Utah Code § 10-20-606

(1) As used in this section: (a) "Internal accessory dwelling unit" means an accessory dwelling unit created: (i) within a primary dwelling; (ii) within the footprint of the primary dwelling described in Subsection (1)(a)(i) at the time the internal accessory dwelling unit is created; and (iii) for the purpose of offering a long-term rental of 30 consecutive days or longer. (b) "Primary dwelling" means a single-family dwelling that: (i) is detached; and (ii) is occupied as the primary residence of the owner of record. (c) "Rental dwelling" means the same as that term is defined in Section 10-8-85.5. (2) A municipal ordinance may not: (a) require physical changes in a structure with a legal nonconforming rental dwelling use unless the change is for: (i) the reasonable installation of: (A) a smoke detector that is plugged in or battery operated; (B) a ground fault circuit interrupter protected outlet on existing wiring; (C) street addressing; (D) except as provided in Subsection (3), an egress bedroom window if the existing bedroom window is smaller than that required by current State Construction Code; (E) an electrical system or a plumbing system, if the existing system is not functioning or is unsafe as determined by an independent electrical or plumbing professional who is licensed in accordance with Title 58, Occupations and Professions; (F) hand or guard rails; or (G) occupancy separation doors as required by the International Residential Code; or (ii) the abatement of a structure; or (b) be enforced to terminate a legal nonconforming rental dwelling use. (3) (a) A municipality may not require physical changes to install an egress or emergency escape window in an existing bedroom that complied with the State Construction Code in effect at the time the bedroom was finished if: (i) the dwelling is an owner-occupied dwelling or a rental dwelling that is: (A) a detached one-, two-, three-, or four-family dwelling; or (B) a town home that is not more than three stories above grade with a separate means of egress; and (ii) (A) the window in the existing bedroom is smaller than that required by current State Construction Code; and (B) the change would compromise the structural integrity of the structure or could not be completed in accordance with current State Construction Code, including set-back and window well requirements. (b) Subsection (3)(a) does not apply to an internal accessory dwelling unit. (4) Nothing in this section prohibits a municipality from: (a) regulating the style of window that is required or allowed in a bedroom; (b) requiring that a window in an existing bedroom be fully openable if the openable area is less than required by current State Construction Code; or (c) requiring that an existing window not be reduced in size if the openable area is smaller than required by current State Construction Code.