What Idaho's 2026 Housing Bills Mean for Twin Falls

TL;DR:

Idaho's 2026 legislative session produced the most significant housing reform in the state's history. Six bills passed covering ADUs, starter homes, manufactured housing, lot splits, single-stair apartments, and permitting speed. The two that matter most for Twin Falls homeowners are SB 1354 (ADUs by right, effective July 1, 2026) and SB 1352 (starter home subdivisions). Under SB 1354, Twin Falls must allow at least one ADU per single-family lot, cannot require owner-occupancy, cannot cap ADU size below 1,000 sq ft or 75% of the primary home, and cannot require off-street parking in most cases. The city has until February 1, 2027 to update its local codes. If you've been waiting for a clearer legal path to build an ADU, this is it.

If you've been hearing that Idaho "changed the rules" on ADUs and housing but aren't sure what actually passed, you're not alone. The 2026 legislative session moved fast, and the details matter more than the headlines. Some of what's circulating online is outdated, based on earlier draft versions of bills, or flat-out wrong.

This guide covers what actually became law, what it means specifically for Twin Falls homeowners, and what hasn't changed. Every claim below is sourced from the enacted bill text, legislative reporting from BoiseDev, and the Sightline Institute's comprehensive analysis of Idaho's 2026 housing legislation.

The Big Picture: Six Bills, One Goal

Idaho's legislature passed six housing bills in 2026, all aimed at increasing housing supply in cities with populations over 10,000. Twin Falls clears that threshold, so all of these apply. The Sightline Institute called it "one of the biggest housing affordability coups of any US state to date," comparing it to Washington's "year of housing" and Montana's "housing miracle."

Here's what passed:

SB 1354: ADUs by right. Cities must allow at least one ADU per single-family lot and cannot use zoning to block them.

SB 1352: Starter home subdivisions. Cities cannot ban high-density starter home developments on land of four acres or more. Lot sizes as small as 1,400 to 1,500 sq ft are protected, with up to 12 units per acre.

SB 1353: Manufactured homes. Cities cannot ban manufactured homes in residential zones through zoning restrictions.

HB 800: Lot splits. An administrative path for limited lot splits on properties with an existing or approved ADU, enabling separate ownership or financing.

HB 706: Single-stair apartments. Cities can now choose to allow small apartment buildings (up to six stories) served by a single interior staircase, which reduces construction costs and enables more natural light and cross-ventilation.

Permitting shot clock. Cities face new time limits on permit review to prevent indefinite delays.

For ADU-focused homeowners in Twin Falls, the two that matter most are SB 1354 and HB 800. Let's break those down.

SB 1354: What It Actually Says About ADUs

Senate Bill 1354 was signed by Governor Brad Little on March 31, 2026, and takes effect July 1, 2026. It is codified at Idaho Code Section 67-6541. The bill passed the Senate 25 to 10 and the House 47 to 23.

What cities can no longer do

Under SB 1354, Twin Falls (and every Idaho city over 10,000) cannot:

Ban ADUs. Cities cannot enact or enforce any ordinance that prohibits accessory dwelling units in residential zones.

Require owner-occupancy. The old requirement that you live in the primary home to get an ADU permit is gone. This is explicitly prohibited. Rental property owners can now add ADUs without restructuring ownership.

Cap ADU size below 1,000 sq ft. Cities cannot limit your ADU to less than 1,000 sq ft or 75% of the primary dwelling's size, whichever is larger. For a 1,600 sq ft home, a city cannot require the ADU to be smaller than 1,200 sq ft. For a 2,000 sq ft home, the floor is 1,500 sq ft. You can build smaller if you choose, but the city cannot force it.

Require off-street parking. In most cases, cities cannot require additional parking for an ADU. Exceptions exist if the primary home has no off-street parking at all, or if the street is unpaved and not designed for on-street parking.

Charge ADU-specific impact fees. Impact fees and utility connection fees for ADUs cannot exceed what the city charges for other single-family dwellings.

Set stricter setbacks for ADUs. Setback rules for ADUs cannot be more restrictive than setback rules for single-family homes in the same zoning district.

Require discretionary approval. ADU projects that meet established requirements must be approved administratively, as a matter of right. No lengthy discretionary review process.

What cities can still do

SB 1354 preserves city authority over building codes, fire safety, health and safety standards, floodplain regulations, water and sewer standards, and environmental hazard regulations. The law removes zoning barriers, not safety standards.

Properties in designated historic districts are exempt from SB 1354's requirements.

The compliance timeline

Cities have until February 1, 2027 to update their codes. The law takes effect July 1, 2026, so there will be a transition period where the state law is active but some cities haven't yet revised their local codes. If you're planning a project during that window, check with the Twin Falls Planning and Zoning Department for the current local status.

How SB 1354 Changes Things in Twin Falls Specifically

The Twin Falls Uniform Development Code has several ADU rules that will need to be reconciled with SB 1354 once the city updates its codes. Here's where the state law and the current city code differ:

Size cap. The current city code limits ADUs to 45% of the principal residence's living space. SB 1354 sets the floor at 1,000 sq ft or 75%, whichever is larger. For most Twin Falls homes, this is a significant increase in what you're allowed to build. The city will need to revise this provision.

Parking. The current city code requires one additional parking space for the ADU. SB 1354 eliminates off-street parking requirements in most cases. This provision will likely change.

Shared utilities. The current city code requires ADUs to share water, sewer, and sanitation with the primary dwelling, with no separate meters. SB 1354 doesn't specifically address this, so the shared-utility rule may remain. However, the provision that ADU impact fees cannot exceed those for other single-family homes may affect how connection charges are handled.

