Researching ADU regulations in Idaho is not always straightforward. Requirements can vary significantly from city to county, and while some statewide guidance exists, many rules around size, placement, and design are determined at the local level.
Accessory dwelling units play an important role for many families, from housing aging parents to creating affordable options for young adult children. We don’t want regulatory complexity to stand in the way of the home you need. That is why we created this guide covering ADU regulations across Idaho, including all 44 counties and 10 major cities, so you can find local requirements or evaluate potential locations in one place.
Zook Cabins is here to support you throughout your ADU journey. If you have questions or are ready to explore your options, request a quote or contact our team.
Are ADUs Allowed in Idaho?
Yes. While requirements vary by city and county, the state has adopted House Bill 166, which prohibits jurisdictions from imposing an outright ban on accessory dwelling units. This creates a generally ADU-friendly environment throughout the state. Since local standards still apply, it is crucial to confirm specific requirements with your city or county officials.
ADUs That Are Allowed in Idaho
In Idaho, ADU size limits typically range from 500 to 1,200 square feet. Because requirements can vary significantly by county and city, it is important to confirm local standards with the officials listed below. That said, if ADUs are permitted in your area, all of the models below generally fall within this size range.
A-Frame ADU
The Grove ADU
The Luna ADU
The Rivara ADU
The Sonoma ADU
What Is Considered An ADU in Idaho?
ADU regulations in Idaho vary significantly depending on the location. Under House Bill 166, jurisdictions cannot impose an outright ban on attached accessory dwelling units, which means attached structures and garage conversions are typically allowed. Some areas also permit detached ADUs, while others do not. In certain jurisdictions, recreational vehicles or tiny homes on wheels may also qualify as ADUs.
Because a wide range of structures can potentially serve as an ADU, the sections below break down which options are allowed across Idaho in greater detail.
Can Park Model Tiny Homes Be Used As ADUs?
Yes and no. Park model tiny homes are typically built to ANSI 119.5 standards and are RVIA certified, which classifies them as recreational vehicles. Because of this, some jurisdictions prohibit RVs from being used as accessory dwelling units, like Idaho Falls. While other areas, such as Blaine County, do allow park model units to function as ADUs.
Because rules vary by location, refer to the city and county sections of this article to confirm local requirements. You can also review our guide to tiny home regulations in Idaho to see where these units are permitted more broadly.
For a deeper breakdown of the differences between ADUs and tiny homes, see our comprehensive comparison guide.
Can Log Cabins Be Used As An ADU?
Yes, they can, as long as they meet local size, placement, and other applicable ADU requirements. In Idaho, ADU size limits typically range from 500 to 1,200 square feet. As a result, models like Zook Cabin’s Lariat and Wrangler, which start in the 600 to 700 square foot range, are typically permitted. Larger models may also be allowed, depending on the specific standards in your area.
Can Modern Cabins Be Used As An ADU?
Yes, depending on location, modern cabins may also be permitted for use as accessory dwelling units. It is essential to verify with local officials that a modern cabin complies with applicable size, placement, and design standards.
In Idaho, ADU size limits typically range from 500 to 1,200 square feet. This broad range means many modern cabins, including those offered by Zook Cabins, can be well-suited for use as ADUs where permitted.
What is the Difference Between a Prefab ADU & a Modular ADU?
The difference comes down to construction and delivery.
Prefab ADUs are built entirely in a factory and delivered to your property fully finished and ready for placement.
Modular ADUs are constructed in sections in the factory and then fully assembled on site after delivery.
For a closer comparison of how these two options differ, refer to our guide on prefab and modular ADUs.
What is the Minimum Size for an Accessory Dwelling Unit?
Most areas do not impose a minimum size requirement for ADUs. Instead, they typically require compliance with minimum building code standards for a dwelling unit. To ensure all sizing requirements are met, please confirm the details with your local officials listed below.
Can My ADU be Bigger Than My House?
No, most areas require that an ADU remain a certain percentage of the primary residence’s livable area and does not exceed the height of the primary residence.
Do You Need a Permit For An ADU in Idaho?
Yes, adding an accessory dwelling unit typically requires a building permit or a permit specific to the ADU. Additional approvals may also be needed, including zoning clearance and permits for electrical, plumbing, or HVAC work. Some areas may also require special or conditional use permits. To ensure that all necessary permits are obtained, please contact the city or county officials listed below.
