In the last few years, an increasing number of states has ended single-family zoning, either partially or totally. The statutes either allow two separate units or accessory dwelling units that convert parts of a single-family home into a duplex. These states include Oregon (2019), California (2021), Maine (2022), Washington (2023), and Montana (2023).
The statutes can be found here:
Cal. Gov’t Code §§65852.21, 66411.7, 66452.6 (Housing Opportunity and More Efficiency Act (HOME Act) (SB 9, eff. Jan. 1, 2022))
Me. Rev. Stat. §4364, 4364-A, 4364-B (L.D. 2003, 2022 Leg., 130th Sess. (Me. 2022))
Mont Code §§ 76-2-304, 76-2-309 76-2-345 (S.B. 245, Mont. Laws 2023, ch. 499 §1, eff. Jan. 1, 2024)
Or. Rev. Stat. §197A.420 (H.B. 2001, Aug. 8, 2019)
Or. Rev. Stat. §215.495 (H.B. 1337, June 23, 2021)
Wash. Rev. Code. §36.70A.030, §36.70A.635 (H.B. 1110 (Apr. 11, 2023); S.H.B. 2321 (June 6, 2024))
These laws change zoning but do not affect covenants that limit property to single-family structures. These legislatures appear to have worried that invalidating covenants might violate the Takings Clause. I think they are wrong about that but they are not wrong to worry about it.
There are challenges to these laws in state courts and two courts have held these laws to be unconstitutional for various reasons. The California statute was held to have violated the state constitution by interfering with the power of home rule municipalities to make their own laws. State law allows such overrides for matters of statewide concern but one judge thought that the law was not sufficiently crafted to achieve its ends and thus violated the California Constitution. See City of Redondo Beach v. Bonta, 2024 WL 1860434 (Cal. Super. Ct. 2024).
The Montana law has been put on hold by a judge who thinks it violates the equal protection clause because it treats those who have restrictive covenants differently from those who do not. Montanans Against Irresponsible Densification, LLC v. State of Montana (Dec. 29, 2023). The same opinion suggests that it would be unconstitutional to override restrictive covenants so that might be a rational reason to treat the two types of owners differently.
These lower courts opinions may well get overturned but they show continued opposition to laws that are intended to help the affordable housing crisis by deregulating land to allow greater density.