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To fix its housing crisis, California must unleash the duplex

By Emily Hamilton, Bloomberg CityLab, March 1, 2022

“California’s Senate Bill 9 … circumvents local zoning rules by allowing owners of single-family homes to split their properties into two lots and build two units on each. The first SB9 project will include four new homes on a one-acre, formerly one-house lot in Palo Alto.

“But … SB9 will have far more impact if local leaders cooperate with the spirit of the law by relaxing some of the rules that … make duplexes less attractive to build.

“Under SB9, localities are only required to permit units up to 800 square feet … but the average detached house sold in 2020 was 2,333 square feet. … California needs … local leaders to go further…: Legalizing larger units would lead to more of them being financially feasible.

“[L]ook to Palisades Park, a small town in New Jersey with an approach to zoning for duplexes that works for homebuilders and homebuyers. 

“The town’s comparatively open zoning codes allow … three-story, side-by-side duplexes with small setbacks; they are typically spacious and well-appointed, with each of the two units often larger than the single-family house they replaced. … [The] new … units are less expensive than new construction in neighboring localities in part because two households can share the cost of one lot. 

“[T]he success of duplexes in Palisades Park hinges on the size and desirability of its new housing. If their duplex units were limited to 800 square feet, redevelopment wouldn’t make financial sense. … For SB9 to succeed in substantially expanding California’s housing supply, its cities will … need to increase the square footage of living space permitted on their lots.”

Emily Hamilton is the director of the Urbanity project at the Mercatus Center at George Mason University and coauthor of the new study“Light Touch Density.”

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