Are There Any Incentives or Grants for ADUs in Idaho?
Idaho does not offer broad statewide incentives or grants for accessory dwelling units, but some cities, such as Hailey, provide local incentives. To determine if ADU incentives are available in your area, please contact the local officials listed below.
What Features are Included in An ADU from Zook Cabins?
While features vary by model, our ADUs are designed with modern style and flexible layouts, making it easy to choose a floor plan that fits your needs. Available options include:
- Fully finished interiors
- Multiple bedroom and bathroom layouts
- Sizes ranging from 571 to 848 square feet
- Heating and cooling options
- High quality insulation
- Optional front porches or loft spaces
- Bright living areas with abundant natural light
Ready to explore what a Zook Cabins ADU could look like on your property? Connect with one of our sales representatives to get started.
Are Zook Cabin’s ADUs Built to Code?
Yes. Our models are designed to meet local size and room requirements and comply with applicable building codes. As modular homes, they are installed on permanent foundations, and our team will help you select the foundation type that best fits your property and local regulations.
Can an ADU Have Multiple Bedrooms and Bathrooms?
Yes, but it largely depends on location. Some cities and counties limit ADUs to one bedroom, while others allow two. For example, Ada County permits only one bedroom, while the City of Boise allows up to two. Because requirements vary, it is important to confirm local standards with your city or county officials before planning.
If you are in an area like Boise that permits two bedrooms, models such as the Luna, A-Frame, and Grove from Zook Cabins offer two-bedroom layouts. In areas limited to one bedroom, options like the Rivara or Sonoma are one-bedroom units.
Are ADUs A Good Investment?
Accessory dwelling units are often permitted as long-term rental properties, depending on local regulations, which can provide a meaningful return on investment and ongoing rental income. Some jurisdictions also permit ADUs to be used as short-term rentals, although this is less common and typically subject to stricter regulations.
In many cases, properties with an ADU also sell for more than comparable homes without one, adding long-term value beyond rental income.
Outside of financial benefits, ADUs are a practical solution for housing aging parents or young adult children. Instead of relying on costly dorm housing, assisted living, or off-site rentals, an ADU allows you to keep family close while maintaining privacy and independence.
If you are considering an ADU investment, contact us to learn more or request a free quote on any of the models listed above.
What Are the Requirements for ADUs in Each County in Idaho?
Below are the requirements for all 44 counties in Idaho regarding ADUs. While some have clearly defined ADU regulations, others are unclear. It’s important to note that rules vary depending on the city and county in which you live. For more specific guidance relevant to your area, skip ahead to the city section of this article.
Does Ada County, Idaho, Allow ADUs?
Yes, the county does allow ADUs, provided that the following requirements are met:
- Maximum Size: 20% of the lot area
- Maximum Number of Bedrooms: 1
In addition, the property must comply with the dimensional standards of the applicable land use district. For details on specific zoning requirements, contact Development Services.
Does Adams County, Idaho, Allow ADUs?
There are no county-level ADU standards in place at this time. Regulations are handled by individual cities. For details on what is allowed in your area, refer to the city section below.
Does Bannock County, Idaho, Allow ADUs?
Yes, but the county does not permit traditional accessory dwelling units. Instead, it allows what it defines as accessory cottage dwellings. These structures cannot be rented or occupied for financial gain and are limited to use by aging parents or adult children.
Approval through the permit application process is required. The county enforces specific building standards as part of this review. For additional details, contact the Planning and Development Department.
Does Bear Lake County, Idaho, Allow ADUs?
The county allows ADUs, but detailed standards are not clearly defined. To confirm eligibility and determine the applicable requirements for your property, contact the Building Department.
Does Benewah County, Idaho, Allow ADUs?
The county does not have established standards for accessory dwelling units. However, cities or towns can enforce their own regulations. For clear guidance on what is allowed in Benewah County, contact your local officials or the Building Department.
Does Bingham County, Idaho, Allow ADUs?
Yes, one accessory dwelling unit is allowed per property with an approved building permit. The permit confirms compliance with the following requirements:
- Minimum Lot Size: 2 acres (unless a conditional use permit is obtained)
- Maximum ADU Size: 50% of the gross floor area of the principal structure (unless a conditional use permit is obtained)
Additional standards may apply. For confirmation of all requirements and permit approval, contact the Planning & Development Department.
Does Blaine County, Idaho, Allow ADUs?
