In plain words

Idaho passed a statewide ADU law in 2026. An accessory dwelling unit, or ADU, is a small second home on the same lot as a house. It can be inside the house, attached to it, or a separate backyard building. The law is Senate Bill 1354, and it took effect July 1, 2026. It covers cities with more than 10,000 people. It does not cover counties or smaller towns. Covered cities may not ban ADUs in residential zones. Zoning is the local rulebook for what can be built where. By February 1, 2027, these cities must update their rules. They must allow one ADU per single-family lot, either inside the house or detached. They cannot require the owner to live on the property, a rule called owner occupancy. They cannot cap an ADU below 1,000 square feet or 75% of the main home's size. They cannot charge higher impact or hookup fees than for other homes. They can require parking only in some cases, such as homes within a quarter mile of transit, jobs or shops. An ADU that meets the city's written standards must be approved by staff, by right. By right means no public hearing or vote is needed. Historic districts are left out. Building codes, fire rules, and water and sewer limits still apply. A separate state law limits homeowners associations, or HOAs. An HOA generally cannot create or enforce rules that ban or limit ADUs. HOAs can still set reasonable rules on design, size, height, setbacks and parking. You may be able to build an ADU if local rules and your property allow it.

The rules at a glance

State ADU lawYes
Where the state rule appliesCities with more than 10,000 residents (Idaho Code §67-6541(6)), outside historic districts and designated historic properties. Counties and smaller cities are not covered by the zoning rules. The HOA rule in §55-3212 has no population limit and applies to homeowners associations statewide, and §55-618 voids, statewide, any restrictive covenant signed on or after July 1, 2023 that bans an internal ADU.
Approved without a hearing?Yes. Qualifying ADUs are approved by staff review, without a discretionary hearing.
Kinds of ADU the state protectsinternal, attached, detached
ADUs per lot1 ADU per single-family lot (either one internal ADU or one detached ADU)
Owner living on siteTowns can’t require the owner to live on the property.
ParkingCovered cities may not require off-street or guest parking for an ADU unless the main home has no off-street parking, the street is unpaved or not built for on-street parking, or the main home is within a quarter mile of transit, an employment area or commercial services.
SizeCovered cities may not cap an ADU below 1,000 sq ft or 75% of the main home's size, and may not set a height limit lower than the existing main home. The statute does not say which of the two size figures controls when they differ.
Lot size and setbacksCovered cities may not make ADU rules on setbacks, lot size, lot coverage or frontage stricter than the rules for single-family homes in the same zone. A detached ADU may go in the rear yard or must follow the main home's setbacks (a setback is the required gap between a building and a property line). Setbacks for rights-of-way and easements still apply.
FeesCovered cities may not charge impact fees or utility connection fees on an ADU that are higher than those charged to other single-family homes.
Short-term rentalsIdaho Code §67-6539 bars cities and counties from banning short-term rentals or adding special permits, fees or owner-occupancy rules for them, so local governments cannot single out ADUs used as short-term rentals. Homeowners associations are a different matter: the HOA protection in §55-3212 does not apply to short-term rentals as defined in §63-1803(4).
Can towns opt out?No

What to do next

  1. Check whether your property is inside a city of more than 10,000 people. If it is in unincorporated county land or a smaller town, that county or town's own rules apply instead.
  2. Ask your city planning office whether it has updated its code for Idaho Code §67-6541 (deadline February 1, 2027) and how it is handling ADU applications in the meantime.
  3. Find out whether your lot is in a historic district or is a designated historic property, since the state ADU rules do not apply there.
  4. Read your HOA covenants. Under Idaho Code §55-3212 an HOA generally cannot ban or limit ADUs, but it can set reasonable rules on design, size, height, setbacks, open space, parking and bedrooms.
  5. Confirm water, sewer or septic capacity and building-code needs early, and ask whether free pre-approved plans exist where you live, as they do in Boise and through a housing partnership in Coeur d'Alene.

What your town still decides

Idaho's zoning power sits with cities and counties under the Local Land Use Planning Act (Idaho Code Title 67, Chapter 65). The 2026 ADU law narrows that power only for cities of more than 10,000 people. Those cities had to stop banning ADUs in residential zones when the law took effect on July 1, 2026, and must adopt plan and code changes through the normal notice-and-hearing process by February 1, 2027. Until a city finishes, its old code may still be on the books, so ask how it is applying the new state rules. Cities may always be more generous than the state floor. Building codes, fire and floodplain rules, water, sewer, road and utility capacity, aquifer, slope and habitat protections still apply. Counties and towns of 10,000 or fewer keep full control and write their own ADU rules, if any. Idaho also bars local bans on short-term rentals. Lawmakers adopted SCR 103 in 2025 to create a housing study committee, and in 2026 they passed the ADU law alongside a separate starter-home subdivision law (S1352, Idaho Code §67-6542).

