Planning commission backs council changes to detached ADU rules, cites state septic code

The Mayfield Town Planning Commission voted March 31 to recommend council-approved changes to the town’s detached accessory dwelling unit (DADU) rules, including explicit reference to state septic standards and limits on DADU size and height.

Staff member (S2) told the commission the council had separated internal ADUs (IADUs) from detached ADUs and proposed adding a reference to the state septic-design standard. As S2 put it, “We can still permit them, but we have to allow them,” describing the state’s direction that internal ADUs cannot be prohibited.

Commission members and staff reviewed proposed eligibility and dimensional limits: a suggested minimum lot size of 30,000 square feet for detached units in much of town (based on local soils typically rated class 4–5), a size range of roughly 500–1,000 square feet for DADUs, and a height limit not to exceed the primary dwelling or 25 feet. The commission discussed septic-system constraints, including whether the health department would allow a single larger tank and replacement drain-field allocation for multiple dwellings, and whether the town should limit bedrooms in accessory units pending sewer improvements.

Commission member (S1) summarized the definition debated by the group: “Accessory dwelling [is] a single self-contained residential unit providing complete independent living facilities for one or more persons including the sleeping, eating, cooking, sanitation.” Commissioners also discussed tying occupancy permits to lot consolidation and impact-fee payment and noted HOA rules that could restrict development regardless of municipal approvals.

A motion to recommend the council’s DADU changes, including adding Utah Administrative Code R317-4-13 for septic design criteria, passed. Staff announced the changes are scheduled for a public hearing next Wednesday at 7 p.m.