Idaho

Idaho's rapid population growth has put pressure on housing markets across the state, and accessory dwelling units offer a way for homeowners to add supply on existing lots. Boise and other cities have adopted ADU ordinances to meet demand. ADU Pass helps Idaho property owners handle the permit paperwork.

319 ZIP codes
46 Counties
228 Cities

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State ADU details

State ADU law

Idaho enacted statewide ADU preemption through HB 166 (2023), passed by the Sixty-seventh Idaho Legislature and signed by Governor Brad Little, effective 2023-07-01. The act guarantees at least one ADU per residentially-zoned, owner-occupied lot in covered jurisdictions and prohibits cities and counties from outright banning ADUs in residential zones. Local governments may still impose health, safety, and infrastructure standards (parking, setbacks, design review) but may not impose hard maximum size caps. The act simultaneously preempts HOA / restrictive-covenant bans on ADUs as of the effective date (see stateHoaPreemption); covenants recorded before 2023-07-01 are NOT grandfathered for blanket prohibitions on owner-occupied homesteads, distinguishing Idaho from Hawaii's grandfathering approach. The legislature created a follow-on study committee on state and local land-use regulations whose recommendations have produced additional measures in subsequent sessions.

checked 2026-04-26

State HOA preemption

Idaho HB 166 (2023) preempts HOA and restrictive-covenant bans on ADUs as of 2023-07-01. HOAs cannot create or enforce rules that generally ban ADUs on detached, owner-occupied properties. As of 2023-07-01, no new restrictive covenants may be created to prohibit ADUs on owner-occupied homesteads. HOAs retain authority to impose 'reasonable regulations' on ADUs (size, parking, design, materials) within the bounds of the state floor; they may not use those reasonable regulations to effectively ban ADUs. Idaho's preemption is broader than Hawaii's (which grandfathers pre-Act covenants) but narrower than Colorado's (which voids ALL HOA ADU prohibitions): Idaho focuses specifically on owner-occupied homesteads. The Idaho Homeowner's Association Act, Idaho Code Title 55 Chapter 32, governs HOA powers generally.

checked 2026-04-26

State financing programs

Idaho does not operate an ADU-specific statewide loan, grant, or forgivable-loan program. The Idaho Housing and Finance Association (IHFA) is the state's housing finance agency and administers a robust portfolio: first-time-homebuyer mortgages, down-payment assistance, the IHFA Heroes Loan Program (for first responders, military, healthcare, educators), the federal HOME Investment Partnerships Program (gap financing for affordable rental development), and the federal Low-Income Housing Tax Credit allocation. None target ADU construction directly; an ADU-bearing primary residence on an Idaho lot can qualify for the underlying mortgage when other criteria are met. The Idaho Homeowner Assistance Fund operates as a federally-funded mortgage and utility backstop.

checked 2026-04-26

State insurance regimes

Idaho does not operate a state FAIR plan, wind pool, or wildfire-specific residual market. Idaho is one of approximately 17 US states without a FAIR Plan, leaving owners denied coverage in the admitted market to use the surplus-lines market. The Idaho Department of Insurance (DOI, https://doi.idaho.gov/) regulates standard homeowners and dwelling-fire products under Idaho Code Title 41. Wildfire risk in Idaho's wildland-urban interface (particularly Boise foothills, McCall, Idaho City, and Sun Valley areas) is the principal ADU-relevant exposure: as of 2025-2026, approximately 22-25 insurers have non-renewed some or all Idaho policies driven by wildfire concerns. Statewide average homeowners premium rose from $1,308 (2022) to $1,798 (2024). The DOI issued a property-insurance-market data call in 2025 to assess capacity and is studying FAIR Plan options, but no FAIR Plan has been authorized as of 2026-04-26.

checked 2026-04-26

State housing programs

Idaho's state-level ADU programs operate primarily through the HB 166 preemption framework (effective 2023-07-01) rather than a separate pre-approved-plan catalog or fee-waiver statute. The state does not maintain a statewide ADU plan library. Idaho Smart Growth (a nonprofit) maintains widely-used model ADU zoning module guidance. The Idaho Legislature's land-use study committee, formed after HB 166, has issued recommendations that have produced incremental land-use legislation but no statewide ADU plan or fee-waiver program. ADU-relevant programs at the state level are essentially limited to the HB 166 preemption itself.

checked 2026-04-26

Known state issues (2)

  • policy-review (since 2023-07) — Practitioners working in Idaho should verify each city's current ADU ordinance; the HB 166 floor applies as a backstop where local codes have not been updated. (source)
  • policy-review (since 2025) — ADU owners in wildland-urban interface zones (Boise foothills, McCall, Sun Valley, Idaho City) should plan for surplus-lines as the only fallback if admitted-market coverage is unavailable. Cost of insurance is a material ADU operating expense in WUI zones. (source)
Federal (United States) — ADU-relevant rules and programs

Federal ADU law

The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.

checked 2026-04-20

Federal financing programs

Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.

checked 2026-04-20

Federal tax credits

There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.

checked 2026-04-20

Federal housing programs

HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.

checked 2026-04-20

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