Examples of local rules

  • Boise: Boise's zoning code (Section 11-03-03.2B) allows ADUs in the R-1A, R-1B, R-1C, R-2, R-3, MX-1, MX-2, MX-3, MX-U, A-1 and A-2 zones. Minimum lot area and density limits do not apply. One ADU per lot is allowed, capped at 900 sq ft or 70% of the main home (whichever is smaller) and two bedrooms. ADUs go through staff-level planning review, then a building permit. That size cap is below the new state floor of 1,000 sq ft or 75%, so expect Boise to revise it by February 2027. In March 2026 the city released eight free pre-approved ADU plans, 280 to 695 sq ft. Source
  • Coeur d'Alene: Coeur d'Alene has allowed ADUs since 2007 and loosened its rules in 2019 and 2021. The city lists them as allowed in the R-8, R-12 and R-17 residential zones, the Downtown Core and overlay districts, the C-17 and C-17L commercial zones, and planned unit developments. The Housing Solutions Partnership offers four free ADU plan sets that local building and planning staff have reviewed. Detailed size and parking rules are in the city code, not on this page. Source

What we’re still confirming

  • The law requires cities to allow one inside or one detached ADU per lot, but it's unclear whether the owner or the city picks which type.
  • Cities can't cap ADUs below 1,000 sq ft or 75% of the main home, but the law doesn't say which number controls when the main home is small.

Laws, bills and citations

The laws behind this (3)
  • Accessory dwelling units (S1354) (Idaho Code §67-6541 and §55-3212, as enacted and amended by S1354 (2026), 2026 Idaho Sess. Laws ch. 265, signed March 31, 2026, in effect July 1, 2026). Bars cities of more than 10,000 people from banning ADUs in residential zones, and requires them to rewrite their plans and codes by February 1, 2027 to allow one internal or one detached ADU per single-family lot, with no owner-occupancy rule, a size cap no lower than 1,000 sq ft or 75% of the main home, no impact or hookup fees higher than other single-family homes pay, limited parking demands, clear and objective standards, and staff-level approval as a matter of right. It also rewrites §55-3212 so homeowners associations generally cannot add or enforce covenants that ban or limit ADUs unless the owner agrees in writing. Read it
  • Short-term rental limits on cities and counties (H583) (Idaho Code §67-6539, as amended by H583 (2026), 2026 Idaho Sess. Laws ch. 22, signed March 16, 2026, in effect July 1, 2026). Not an ADU law, but it controls how any home, including an ADU, can be rented short term. Cities and counties may not ban short-term rentals or treat them differently from other homes, may not require owner occupancy, permits, licenses, fees or registration, and may impose only a short list of safety rules such as smoke alarms and fire extinguishers. Read it
  • Covenant limits on internal ADUs (H166) (Idaho Code §55-3212 (as originally added) and §55-618, both added by H166 (2023), 2023 Idaho Sess. Laws ch. 265, signed April 3, 2023, in effect April 3, 2023). First statewide ADU protection in Idaho. Section 55-3212 stopped homeowners associations and others from adding, amending or enforcing covenants that flatly banned one internal ADU inside an owner-occupied homestead (or its garage) used for relatives or for rentals longer than 30 days; the 2026 law replaced that rule with a broader one. Section 55-618, still in force, voids any restrictive covenant signed on or after July 1, 2023 that bans an internal ADU, and makes anyone who tries to create or enforce one liable for the other side's legal fees and damages. Covenants signed before July 1, 2023 are not affected by 55-618. Read it
Proposed and failed bills (1). None of these is law.
  • S1277 (2026): died as of October 3, 2026. An earlier 2026 ADU bill on the same subject as S1354, covering HOA covenants and local zoning. It was introduced February 11, 2026 and sent to the Senate Commerce and Human Resources Committee, where it got no further action. S1354, introduced in March, became law. Bill page

Sources

  1. Idaho Code §67-6541 and §55-3212, as enacted and amended by S1354 (2026), 2026 Idaho Sess. Laws ch. 265 · official source
  2. Idaho Code §67-6539, as amended by H583 (2026), 2026 Idaho Sess. Laws ch. 22 · official source
  3. Idaho Code §55-3212 (as originally added) and §55-618, both added by H166 (2023), 2023 Idaho Sess. Laws ch. 265 · official source
  4. Idaho Code §67-6541, Accessory Dwelling Units (Idaho Legislature) · official source · checked 2026-10-03
  5. Idaho Code §55-3212, Prohibited conduct, restrictions on accessory dwelling units (Idaho Legislature) · official source · checked 2026-10-03
  6. Idaho Code §67-6539, Limitations on regulation of short-term rentals (Idaho Legislature) · official source · checked 2026-10-03
  7. Idaho Code §67-6542, Starter home subdivisions (Idaho Legislature) · official source · checked 2026-10-03
  8. Idaho Code Title 67, Chapter 65 index, Local Land Use Planning Act (Idaho Legislature) · official source · checked 2026-10-03
  9. S1354 (2026) bill text as introduced · official source · checked 2026-10-03
  10. H166 (2023) text as amended in the Senate (adds §55-3212 and §55-618) · official source · checked 2026-10-03
  11. Idaho Code §55-618, Internal accessory dwelling units, restrictive covenants prohibited (Idaho Legislature) · official source · checked 2026-10-03
  12. S1277 (2026) bill page · official source · checked 2026-10-03
  13. 2026 Idaho legislation list (status of housing and land-use bills) · official source · checked 2026-10-03
  14. 2025 Idaho legislation list (SCR 103 housing study committee) · official source · checked 2026-10-03
  15. City of Boise: Quick Guide to Accessory Dwelling Units · official source · checked 2026-10-03
  16. City of Boise news: City provides free ADU plans (March 17, 2026) · official source · checked 2026-10-03
  17. City of Coeur d'Alene: Accessory Dwelling Units (ADUs) · official source · checked 2026-10-03

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.