Idaho's New ADU Law: Where SB 1354 Actually Applies

TL;DR

1. SB 1354 is law. Signed March 31, 2026, effective July 1, 2026, codified at Idaho Code 67-6541. Cities can no longer ban accessory dwelling units in residential zones.
2. It only applies to cities with a population over 10,000. In our area that means Twin Falls, Jerome, and Burley. It does not apply to Kimberly, Buhl, Filer, Rupert, or any smaller town.
3. It does not apply to counties at all. If you're in unincorporated Twin Falls County, this law gives you nothing.
4. Cities have until February 1, 2027 to amend their comprehensive plans and land use regulations. Twin Falls adopted a brand new zoning code on January 1, 2026, three months before this law was signed, so it will have to be revisited.
5. The law requires cities to allow either one internal ADU or one detached ADU per lot. Not both. A lot of coverage online gets this wrong because it describes the original bill rather than the amended version that passed.
6. Owner-occupancy requirements are gone. Cities can no longer require you to live on the property.
7. Qualifying projects must be approved administratively, as a matter of right. No hearing, no discretionary approval.
8. HOA rules changed statewide, not just in big cities, and that change is broader than most people realize.
9. What the law does not touch: building codes, fire safety, septic and water capacity, and easements. In this valley, septic is usually the real constraint.

If you've been thinking about a guest house, a place for a parent, or a rental unit on your lot, the rules changed this summer. Genuinely changed, not adjusted.

But the coverage I've seen has been sloppy, and some of it is flatly wrong, because a lot of it was written about the bill as introduced rather than the version that actually became law. The bill was amended before passage, and the amendments changed the parts that matter most to you.

Here's what the law actually says, where it applies around here, and what it doesn't fix.

What is SB 1354?

Senate Bill 1354 passed the Senate 25 to 10 and the House 47 to 23. Governor Little signed it March 31, 2026. It carried an emergency clause, so it took effect July 1, 2026, and it's now Idaho Code 67-6541.

The core of it is one sentence: no city shall enact or enforce any ordinance, rule, regulation, or policy that bans accessory dwelling units in any residential zoning area within its jurisdiction. An ADU is classified as a residential land use for zoning purposes.

The law defines an accessory dwelling unit as a self-contained living unit that includes its own cooking, sleeping, and sanitation facilities, located on the same lot as a single-family primary dwelling. It can be internal, attached, or detached. It specifically does not include a motorhome, camper, recreational vehicle, tiny home on wheels, or similar dwelling on wheels.

That last exclusion matters. If your plan involves something with wheels, this law does not help you.

Does it apply where I live?

This is where most of the confusion is, and the answer around here is genuinely split.

The statute applies only to cities with a population greater than 10,000. Not counties. Not smaller cities.

Based on the most recent Census figures:

Three cities in our service area are covered. Everywhere else, including our own town of Kimberly, is not.

Worth noting: the bill as originally introduced set the threshold at 5,000, which would have covered Kimberly and Rupert. The Senate amended it to 10,000 before passage. If you read an article saying the threshold is 5,000, that article is describing a version of the bill that never became law.

If you're outside a covered city, you are not out of luck. You're just back to normal rules. Your city or the county can still allow ADUs, and many do under various names. It simply isn't a protected right, and the local jurisdiction sets the terms.

What must covered cities actually do?

By February 1, 2027, each covered city has to amend its comprehensive plan and land use regulations for all land zoned single-family residential. Historic districts and designated historic properties are carved out.

Here's what those amendments have to accomplish:

Allow one ADU per lot, either internal or detached. The statute says cities must allow either one internal accessory dwelling unit within the single-family dwelling or one detached accessory dwelling unit per lot, placed in the rear yard or subject to the setbacks required of the primary dwelling.

Read that carefully, because it's the most commonly misreported provision. The original bill said one internal and one detached. The version that passed says either or. If you've read that Idaho now guarantees you two units, that's the introduced draft, not the law.

No parking mandates, with three exceptions. Cities generally cannot require off-street or guest parking for an ADU. They still can if your principal dwelling has no off-street parking of its own, or if your street is unpaved and not designed for on-street parking, or if your principal dwelling is within a quarter mile of transit, an employment area, or commercial services.

No punitive fees. Cities cannot impose impact fees or utility connection fees on an ADU greater than those imposed on other single-family dwellings.

No tiny size caps. Cities cannot limit an ADU to less than 1,000 square feet or 75 percent of the size of the primary dwelling.

No owner-occupancy requirement. This is the big one for anyone thinking about rental income. Cities can no longer require that you live in either the primary dwelling or the ADU. Under the prior law, internal ADUs had an owner-occupancy condition. That's gone at the city level.

No height discrimination. Cities cannot cap ADU height below the height of the existing primary dwelling on the lot.

