Boise

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.

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.

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.

• IHFA Home Loans
• IHFA Heroes Loan Program
• IHFA HOME Program
• Idaho Homeowner Assistance Fund

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.

• HB 166 (2023) preemption framework
• Idaho Smart Growth Zoning Module 3 - Accessory Dwelling Units