A bipartisan bill just introduced in the Montana Senate would prohibit cities and counties from adopting regulations that stand in the way of building new accessory dwelling units — small cottages or apartments that share properties with larger single-family homes.

Senate Bill 397 was introduced by Sens. Greg Hertz of Polson and Ellie Boldman of Missoula, who say it aims to create more affordable housing in the state's burgeoning urban centers by prohibiting zoning rules that make it onerous or impossible to build accessory dwellings.

If the bill becomes law, local governments could not require anything more than standard building permits when homeowners seek to add secondary dwellings on their land.

"SB 397 is designed to let property owners have more control over their own property and create more housing," said Hertz, a Republican.

"This bill will end discriminatory government rules and give Montanans more options to secure a safe and affordable place to live," said Boldman, a Democrat.

The legislation would have no effect on private covenants, meaning homeowners associations still could prohibit or make rules about accessory dwellings.

The bill was scheduled to receive its first hearing Monday afternoon in the Senate Local Government Committee.

It promises to be controversial among city leaders who view it as another attempt to strip them of local control and apply a one-size-fits-all solution to the complex problem of housing affordability.

Whitefish City Council member Ben Davis said accessory dwellings already are allowed in most of the city, and the Strategic Housing Plan Steering Committee, which he chairs, is looking at ways those units can help solve the affordability problem. But, he said in an email, SB 397 doesn't account for nuances in Whitefish's specific housing needs.

"There are collateral impacts that are not being considered, such as impacts on existing neighborhoods and the fact that many of these are built for use as second homes, which does not actually help the local housing issue here in Whitefish, and may in fact exacerbate difficulties for local residents in purchasing single-family homes," said Davis, who is also a home builder.

Some accessory dwellings in Whitefish, Davis noted, are built as investment properties, with the primary and secondary residences being rented out to different tenants. That removes homes from the market for local workers looking to buy, and makes the whole property more expensive in the future.

"These are trade-offs, and good policy I believe will seek to strike a balance that is actually working towards the overall needs of the community," Davis said.

"Housing and zoning issues are complicated, and the needs and challenges vary considerably depending on the city, especially so for Whitefish, and I strongly believe that these decisions must always be made at the local level," he said. "The state Legislature simply does not, and indeed cannot, study the issue and impacts sufficiently to make good policy in this area."

In Kalispell, where accessory dwellings are prohibited in some residential zones, the City Council recently debated a proposed ordinance that would have expanded the areas where they are permissible. The council unexpectedly scrapped the plan last month but is expected to take it back up for consideration.

Kalispell City Manager Doug Russell said SB 397 would preclude local leaders from even having that discussion.

"They're trying to preempt local authority from really enacting any type of policy within a respective, individual community," he said.

Hertz said cities including Billings, Bozeman and Missoula have imposed too stringent rules on accessory dwellings, such as 600-square-foot size limitations and mandatory additional parking, adding significant expense to otherwise modest building projects.

"It really made it difficult to do these things," he said. "And they're taking away people's private property rights, too."

Mayre Flowers, a Kalispell-based planning consultant who regularly testifies on housing legislation, echoed those concerns. As Montana's housing market experiences a "feeding frenzy" of buyers from out of state, she said, local governments should be allowed to impose reasonable restrictions on accessory dwellings, since many are used as short-term rentals such as Airbnbs.

"When they add a secondary dwelling, it is often allowing that homeowner, who is in the local workforce, to be able to live more affordably as well," Flowers said. "But when both housing units become simply an investment property, we're losing a significant amount of existing workforce housing."

Hertz said his bill would not preclude cities from using zoning restrictions to limit numbers of short-term rentals, nor would it interfere with standard building rules such as setback requirements.

"I think a lot of people have unrealistic concerns it's going to turn a bunch of single-family homes into duplexes," he said.