No general discrimination. Cities cannot impose restrictions on ADUs that are more restrictive than restrictions on single-family dwellings in the same zoning district with regard to setbacks, lot size, coverage, or building frontage.

Notice what is not on that list: a specific setback number. The introduced bill had a four-foot side and rear setback rule. It was removed. What survives is parity, meaning whatever your zone requires for a house is the ceiling for what it can require of your ADU.

Do I still have to go through a hearing?

No, and this provision may matter more than any of the numbers.

Projects that meet the jurisdiction's established land use requirements must be approved administratively and as a matter of right, without the need for discretionary approval. The law further requires that any approval standards, special conditions, and procedures a local government adopts be clear and objective, and that they not have the effect, either singly or cumulatively, of discouraging ADU development through unreasonable cost or delay.

In plain terms: if your project meets the written rules, it gets approved over the counter. No public hearing where a neighbor can talk the commission out of it. No design review that functions as a veto.

That's a real shift. Discretionary review has historically been how ADUs died quietly.

What about my HOA?

This is the part with the widest reach, because the HOA provision is not limited to cities over 10,000. It applies statewide.

SB 1354 amended Idaho Code 55-3212 so that no homeowner's association may add, amend, or enforce any covenant, condition, or restriction in a way that limits or prohibits accessory dwelling units, unless the owner of the affected property expressly agrees in writing.

The inclusion of the word "enforce" is significant. Prior law focused on newly added covenants. This language reaches enforcement of existing ones.

HOAs retain some authority. They may adopt reasonable rules governing the use of internal ADUs, including architectural design consistent with the primary dwelling, size limits, height limits, setback requirements, open space requirements, parking controls, and bedroom requirements. And the law does not disturb valid covenants restricting a property owner's right to transfer an interest in land where that covenant already applied when the owner acquired the property. Short-term rentals are handled separately under a different statute.

Here's my honest read, and I want to be careful. This language is new and untested. Idaho's appellate courts have not yet interpreted it, and there's real tension between a blanket prohibition on enforcement and an HOA's ability to impose "reasonable rules." If you're in an HOA with a recorded ADU prohibition, do not assume it's simply void, and do not assume it's simply enforceable either. That's a question for an Idaho real estate attorney, not for your builder and not for a blog post.

Has Twin Falls updated its code yet?

Not for this, and there's an irony in the timing.

The City of Twin Falls adopted an entirely new zoning code, Title 10, effective January 1, 2026. SB 1354 was signed March 31, 2026. So Twin Falls rewrote its zoning code roughly three months before the law that requires it to rewrite parts of that code again.

The city has until February 1, 2027.

What that means for you right now, in the gap: the prohibition on banning ADUs took effect July 1, 2026, and it applies regardless of whether the city has finished amending its code. A city cannot enforce a ban simply because its ordinance still contains one on paper. But the affirmative requirements, the specific size floors and parking prohibitions and so on, are things cities are obligated to write into their regulations by February.

Practically, that means anyone applying between now and next February may run into a counter that hasn't fully caught up. Come prepared. Know what the statute says. And expect the ground to keep shifting a bit until the amendments land.

What the law does not change

This is the section I'd most want you to read, because the statute has an entire subsection dedicated to what it does not override, and in this valley those carve-outs are frequently the actual obstacle.

The law does not supersede state or local laws protecting public health, safety, and welfare, including:

1. Building codes, fire safety standards, and flood plain regulations
2. Laws regarding water, sewer, storm drainage, road access, and utility services necessary to support the required density
3. Laws regarding environmental hazards, aquifer recharge zones, steep slopes, and critical habitat protections
4. Setback requirements for rights-of-way and easements

Let me translate that into what it means on an actual Magic Valley lot.

Your septic system is probably the real constraint. Adding a second full dwelling with its own kitchen and bathroom means additional wastewater load. If you're on septic, that's a South Central Public Health District question, and it's entirely untouched by SB 1354. A drainfield sized for a three bedroom house does not automatically absorb an ADU. This is the single most common reason an ADU plan stops in this area, and it has nothing to do with zoning.

Water matters too. On a private well, capacity and water rights are real questions. On city water, connection sizing is a real question.

Building code still applies in full. Your ADU is a dwelling. It needs egress, ceiling height, smoke and carbon monoxide alarms, energy compliance, and inspections, exactly like any other habitable space. If you're converting a basement into an internal ADU, everything in our basement guide applies.

Easements still bind. The law explicitly preserves right-of-way and easement setbacks. Check your plat before you pick a spot in the yard.

And you still need permits. Which office issues them depends on your address, and inside Twin Falls city limits that's a different process than out in the county. Our permits guide walks through that.

Is an ADU actually the right move?

Separate question from whether it's legal, and worth asking honestly.

An ADU makes sense when you need a genuinely separate living space: a parent who needs proximity but not the same kitchen, an adult kid coming back, a rental unit, or a guest space that gets used often enough to justify a full build.

