Accessory Dwelling Units (ADUs)

ADU types

How to Apply

Before applying, please review the ADU FAQs below.

To apply for an ADU, please complete the following documents and provide all other necessary documentation required by Planning & Zoning. Any new detached ADU must apply for a site plan review application with Planning & Zoning to receive approval. An ADU application must be completed with the Planning & Zoning department before a building permit can be applied for.

Please upload the completed documents through the planning application portal linked HERE.

The Planning & Zoning Department will review the application and will contact the applicant regarding next steps. An ADU may require a building permit, and anyone who wishes to rent an ADU must also obtain a Millcreek business license.

The City Council adopted an Accessory Dwelling Unit (ADU) ordinance on September 27, 2021 that became effective November 15, 2021. Since this adoption, changes have been made to the Millcreek ADU ordinance. The ADU ordinance in the Millcreek code is the best place to get up to date and accurate info about ADUs in Millcreek. The Millcreek ADU ordinance can be found HERE.

ADU FAQs

What is an ADU?

An Accessory Dwelling Unit, or ADU, is a secondary living unit on a property that already has a single household. ADUs can take multiple forms and can allow for multi generational living on a single property. Property owners who have an ADU can also rent them out so long as they live on the property year round and get all the necessary approvals from Planning & Zoning and the Business Licensing Department. The State of Utah requires that all municipalities allow for internal ADUs and encourages municipalities to allow for other forms of ADUs as well. You can read the State law regarding internal ADUs HERE.

The three type of allowable ADUs in Millcreek are listed below.

Internal – an internal ADU is a residence located within the existing footprint of a home. Traditionally, these ADUs have been called mother-in-law apartments.

Attached – an attached ADU is a residence constructed as an addition to an existing home.

Detached – a detached ADU is a residence in a separate structure on the same lot as the existing home. A detached ADU can be a new building, or an existing building could be converted into an ADU in certain circumstances.

Why are we allowing ADUs?

Millcreek's General Plan calls on us to “strive for a variety of housing choices in types, styles, and costs of housing throughout Millcreek.” As it is becoming increasingly expensive to live in Millcreek, ADUs can help add more small scale housing, allow for residents to make extra income off ADU rentals, and add housing in areas of Millcreek that are largely built out. ADUs are a part of a multi-pronged strategy to promote more opportunities for affordable housing in Millcreek.

Where are ADUs allowed? How big can they be?

ADUs are allowed only in a R-1 (single-family residential) or A (agriculture) zones. In addition, the following requirements apply:

Lot Size – A detached ADU requires a lot that is at least 8,000 square feet in area. Internal and attached ADUs do not have lot size minimums, but must adhere to all the underlying zoning rules (lot coverage, parking, etc.).

Location – A detached ADU must be in a rear yard. An exterior door to an internal or attached ADU must be on the side or rear of the residence.

ADU Size – A detached ADU can be up to 1,000 square feet. The size of an ADU can be limited by the total lot coverage allowance in any specific zone.

ADU Occupancy – Attached and detached ADUs can house no more than two adults, and any number of children.

How close can an ADU be to my house?

Attached ADUs are subject to the side and rear yard requirements of any single-family home. A new detached ADU must be at least 5 feet from the side or rear property line of the property it’s on. An ADU conversion of an existing detached structure is possible, provided that the setbacks of the existing structure do not change, and the structure meets all building and fire codes.

How tall can a detached ADU be?

A detached ADU may be as tall as any detached accessory structure. In most cases, the maximum height of an ADU is 24 feet. Structures with a height greater than 14 feet must be further set back than the minimum requirement of 5 feet. If someone converts an existing nonconforming structure into an ADU, they cannot increase the height of the existing structure.

What are the design standards? Where can windows and doors be located?

When located within 15 feet of a neighboring property, all windows facing the neighboring property must be frosted and fixed. Second story balconies on detached ADUs are prohibited. In addition, ADUs are prohibited on slopes greater than 30%. ADUs are also subject to the building envelope and lot coverage requirements found in the base zone of the property that the ADU is located on. 

Where will everyone park?

All ADUs are required to have at least one off-street parking stall, and no ADU parking is allowed on the street. If someone wishes to convert their garage into an ADU, that is only possible if the lot can accommodate at least one additional parking space for the ADU, and they must replace their garage parking with at least one covered stall.

What about utilities?

Because ADUs are accessory to the main single-family homes, ADUs are not allowed to have separate utility meters. All utilities must be serviced from the main single-family home. Secondary meters may be allowed to monitor utility usage on an ADU. Residents are encouraged to work with their utility providers if they wish to have secondary meters installed.

Do I have to live in the home I own in order to have an ADU on my property?

Yes. ADUs are only eligible on lots that have owner-occupied dwellings. Upon approval, the city will record a notice on the property title stating that the eligibility for an ADU is contingent upon owner occupancy.

Can I use an ADU as a short-term rental?

Short-term rentals in detached ADUs are prohibited. Internal and attached ADUs may operate short term rentals. To do this, a property owner must file and ADU application with Millcreek and obtain a Millcreek business license for the rental. Long term rentals (30+ days) are allowed in all ADUs so long as the property owner has received an ADU compliance letter from Millcreek and obtained a business license.

What are the permit and license requirements?

Some ADUs will require a building permit. As part of a building permit, a city engineer, a planner, and the Fire Marshal will review the project for compliance with all applicable building, fire, zoning, and engineering requirements.  Anyone who wishes to rent an ADU must also obtain a Millcreek business license. If an existing building doesn’t comply with current setback, height, or coverage requirements, an attached ADU or an ADU conversion may require a permit from the Land Use Hearing Officer.

Where can I read the rules?

Click HERE for a copy of the adopted ADU ordinance.