Design matching. The current code requires ADUs to match the primary home's roof pitch, siding, and windows. SB 1354 doesn't specifically override design standards, so this requirement may stay in place. The law does prohibit standards that "cumulatively discourage ADU development through unreasonable cost or delay," so overly burdensome design requirements could potentially be challenged.

What About HOAs?

SB 1354 strengthens HOA protections beyond what HB 166 (2023) offered. Here's how it works now:

HOAs cannot add, amend, or enforce any covenant that limits or prohibits ADUs unless the affected property owner expressly agrees in writing. However, covenants that existed when you purchased your property remain enforceable. HOAs can still adopt reasonable rules on architectural design, size, height, setbacks, parking, and bedroom counts.

The practical takeaway: If you bought your home after the law takes effect and your HOA's CC&Rs don't already ban ADUs, the HOA cannot block you. If the ban was in your CC&Rs when you purchased, it can still be enforced. Review your documents carefully.

This is a significant upgrade from HB 166, which only protected internal ADUs (basement, attic, garage conversions) on owner-occupied properties. SB 1354 extends protection to detached ADUs and removes the owner-occupancy requirement.

HB 800: Lot Splits for ADU Properties

This bill creates an administrative path for homeowners to split their lot if they have an existing or approved ADU. The split enables separate ownership or financing of the ADU portion, which opens up new possibilities:

You could sell the ADU as a standalone property. You could finance the ADU separately from the primary home. A buyer could purchase your home and the ADU as two separate transactions.

The split is limited: it doesn't add new density beyond what zoning already allows, and each resulting lot must still meet local infrastructure, setback, and building requirements. It's a "one and done" provision, meaning you can't split the same parent parcel repeatedly.

For Twin Falls homeowners, this is significant because it means an ADU isn't just a rental unit anymore. It can become a separately owned piece of real estate, which fundamentally changes the investment math.

SB 1352: Starter Homes (The Other Bill Worth Knowing)

While SB 1354 covers ADUs, SB 1352 addresses the broader housing supply problem. It prevents cities from banning "starter home subdivisions" on land of four acres or more and requires cities to allow lot sizes as small as 1,400 to 1,500 sq ft, with a maximum density of 12 homes per acre.

This doesn't directly affect ADU homeowners, but it signals the broader direction Idaho is heading: more housing types, smaller lots, fewer zoning barriers. If you're thinking about building an ADU on a smaller lot in Twin Falls, the legislative wind is at your back.

What This Means If You're Planning an ADU in Twin Falls

If you've been on the fence about building, here's what's changed in your favor:

The legal path is clearer. After July 1, 2026, Twin Falls cannot use zoning to block your ADU project if it meets established standards. After February 1, 2027, the city's local codes must be updated to comply.

Size restrictions are more generous. The jump from 45% of principal residence (current city code) to 1,000 sq ft or 75% (state law) means most homeowners can build a significantly larger unit than what was previously allowed.

No owner-occupancy requirement. Investors and homeowners who don't live on the property can now add ADUs. This opens the door for rental property owners across the Magic Valley.

Parking is simplified. If your home already has off-street parking, the city generally can't require additional spaces for the ADU.

HOA barriers are reduced. Unless your CC&Rs already prohibited ADUs when you purchased, your HOA can't add that restriction now.

What Hasn't Changed

You still need a building permit. SB 1354 gives you the right to build, but it doesn't eliminate the permitting process. Plans, inspections, and code compliance are still required.

Building codes still apply. Fire safety, structural standards, energy codes, and mechanical/electrical/plumbing requirements are all unchanged.

Your lot still has physical constraints. Setbacks, lot coverage, utility capacity, drainage, and access all still matter. The law changes what's legally allowed, not what's physically possible on your specific property.

The city code hasn't been updated yet. Between now and February 1, 2027, there may be friction between the new state law and the old city code. A feasibility check can help you navigate that transition.

Frequently Asked Questions

Does SB 1354 apply to Twin Falls?

Yes. Twin Falls has a population over 10,000 and is inside city limits. The law takes effect July 1, 2026, with a city compliance deadline of February 1, 2027.

Can I build two ADUs on my lot?

No. SB 1354 protects one ADU per single-family lot. It can be either an internal unit (within the primary home or garage) or one detached structure in the rear yard. Not both.

How big can my ADU be now?

The city cannot limit your ADU to less than 1,000 sq ft or 75% of your primary home's size, whichever is larger. You can build smaller if you choose.

Does this override my HOA?

It depends on when you bought and what your CC&Rs say. If your HOA already had an anti-ADU covenant when you purchased, it can still be enforced. If not, the HOA cannot add one to block you. Review your specific documents.

Do I still need to live on the property?

No. SB 1354 explicitly prohibits owner-occupancy requirements for ADUs.

Can I rent the ADU on Airbnb?

SB 1354 doesn't specifically address short-term rentals. However, Idaho HB 583 (also signed in 2026, effective July 1) establishes sweeping protections for short-term rentals statewide. Our guide to Airbnb and ADUs in Twin Falls covers this in detail.

What's the first step?

A feasibility check on your specific property. The new laws change what's legally allowed, but your lot's physical constraints (setbacks, utilities, site conditions) still determine what's actually buildable. That's where every project should start.

The 2026 legislative session gave Twin Falls homeowners the clearest legal path to building an ADU that Idaho has ever had. If you've been waiting for the rules to catch up with the opportunity, they just did. Reach out to Twin Falls ADU Guys for a feasibility check, and we'll tell you exactly what your property can support under the new law.