Yes, Blaine County allows both accessory dwelling units and tiny homes on wheels classified as ADUs. One may be permitted if the following requirements are met:
- Maximum Size: 1,200 square feet
- Minimum Size: Must meet Appendix Q of the IRC standards for tiny homes
ADUs must also meet zoning setback standards and receive a building permit. For confirmation of all requirements and permit approval, contact Building Services.
Does Boise County, Idaho, Allow ADUs?
Yes, but they must meet the following standards:
- Maximum Size: 900 square feet or 70% of the total floor area of the primary structure, whichever is less.
- Maximum Number of Bedrooms: 2
ADUs must comply with the standards of the applicable zoning district and the building code. For confirmation of all requirements, contact the Planning and Zoning Department.
Does Bonner County, Idaho, Allow ADUs?
Bonner County outlines the following standards for ADUs:
- Maximum Size: 900 square feet
- Maximum Number of Bedrooms: 2
ADUs are subject to the same setback requirements as the primary residence. Lots smaller than 20,000 square feet are limited to attached ADUs only. For confirmation of compliance with all applicable standards, contact the Planning Department.
Does Bonneville County, Idaho, Allow ADUs?
There are no clearly defined county-level regulations in place. For clarification on what is allowed, contact the Planning and Zoning Department. In most cases, cities and towns enforce their own requirements, so it is also important to check with local officials.
Does Boundary County, Idaho, Allow ADUs?
In 2023, the county considered ADU legislation that would allow one unit per property with a maximum size of 1,050 square feet. It is unclear whether this proposal was adopted. For the most up-to-date information on current ADU regulations, contact the Planning and Zoning Department.
Does Butte County, Idaho, Allow ADUs?
Current county-level ADU allowances are not clearly defined. For guidance on what is permitted, contact the Planning and Zoning Department.
Does Camas County, Idaho, Allow ADUs?
Yes, the county allows what it defines as additional dwelling units. No explicit size limits are outlined. For clarification on applicable requirements, contact the Building Department.
Does Canyon County, Idaho, Allow ADUs?
Canyon County does not have county-level ADU requirements in place. Many local jurisdictions, including Caldwell and Nampa, allow ADUs. For confirmation of applicable requirements, contact the Building Department.
Does Caribou County, Idaho, Allow ADUs?
Yes, accessory dwelling units are permitted. Beyond the requirement for a kitchen, bathroom, and separate entrance and exit, additional county-level standards are unclear. For clarification on what is allowed, contact the Building Department.
Does Cassia County, Idaho, Allow ADUs?
Cassia County does allow ADUs under the following conditions:
- Minimum Size: 300 square feet
- Maximum Size: 1,000 square feet
- Minimum Lot Size: 1 acre
A building permit is required before construction or occupancy begins. For confirmation of all requirements and permit approval, contact the Building Department.
Does Clark County, Idaho, Allow ADUs?
Accessory dwelling units are referenced in the county code, but specific standards for their construction are not clearly defined. For clarification on applicable requirements, contact the Planning and Zoning Department.
Does Clearwater County, Idaho, Allow ADUs?
The county code does not currently address accessory dwelling units. For guidance on what may be allowed, contact the Building and Planning Department.
Does Custer County, Idaho, Allow ADUs?
Yes, accessory dwelling units are allowed. For specific construction standards and requirements, contact the Planning and Zoning Department.
Does Elmore County, Idaho, Allow ADUs?
Yes, Elmore County allows one accessory dwelling unit up to 900 square feet with administrative approval. For confirmation of requirements and approval details, contact the Building Department.
Does Franklin County, Idaho, Allow ADUs?
Franklin County does not have clearly defined ADU standards in place at this time, but accessory dwelling units are not outright prohibited. For clarification on current regulations, contact the Planning and Zoning Department.
Does Fremont County, Idaho, Allow ADUs?
County-level regulations are not clearly defined. For guidance on what is allowed, contact the Building Department or your local officials.
Does Gem County, Idaho, Allow ADUs?
Gem County allows accessory dwelling units subject to the following standards:
- Maximum Size: 1,800 square feet
- Distance from the Primary Dwelling: No more than 200 feet and no less than 10 feet
Additional standards may apply. For confirmation of all requirements and permit approval, contact the Planning and Zoning Department or your local officials.
Does Gooding County, Idaho, Allow ADUs?
There are currently no clear ADU regulations in place. For clarification on what is allowed, contact the Building Department.