An addition usually makes more sense when what you actually need is more house. Additions share systems with the existing home, which is generally cheaper per square foot than building a second self-contained dwelling with its own kitchen, bathroom, heating, and service connections.

An ADU carries a second of nearly everything. That's the cost driver, and it's why the honest comparison isn't ADU versus nothing, it's ADU versus addition versus doing neither.

Worth knowing there's a companion bill, SB 1353, dealing with twin homes and duplexes on single-family lots. Different statute, similar structure. If your interest is rental income rather than family housing, that's another avenue to look into.

Thinking about an ADU or guest home?

We build ADUs, guest homes, and additions across Twin Falls, Jerome, Kimberly, Buhl, Filer, Burley, Rupert, and unincorporated Twin Falls County. We'll tell you straight whether your lot can support one, what your septic can actually handle, whether SB 1354 applies at your address, and whether an addition would serve you better.

We're a registered Idaho contractor, RCE-65510, insured and warrantied. One point of contact, a real itemized estimate, and an honest answer even when the answer is that this isn't the right project.

Tell us what you're planning → or call (208) 731-1729

I'm a builder, not an attorney. This is a plain-English summary of a new statute, and new statutes get interpreted. For anything involving an HOA dispute or real money at stake, talk to an Idaho attorney.

Frequently asked questions

Can my city still ban ADUs? Not if it has a population over 10,000. Since July 1, 2026, no Idaho city may enact or enforce an ordinance banning accessory dwelling units in any residential zoning area. Cities under 10,000, and counties, are not covered by this law and may still restrict or prohibit them.

Does SB 1354 apply in Kimberly, Buhl, or Filer? No. All three are well under the 10,000 population threshold. In our service area only Twin Falls, Jerome, and Burley are covered. If you read that the threshold is 5,000, that was the bill as introduced, before the Senate amended it.

What if I live outside city limits? The law does not apply to counties at all. In unincorporated Twin Falls County, your ability to build an ADU depends entirely on county zoning, and the state has not granted you a protected right.

Can I build both an internal and a detached ADU? Not as a matter of right. The enacted law requires cities to allow either one internal ADU within the single-family dwelling or one detached ADU per lot. Some coverage says both, because the original bill said both. That language was amended before passage. A city is free to be more permissive if it chooses.

Do I have to live on the property? No. Covered cities can no longer impose an owner-occupancy requirement on either the primary dwelling or the ADU. That's one of the most significant changes from prior law.

How big can my ADU be? Cities cannot limit an ADU to less than 1,000 square feet or 75 percent of the size of the primary dwelling. Your city may allow more but cannot cap you below that floor.

Will I need a public hearing? No, if your project meets the jurisdiction's established land use requirements. Those projects must be approved administratively and as a matter of right, without discretionary approval. Standards a city adopts also have to be clear and objective, and cannot discourage ADUs through unreasonable cost or delay.

Can my HOA stop me? The amended statute says no HOA may add, amend, or enforce a covenant that limits or prohibits ADUs unless the owner expressly agrees in writing, and unlike the zoning provisions, this applies statewide. But HOAs may still adopt reasonable rules on things like architectural design, size, height, setbacks, and parking for internal ADUs. This language is new and hasn't been tested in Idaho's appellate courts, so if you're facing an HOA prohibition, get legal advice rather than assuming.

When do cities have to update their codes? By February 1, 2027. The ban on prohibiting ADUs already took effect July 1, 2026, so a city cannot enforce a ban in the meantime just because its written code hasn't caught up.

Does this mean my septic can handle an ADU? No, and this is where most ADU plans in the Magic Valley actually stop. The law explicitly does not supersede laws regarding water, sewer, and utility services necessary to support the density. An additional dwelling with its own kitchen and bathroom adds wastewater load, and that's a South Central Public Health District question. Get it answered before you spend money on design.

Do I still need a building permit? Yes. An ADU is a dwelling and the full building code applies, including egress, ceiling height, alarms, and energy compliance. Which office issues the permit depends on whether your address is inside city limits.

Is an ADU cheaper than an addition? Usually not per square foot. An ADU is a second self-contained dwelling with its own kitchen, bathroom, heating, and service connections. An addition shares those with the existing house. If what you need is more house rather than a separate residence, an addition is often the better value.

Sources: Idaho Senate Bill 1354, as amended (2026), Session Law Chapter 265; Idaho Code 67-6541 and 55-3212; Idaho Legislature bill records; U.S. Census Bureau population estimates via 2024 American Community Survey; City of Twin Falls Planning and Zoning. Verified August 2026. This is a new statute and local implementation is ongoing, so confirm current requirements with your city before relying on any of it.

Related: Building Permits in Twin Falls: A Homeowner's Guide · Finishing a Basement in Twin Falls · ADUs & Guest Homes