Mayfield council narrows proposed detached-ADU rules, sets 30,000-sq-ft minimum

Council member (S3) told fellow Mayfield Town Council members on March 4 that state and county on-site wastewater guidance makes detached accessory dwelling units (ADUs) difficult to place on small lots.

"So in order to have an ADU with an additional septic system, you'd have to have at least 30,000 square feet," Council member (S3) said, summarizing a county soils table and a conversation with the county environmental health scientist.

Why it matters: The council is deciding whether and how to allow detached ADUs in Mayfield, and the final rules will determine how many property owners can build rental units, where new septic systems may be sited and what fees they must pay.

What the council decided and why: After reviewing draft ordinance language and state/county guidance, council members agreed to a numeric minimum for detached ADUs (30,000 square feet), to explicitly require a separate septic system for detached units, and to reference Central Utah Health Department rules rather than trying to re‑state complex soil-chart logic inside the ordinance. "We'll let the percolation test decide the soil type," Chair (S2) said during the debate, and the council agreed to rely on the health department to determine system feasibility.

On accessory buildings: Council members rejected allowing ADUs inside existing accessory structures such as pole barns or metal buildings, citing code, foundation and fire‑egress concerns. "If somebody has a pole barn, it's not gonna have a proper foundation for actual building," S3 said while arguing to remove an allowance for accessory‑building ADUs.

Impact fees and utilities: Council reviewed the town’s fee breakdown and the likely costs to someone building a detached ADU. Staff read an impact-fee total of about $10,142.52, broken into a road fee ($1,739.43), parks/open-space fee ($3,281.25) and water impact fee ($5,121.84). Council members noted that water-connection and meter costs are charged separately by utilities and that the ordinance will reference the town fee schedule so future fee changes do not force ordinance amendments.

Next steps: The council asked staff to update the draft (reflecting the agreed 30,000-square-foot minimum, the separate-septic requirement for detached units, and the accessory-building prohibition), to reference the Central Utah Health Department percolation rules, and to prepare a 10‑day public-notice packet for an April public hearing. Planning commission feedback will be incorporated before the hearing.

What remains unresolved: Members discussed grandfathered lots with existing septic systems and whether those properties could qualify; they also did not complete final language on meter waivers or discounted impact-fee options, noting any fee changes would require a separate formal process.

The council adjourned the ADU discussion with an instruction to circulate an updated draft and to schedule the public hearing in April.