Does Idaho County, Idaho, Allow ADUs?
Idaho County does not currently outline specific requirements for accessory dwelling units. Regulations may be handled at the local level, so it is essential to check with your city or town officials.
Does Jefferson County, Idaho, Allow ADUs?
Yes, accessory dwelling units are permitted and must meet the following standards:
- Maximum Size: 1,200 square feet
- Number of Bedrooms: 2
ADUs must also comply with zoning district setback requirements. For confirmation of all applicable standards, contact the Planning, Zoning, and Building Department.
Does Jerome County, Idaho, Allow ADUs?
There are no outlined requirements for ADUs at the county level at this time. For more information on what is allowed, contact the Building Department.
Does Kootenai County, Idaho, Allow ADUs?
Yes, the county allows what it defines as an accessory living unit, limited to the greater of 1,000 square feet or 50 percent of the primary dwelling’s living area. A permit is required. Permitting information is available through the Building Department.
Does Latah County, Idaho, Allow ADUs?
Yes, accessory cottage housing is allowed, with a maximum size of 900 square feet or 50 percent of the primary dwelling’s total square footage. Additional standards for placement, setbacks, and design apply. For confirmation of all requirements, contact the Building Department.
Does Lemhi County, Idaho, Allow ADUs?
Lemhi County does not have clearly defined standards for accessory dwelling units. To confirm what may be allowed, contact the Building Department.
Does Lewis County, Idaho, Allow ADUs?
The county building and zoning code currently makes no mention of accessory dwelling units. To confirm what may be allowed, contact the Planning and Zoning Department.
Does Lincoln County, Idaho, Allow ADUs?
Yes, provided that it aligns with the following standards:
- Number of Bedrooms: 2
- Maximum Size: 700 square feet
A building permit must be obtained from the Planning and Zoning Department. Contact them before beginning your ADU project.
Does Madison County, Idaho, Allow ADUs?
The county may permit them, but specific information is unavailable. For more information on what they currently permit, contact the Building Department.
Does Minidoka County, Idaho, Allow ADUs?
Yes, accessory dwelling units are permitted; however, the county code does not outline specific standards, such as room counts or maximum square footage. It is essential to verify the applicable requirements with the Building and Zoning Department before commencing construction.
Does Nez Perce County, Idaho, Allow ADUs?
Yes, the county allows accessory apartments, which function as attached accessory dwelling units. The code does not clearly indicate if detached units are permitted. For confirmation of what is currently allowed, contact the Planning and Building Department.
Does Oneida County, Idaho, Allow ADUs?
Yes, but specific standards are not clearly defined. For guidance on size, setback, and placement requirements, contact the Planning and Zoning Department.
Does Owyhee County, Idaho, Allow ADUs?
The county code currently makes no mention of ADUs. For more information on what’s currently allowed, contact the Building Department.
Does Payette County, Idaho, Allow ADUs?
Payette County allows accessory dwelling units up to a maximum size of 1,500 square feet with an approved permit. To confirm applicable requirements and permit approval, contact the Planning and Zoning Department.
Does Power County, Idaho, Allow ADUs?
The county code does not currently outline any standards for ADUs. As a result, you should check with the Building Department to determine what is allowed.
Does Shoshone County, Idaho, Allow ADUs?
It’s unclear if they are allowed. For more information on current county ADU regulations, contact the Planning and Zoning Department.
Does Teton County, Idaho, Allow ADUs?
Yes, Teton County allows accessory dwelling units up to 1,500 square feet with an approved building permit. Additional requirements apply and vary by zoning district. For confirmation of all applicable standards, contact the Building Department.
Does Twin Falls County, Idaho, Allow ADUs?
The county code currently does not address accessory dwelling units. For clarification, contact the Planning Department at 208-734-9490.
Does Valley County, Idaho, Allow ADUs?
Yes, accessory dwelling units are allowed with an approved permit from the Planning and Zoning Department. The ADU must not exceed 1,000 square feet or 50 percent of the primary residence’s square footage, whichever is less.
Does Washington County, Idaho, Allow ADUs?
It is unclear what the county allows, as its code does not mention ADUs. For more information, contact the Planning and Zoning Department.
Find Your Accessory Dwelling Units Requirements in Idaho By Municipality
Below is an overview of accessory dwelling unit requirements for several major cities in Idaho. Because cities and towns often enforce their own regulations, it is crucial to confirm applicable requirements with local officials.
