Alpine homeowners on lots of at least 11,000 square feet could soon build a detached backyard dwelling unit under proposed code language the Planning Commission will review at its Tuesday, Aug. 4, meeting at 6 p.m. at City Hall, 20 North Main St.

The rules implement Utah's Senate Bill 284, which requires every city with a population of 5,000 or more to allow detached accessory dwelling units by Oct. 1. Alpine, with an estimated population of 10,444, already permits interior ADUs — basement apartments and in-home suites — under an ordinance adopted in October 2023. The new code would add freestanding backyard structures as a separate permitted category.

As we reported July 23, the meeting was announced without code specifics. The agenda packet published July 30 now spells out what Alpine can and cannot require.

What the proposed code allows

Under state law, Alpine cannot require a conditional use permit for a detached ADU in a residential zone. But the city can impose several conditions:

  • Owner-occupancy: The property owner must live in either the main home or the ADU.
  • No short-term rentals: Units cannot be rented for fewer than 90 consecutive days.
  • Parking: No more than two on-site spaces for units 650 square feet or larger; one space for smaller units.
  • Design: The ADU must match the main home's design and cannot be larger than the primary dwelling.
  • Location: No ADUs in front yards, public utility easements, or recorded easements.
  • One per lot: Only one ADU, internal or detached, is allowed per property.
  • Setbacks: The city may regulate proximity to property lines, window orientation, and massing.

If a homeowner converts a detached garage, any displaced parking spaces must be replaced on-site. The city can also deny a permit if sewer, water, or stormwater systems lack capacity.

Capacity concerns raised earlier

Infrastructure capacity has been a concern since the bill was pending in the legislature. At a Jan. 27 City Council work session, City Administrator Shane Sorensen asked what impact detached ADUs would have on Alpine's water and sewer master plans.

"I am concerned about detached ADUs because it will increase capacity, and we have large lots in Alpine that could accommodate detached ADUs," Mayor Carla Merrill said at that January meeting. "It would be expensive to increase capacity for both the water and sewer systems."

Engineer John Schiess of Horrocks Engineers told the council that a few new ADUs probably would not strain the system, but if many are added, sewer and culinary water capacity would need to be reevaluated.

What happens next

Tuesday's review is a discussion item only. No vote will be taken. Planning Commission Chair Alan MacDonald will lead the session, and the code will return to the commission for a formal recommendation at a future meeting before going to City Council for adoption ahead of the Oct. 1 state deadline.

The 11,000-square-foot threshold is the state-mandated minimum lot size Alpine must allow, though the city could choose to permit ADUs on smaller lots as well.

Residents can attend in person or watch via the Alpine City YouTube Channel, linked from alpineut.gov.