Accessory Dwelling Units (ADUs) – A Best Practice Guide

Accessory Dwelling Units (ADUs) 

A Best Practice Guide

Last Updated-2020.04.02

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Issue Overview 

Accessory Dwelling Units (ADUs) are becoming a popular choice among Utah’s communities, who are trying to meet the requirements of the state’s new affordable housing mandate, in an attempt to address the statewide shortage of moderately priced homes. In addition to providing a simple way of creating more affordable housing, ADUs also allow those who want them, a creative way to take care of aging relatives, or a way to simply supplement their mortgage / income by renting out the ADU. 

While ADUs provide a solution to the affordable housing shortage, they also can inadvertently create problems within communities if they are not planned for properly. The problems which typically arise with ADUs are those commonly associated with higher density (i.e. encroachment, noise, parking,  and traffic), as the community is almost always doubling the amount of allowed dwelling units within the existing zoning district when they allow for ADU development.

Things to Consider 

  • With the population along the Wasatch Front anticipated to increase by approximately 1.5 million people by 2050, the Utah State Legislature has expressly highlighted ADU development as a potential solution to the ongoing affordable housing crisis / issue.  
  • Communities looking to adopt ordinances pertaining to ADUs should ensure those ordinances contain unique requirements which are designed to mitigate the potential negative impacts to adjacent property owners, including the surrounding community as a whole. 
  • While this course is geared primarily towards the discussion surrounding detached ADU’s (i.e. an additional dwelling unit that is detached from and secondary to the main dwelling unit), it should also be noted that ADU’s can be internal (i.e. attached to, or part of the existing dwelling unit).  
  • In some instances it may be appropriate for ADUs to be included in all zoning districts.  In some instances, it may not.  Communities should not be afraid to exclude or restrict ADU development within specific zoning districts or areas due to critical issues such as lack of lot size, utilities, or  infrastructure.   

Best Practice Recommendations

  • When crafting your local ordinance, it should be noted that ADUs can either be allowed as a permitted use (use by right), or as a conditional use (allowed only by the approval of a  conditional use permit) within a specific zoning district.  Regardless of if the use is deemed permitted or conditional, the ordinance should specify exactly how the ADU is to be developed (i.e. location, access, setbacks, separation from existing structures, size, building aesthetics, required parking, etc.)  This helps to ensure each ADU is reviewed and developed consistently pursuant to the community’s vision
  • As previously stated, not every neighborhood can accommodate detached ADUs.  Carefully review the requirements of your existing zoning districts (i.e. minimum lot size, setbacks, etc.) to determine which zoning districts allow for the best possible locations for ADU development.  If a zoning district is not sufficient in size to accommodate a detached ADU, consider the alternatives.  Could an internal ADU be an appropriate solution if additional on-site parking can be accommodated?
  • Consider requiring additional / necessary parking spaces for the ADU off-street. Requiring on-site parking spaces for the ADU not only helps to minimize the potential for nuisance complaints from neighboring properties and the surrounding community as a whole, but it also helps to ensure that cul-de-sacs and narrow streets remain free and clear for fire apparatus and other critical emergency response vehicles.   
  • Remember that public safety and emergency services need ADUs to have easily recognizable and identifiable address numbers so that they can target their responses better. Consider implementing a standardized addressing system for ADUs in order to ensure timely responses of public safety and emergency personnel if your community does not have one.
  • Implement business license requirements if the ADU is to be rented.  An ADU is more useful to a homeowner if its occupancy is not restricted / limited to family members or temporary, non-paying guests.  Keep in mind that ordinance requirements that restrict items such as the latter are extremely hard to determine for compliance / enforcement when a nuisance complaint is filed with the community.  This in turn frequently leads to disgruntled neighbors, frustrated staff members, and only adds to the argument of the existence of  too many onerous code requirements.    
  • Lastly, ADUs are considered a more sustainable option if there are separate water and sewer hookups.

Related Issues 

Zoning;  Subdivisions;  Business Licenses;  Nuisances