Does Boise, Idaho, Allow ADUs?
Yes, the city outlines the following requirements for accessory dwelling units:
- Maximum Size: 900 square feet or 70% of the primary dwelling’s total floor area
- Number of Bedrooms: 2
ADUs must comply with applicable building and zoning code requirements. For confirmation of compliance, contact Planning and Development Services.
Does Meridian, Idaho, Allow ADUs?
You can have an ADU in Meridian with a permit from the Community Development Department. The permit certifies that the following requirements are met:
- Maximum Size: 900 square feet or 50% of the primary dwelling, whichever is less.
- Number of Bedrooms: 2
It’s essential to contact the Community Development Department to ensure all requirements are met.
Does Nampa, Idaho, Allow ADUs?
Yes, you can have an ADU in Nampa, provided that it is no larger than 500 square feet, and a permit is obtained from the Planning and Zoning Department.
Does Idaho Falls, Idaho, Allow ADUs?
Yes, Idaho Falls adopted legislation in 2022 allowing accessory dwelling units subject to the following standards:
- Maximum size: 750 square feet
- Rear setback: 12 feet
- Recreational vehicles are permitted for use as ADUs
ADUs must also comply with placement standards for the applicable zoning district. For confirmation of all requirements, contact Community Development Services.
Does Pocatello, Idaho, Allow ADUs?
Yes, accessory dwelling units are allowed and must meet the following standards:
- Maximum Size: 750 square feet
- Number of Bedrooms: 1
The ADU must be similar in height and design to the primary residence and comply with zoning district placement standards. For confirmation of all applicable requirements, contact the Planning and Development Department.
Does Coeur d’Alene, Idaho, Allow ADUs?
ADUs are allowed in Coeur d’Alene with an approved permit and must meet the following standards:
- Minimum Size: None
- Maximum Size: 800 square feet; no more than 75% of the total square footage of the primary dwelling
- Setbacks:
- Front: 20 feet
- Side, Interior: 5 feet
- Side, Street: 10 feet
- Rear: 25 feet
For questions about ADU requirements, permit eligibility, or compliance, contact Building Services.
Does Twin Falls, Idaho, Allow ADUs?
The city code does not currently address accessory dwelling units or related requirements. For clarification on what may be allowed, contact the Planning and Zoning Department.
Does Post Falls, Idaho, Allow ADUs?
Post Falls allows accessory dwelling units (ADUs), subject to the following standard:
- Maximum size: No more than 50 percent of the primary residence’s living area or 1,000 square feet, whichever is less.
ADUs must also comply with zoning district placement requirements and match the design standards of the primary dwelling. For permit guidance and confirmation of requirements, contact the Community Development Department.
Does Lewiston, Idaho, Allow ADUs?
Lewiston allows accessory apartments subject to the following standards:
- Maximum size: 600 square feet or 30 percent of the primary residence’s habitable floor area, whichever is greater, with an absolute maximum of 900 square feet
- Maximum number of bedrooms: 2
- Maximum height: 18 feet for one-story structures or 28 feet for two-story structures
- Setbacks: 10 feet from the rear property line or 3 feet when abutting a rear alley
Accessory apartments must also comply with all zoning district setback requirements. For confirmation of compliance and permitting guidance, contact the Community Development Department.
Does Rexburg, Idaho, Allow ADUs?
The city code does not currently address accessory dwelling units, leaving permitted uses unclear. For clarification, contact the Planning and Zoning Department.
Searching For An ADU Builder Serving Idaho?
Now that you have navigated the legal requirements, you can focus on choosing an ADU builder who understands compliance and builds with intention. Working with a team that prioritizes quality, efficiency, and local regulations makes the entire process far easier and more predictable.
Zook Cabins is an ADU builder that helps homeowners bring compliant, well-built ADUs to life. We guide you through local requirements, help you find a unit that meets your needs, and handle the heavy lifting from start to finish so your ADU is a long-term investment you can feel confident about.
If you are ready to move forward or want guidance on next steps, request a quote, and let’s get started.
Tiny Home & ADU Rules By State: See How They Compare?
As noted earlier in this article, tiny homes may be allowed as ADUs in some areas and restricted in others. While ADUs and tiny homes share certain similarities, there are also important differences that can make choosing between the two less straightforward. If you want to explore tiny home requirements in Idaho or compare your options, review the states listed in the chart below to see how ADU and tiny home regulations differ.