67-6511
Last verified2026-07-17

Frequently Asked Questions

Are ADUs legal in Idaho?
Conditionally — ADU legality in Idaho depends on the specific municipality. Consult your local planning department; Idaho has no statewide ADU preemption. Boise permits ADUs on most residential lots ≥5,000 sqft under Municipal Code Title 11. Coeur d'Alene expanded pathways 2023.
What are the size limits on an ADU in Idaho?
Idaho permits ADUs up to approximately 900 square feet per Idaho Code § 67-6511. Individual municipalities may set lower caps; verify with your city or county planning department before ordering.
Do I need a permit for an ADU in Idaho?
Yes — every ADU in Idaho requires a building permit issued by the city or county. The permit process typically runs 40-100 days depending on jurisdiction, complexity, and whether discretionary review is triggered.
Can I rent out my ADU in Idaho?
Long-term rental is generally permitted in Idaho where the ADU itself is legal. Short-term rental (under 30 days) is subject to municipal registration and may require additional permits; check with your local planning department.
Does Idaho require owner-occupancy on the primary residence when I have an ADU?
No — Idaho does not require owner-occupancy under state statute per Idaho Code § 67-6511. Local ordinances may still add owner-occupancy requirements in specific cities.
What zoning districts allow ADUs in Idaho?
Most Idaho municipalities permit ADUs in single-family residential zones (R-1, R-2 equivalent). Idaho has no statewide ADU preemption. Boise permits ADUs on most residential lots ≥5,000 sqft under Municipal Code Title 11. Coeur d'Alene expanded pathways 2023. Consult your city zoning code for the specific district table.
How long does an ADU permit take in Idaho?
Typical ADU permit timelines in Idaho run 40-100 days from application to approval. Fast-permitting counties can move in under 30 days; metro-core jurisdictions with discretionary review can extend to 150+ days.
Are there setback requirements for an ADU in Idaho?
Yes — most Idaho municipalities apply the same setback requirements to ADUs that apply to the primary structure (typically 5-10 feet rear and side, 15-25 feet front). Some cities apply reduced setbacks specifically for detached ADUs. Verify with your city zoning code.
Can I finance an ADU purchase in Idaho?
Yes — several financing pathways cover ADU purchases in Idaho: Fannie Mae HomeStyle Renovation, FHA 203(k), construction-to-perm loans, HELOC on the primary residence, and cash. Check with modular-friendly lenders like 21st Mortgage, Cascade Financial, and Triad Financial for the Idaho-specific product.
What's the difference between an ADU and a JADU in Idaho?
The JADU (Junior ADU) category originated in California and is not a distinct legal category in Idaho. Most Idaho municipalities regulate internal conversions and detached units under a single ADU/accessory apartment definition.

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