Counties eyed for ADU expansion as sanitarians warn 15-day DEQ review may be too short

Senator Forrest Mandeville described Senate Bill 532 to the Senate Local Government Committee as a county-level extension of the ADU (accessory dwelling unit) law the Legislature enacted for municipalities last session. "This is the county ADU bill as we have been referring to it," the sponsor said, explaining the measure largely mirrors the municipal language but allows counties to require an expedited sanitation review by the Department of Environmental Quality (DEQ) with a proposed four-year sunset on that expedited DEQ process.

Supporters including Jake Brown (Shelter Whitefish), AARP Montana (Tim Summers), the Frontier Institute and building-industry representatives said ADUs are an established, low-cost housing option that helps aging Montanans, multigenerational households and homeowners seeking rental income. Samuel Hooper (Institute for Justice) framed the bill as a property-rights extension to county lines.

Opponents — chiefly county sanitarians and public-health officials — raised technical and public-safety objections. Charles Shane (Montana Environmental Health Association) and Beth Norberg (Lewis & Clark Public Health) warned that the bill’s 15-calendar-day expedited review for DEQ-sanctioned sanitation actions more than halves the typical review timeframe (commonly 30–45 days) and would strain limited sanitarian staffing. They said rushed reviews risk errors affecting sewage treatment, drinking-water safety and stormwater management.

DEQ’s subdivision section supervisor, Sean Rowland, clarified DEQ practice: a full ADU (with full kitchen and laundry) is treated as a separate dwelling unit under the Montana Water Quality Act for wastewater and mixing-zone calculations. Rowland said an ADU typically requires separate wastewater review and that automatic classification as an ADU — versus merely an added bedroom — affects review requirements.

Members asked whether the 15-day timeline only applies when an existing wastewater system demonstrably has capacity. Senator Mandeville said the expedited review was designed for cases where capacity exists and that he had discussed a sunset on DEQ items to limit unintended burdens. Sanitarians recommended 30 days as a more feasible minimum for thorough review.

The sponsor told the committee he is willing to work on amendments to definitions and timelines following the hearing. The committee closed the hearing without voting on the bill and moved to executive action on other items.

Ending

Senator Mandeville asked for a due pass and signaled willingness to consider amendments, particularly around sanitation review timing and clarifying ADU definitions so local health reviewers and DEQ can preserve public-health protections while reducing regulatory barriers to ADUs.