ADU rules in Mapleton

An accessory apartment may be permitted in a detached building only on lots of at least 21,780 sq ft (half acre); the detached structure's front wall must be at least 10 ft behind the front wall of the primary dwelling. Unlike the internal-unit subsection, the detached subsection does not list eligible zones.

Internal accessory apartments (as defined in Utah Code 10-9a-511.5) are allowed in all residential zones except the SDP-1 and R-2-B zones, on a legal lot of record of at least 6,000 sq ft; the unit must not change the building's single-family appearance and its entrance must be on the side or rear. The code regulates only internal and detached types; an accessory apartment is defined as a subordinate portion of a single-family dwelling (§18.08.010).

Detached apartment interior floor area may not exceed 40% of the primary dwelling's square footage or, whichever is less: 1,000 sq ft on lots of 21,780 to 87,119 sq ft; 1,200 sq ft on lots of 87,120 to 130,679 sq ft; 1,400 sq ft on lots of 3 acres or more. The internal-unit subsection (D) sets no size cap.

Either the primary dwelling or the accessory apartment must be occupied by a full-time resident property owner as shown on the Utah County tax assessment rolls. The section is titled Owner Occupied Accessory Apartments; its provisions do not apply if only family members (as defined in §18.08.010) reside at the residence.

The designated stall must be paved (asphalt, concrete, or dust-free hard surface); it may not be in a garage unless at least 2 other garage stalls remain for the primary unit, may not sit directly behind a required primary-dwelling stall, and no more than one designated stall may be in the front yard setback or a street-side yard setback.

Before construction or occupancy the owner submits an accessory apartment permit application to the Community Development Department and pays an administrative fee; no public hearing or conditional use process is specified. Each kitchen also requires a building permit under §18.84.415, which exists to enforce §18.84.410. Accessory apartments do not appear in any zone's permitted or conditional use lists; they are regulated entirely through this supplementary section.

§18.84.425 prohibits short-term rentals (stays under 30 consecutive days) in all zones. §18.84.410(C) limits each lot to one accessory apartment. No minimum lease term or other long-term rental restriction was found in the ADU section.