Two major housing packages are on the table in Michigan and Illinois this year that aim to curb the sprawl of single-family, detached homes in favor of denser housing development. Both include bills that would open up areas historically zoned for single-family houses to duplexes and accessory dwelling units, reduce minimum home and lot sizes, and cut parking creation requirements for new developments.
The packages pull from a menu of land use policies that climate advocates say exemplify how lawmakers can continue to advance climate goals while working to address the most politically salient issue of the day — the cost of living.
“When people are able to live in places that give them more transportation options, you have the ability to walk to do some of your chores, to take transit to work if you want. You have the option to own one car instead of two cars,” Dave Weiskopf, the senior policy director for Climate Cabinet Education, told me. “The result is that there is less pollution, and it also frees up household budgets for people to do other things with their money.”
Denser housing development doesn’t just cut down on driving. Multifamily buildings use less energy than single family homes on a per-unit basis, and are less material-intensive to build. Single-family detached homes consume upwards of 41% more energy, on average, than multifamily or attached homes. Putting more housing in areas that are already developed, often called “infill” housing, can also prevent emissions from land-use change, when undeveloped land is converted to housing. According to the Intergovernmental Panel on Climate Change’s most recent report from 2022, there is “robust evidence” that achieving more “compact and resource-efficient urban growth,” could reduce emissions by up to 26% by 2050 compared with a business-as-usual scenario.
In Illinois, Governor JB Pritzker is championing the BUILD package, short for Building Up Illinois Developments. The policies stem from a report published by a committee of real estate developers, financiers, and local government leaders that the governor convened in 2024 to look at how the state could accelerate the production of middle-income housing. Some of the recommendations were enacted last year as part of a major transportation bill to save the Chicagoland metro system. That bill prohibited cities and towns from setting minimum parking requirements for new developments near rail stations and major bus corridors, and gave the region’s transit authority permission to develop housing.
The BUILD package would expand the restrictions on parking minimums to apply statewide, not just near transit. Local governments would still be able to require that single-family homes are built with one parking spot, and that multifamily buildings have at least one spot for every two units — but those rules would represent a significant change for fast-growing cities like Naperville, which currently requires that developers build two parking spots per unit for new multifamily developments.
That may seem like a small change, but it can make a big difference for affordability. Cutting the amount of parking a developer has to provide reduces construction costs and can open up space for building additional units, enabling a higher return on investment. It also, of course, makes owning a car more of a pain, encouraging residents to find other, lower-carbon means of transportation.
The BUILD package would also legalize accessory dwelling units, or ADUs, throughout the state — another recommendation from Pritzker’s committee. ADUs are converted garages, basement units, and other small residences that are added to lots with existing homes. The movement to legalize ADUs has taken off all over the country as a small policy change that can create a lot of infill housing, and fast. California first legalized ADUs in 2016, and the number of units permitted each year has risen steadily since. By 2022, more than 80,000 ADUs had been permitted — a more than 15,000% increase.
The legislation doesn’t stop at ADUs — it would also effectively end single-family zoning. It requires municipalities to legalize multi-unit housing in all residential zones, allowing up to four units on smaller lots and eight units on larger ones. This would make it much easier to build affordable housing. Even in Chicago, about 40% of the city is currently zoned for single-family homes or duplexes.
“From my perspective, that would have the most impact if you could actually pass that,” Bob Palmer, the policy director for Housing Action Illinois, told me. “We’re not talking about larger apartment buildings or things that would significantly change the character of communities.”
Opposition to these kinds of policies tend to come from proponents of local control — those who believe cities should have the right to determine who builds what and where within their borders. “The ‘not in my backyard,’ forces in communities have outsized influence in terms of being able to oppose new housing development, and it’s created a situation where we have this really significant lack of supply and lack of adequate choices in the housing market,” said Palmer.
But constituencies for and against the types of reforms in the Illinois and Michigan housing packages do not divide neatly on party lines. Notably, Montana passed a series of laws to cut parking minimums and allow duplexes and ADUs in single-family zones in 2023 and 2025 under a Republican trifecta.
In Michigan, a broad, bipartisan coalition of lawmakers is backing a housing package that includes a nearly identical set of policies to the Illinois package, although with slightly different requirements within them. It’s garnered support from groups that rarely, if ever, sign on to the same legislation. The Michigan League of Conservation Voters and Sierra Club support the package, as does the libertarian, Koch-funded advocacy group Americans for Prosperity and the Mackinac Center for Public Policy, a nonprofit institute that supports free markets and limited government.
“It’s rare that you have a policy where Greg Gianforte and Ron DeSantis and Gavin Newsom and JB Pritzker are basically all pushing for similar legislation,” Joel Arnold, the planning and advocacy manager for Communities First, a Michigan affordable housing nonprofit, told me. “And yet that’s what we see on land use reform.”
Under DeSantis, Florida passed the Live Local Act in 2023, which required municipalities to allow large, multifamily housing on land zoned for commercial, industrial, or mixed-use development. The law did not amend areas zoned for single-family construction, but it did open up pre-developed areas to high-volume affordable housing production. A 2025 amendment to the law required local governments to lower their parking minimums for developments near transit hubs or existing parking lots.
Arnold told me that in the past, Michigan lawmakers have focused more narrowly on how to make housing more affordable. The state has steadily increased funding for and expanded its housing programs, and Governor Gretchen Whitmer set a goal last year to build or rehab 115,000 housing units by 2027. But it was becoming clear that funding wasn’t the only problem. “Our current land use and zoning structures just make the most affordable types of housing not just hard to build or annoying to build, but in most places illegal to build, like completely illegal,” Arnold said.
The proposals in Michigan and Illinois are not limited to what urbanists refer to as “transit-oriented development.” They don’t specifically encourage development near public transportation hubs — which, on an intuitive level, may seem like a missed opportunity for emissions benefits. But the kind of broad brush strategy policymakers are taking — allowing for so-called “gentle” density (i.e. smaller multifamily buildings like duplexes) everywhere, versus opening up a much smaller area to high-rises — has the potential to create a lot more housing.
“Maybe it’s not as perfect in terms of everyone’s going to be taking transit for all their trips, but there are a lot of neighborhoods that are relatively walkable to retail, schools, some jobs — where, if you’re getting in a car, you’re not driving as far,” Zack Subin, the associate research director for the Terner Center for Housing Innovation at the University of California, Berkeley, told me. “So I think increasingly that can play a role in a climate focus,” he said, later adding, “Everyone’s too over-focused on transit as the proxy for reducing driving.”
Subin’s research has shown that simply growing the housing stock in neighborhoods that have below-average car use would directly avoid about the same amount of carbon emissions as shutting down 2-3 coal-fired power plants.
If you assume that infill housing policies, such as the packages in Illinois and Michigan, can successfully grow the housing supply, he said, it’s clear that they can reduce emissions on par with other climate strategies like vehicle electrification. The big question is how quickly these policy tweaks can actually increase supply. States have only started to adopt them in the past five years or so, and development timelines can stretch on for much longer than that. “There’s a lot of suggestive evidence, but we’re kind of at the very beginning of this policy experiment,” he said.
Illinois’ General Assembly could pass Pritzker’s package as soon as next month, as the legislative session winds down at the end of May. In Michigan, the session extends through the end of the year, so the package may not come up for a vote until late fall. By year’s end, we may also see a major housing package up for a vote in Pennsylvania, where Governor Josh Shapiro recently unveiled his own Housing Action Plan, most of which would require the legislature to fund and enact.
