Accessory Dwellings (ADU's) and other dwelling types

NOTE: This summary is very simplified, and is provided for informational purposes. Any questions on this topic should be directed to The Office of the Property Rights Ombudsman.

An Accessory dwelling unit, or “ADU,” generally refers to a complete secondary residential unit that can be added to a single-family residential lot. ADUs may be attached to or part of the primary residence, such as a basement apartment, or be detached as a separate building, such as a garage conversion or a standalone backyard structure.
In contrast, an Internal Accessory Dwelling Unit (“Internal ADU”), specifically, is a particular form of housing regulated by state law. Please see the dropdown for Internal ADU’s, below.

For the most part, state law delegates the authority of the state to regulate land use in general to local municipalities and counties, and allows local jurisdictions to enact their own zoning laws according to local policy and preference. But where the state legislature has directly spoken to a particular topic by legislation, state law controls and local land use regulations must conform with state law. See Utah’s Land Use, Development, and Management Act (LUDMA).

State law considers the allowance for internal or detached ADU’s in residential zones to be among the possible strategies for moderate income housing, and is included in a list of things a local government can include in its general plan to meet the required moderate income housing element. See Utah Code Sections 10-20-404 (for municipalities), and 17-79-403 (for counties).

Local land use regulations may both define and allow or prohibit ADU’s according to local ordinance. However, the ability to regulate Internal ADU’s is provided by state law, and local ordinances must comply with state law regarding Internal ADU regulations. See dropdown below.

An Internal Accessory Dwelling Unit (IADU or Internal ADU) is a particular kind of ADU that is regulated by state law. Specifically, it is defined to mean an ADU created within a primary dwelling for the purpose of offering a long-term rental of 30 consecutive days or longer; however, this only applies to a primary dwelling that is a detached, single-family home occupied as the primary residence of the owner of record, and where the IADU is within the footprint of the primary dwelling at the time the IADU is created. See Utah Code Sections 10-21-303 (for municipalities), and 17-80-303 (for counties).

State law provides that an IADU is a permitted use in any area zoned primarily for residential use in a county or municipality, subject to certain restrictions.

IADU’s must comply with all applicable building, health, and fire codes. However, construction of an Internal ADU is not subject to impact fees. See Utah Code Section 11-36a-202.

No IADU zones - A municipality can prohibit the creation of Internal ADU’s within a zoning district covering an area equivalent to 25% or less of the total area zoned primarily for residential use (or 67% or less for municipalities that have a university within its limits and a student population of 10,000 or more).

If enacted by ordinance, local governments may place certain restrictions on Internal ADU’s, including prohibiting IADU’s on lots smaller than 6,000 square feet, requiring that the IADU be designed so as to not change the appearance of the primary dwelling, requiring certain additional parking for the IADU, requiring a permit or license to rent an IADU, and/or prohibiting short-term rental (30 days or less) of IADU’s, among others. See Utah Code Sections 10-21-303 (for municipalities), and 17-80-303 (for counties).

Where an Internal ADU would not violate a local land use ordinance or building, health, or fire code, renting an Internal ADU may also not be prohibited by any private community association by CC&R or HOA rule.

Please contact the Ombudsman’s office if you have a particular question about Internal ADU’s.

While there is no comprehensive definition of what is considered a “tiny house” or “tiny home,” they are generally considered to be a single dwelling structure that is 400 square feet or less.

A tiny house might be built on-site similar to a traditional home. The State Construction Code has adopted specific building code standards that apply to tiny houses used as single dwelling units that are 400 square feet in area or less. See Utah Code Section 15A-2-103(1)(c) (adoption of Appendix Q of the 2018 edition of the International Residence Code).

Tiny houses, however, may also be considered modular units or manufactured homes depending on if they are either pre-built or built as sections that are delivered on-site to later be assembled. See Utah Code Section 15A-1-302.

Whether a tiny house or tiny home is permitted in any particular area will depend on local land use regulations, both how the structure is used (as a primary dwelling on a lot or as an accessory dwelling (see ADU’s, above), and the specifics of the structure, i.e., whether it is considered a modular or manufactured home.

State law provides some limits on regulating certain “building design elements” that might apply to tiny home construction. See Utah Code Sections 10-20-618 (for municipalities), and 17-79-614 (for counties). For example, cities/counties may not regulate “minimum building dimensions.” Id. They can, however, still enact a “minimum square footage” requirement that would serve to allow or prohibit tiny homes. Prohibited building design elements include a requirement for “minimum square footage over 1,000 square feet, not including a garage.” But as for minimums under 1,000 square feet, state law is silent, and appears to have left the discretion with local communities to either allow or restrict tiny homes via minimum square feet requirements.

A yurt is typically a membrane-covered structure that serves as a temporary dwelling and has no plumbing or electricity. Yurts or other kinds of temporary dwellings may be the subject of local land use regulations.

A “Remote yurt” under the State Construction Code is a yurt no larger than 710 square feet located in an unincorporated county area not zoned for residential, commercial, industrial or agricultural use, and set back at least 300 feet from any body of water.

Remote yurts must register with the local health department, but are otherwise generally exempted from permitting requirements of the state construction code, see Utah Code Section 15A-1-204, as well as fire code and Utah’s Water Quality Act, except that the owner must ensure that a fire extinguisher is in the yurt, see Utah Code Section 15A-5-104, and that the person using the yurt uses a permissible form of backcountry waste containment and disposal system. See Utah Code Section 19-5-125.

Anderson v. Provo City Corp., 2005 UT 5 - owner-occupancy conditions on supplementary accessory dwelling use are permissible.

M&S Cox Invs., LLC v. Provo City Corp., 2007 UT App 315 - Amortization of nonconforming use for ADU’s where ordinance was amended to require owner occupancy of primary dwelling.

Fuller v. Springville City, 2015 UT App 177 - property owner not entitled to nonconforming use for basement apartment because the owner could not establish that the use of the home as a multifamily dwelling was ever legally established.

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