The State of California seeks to increase housing production by regulating the number of homes local zoning allows, yet the market feasibility of delivering units under more expansive zoning is rarely acknowledged and mostly unanalyzed. New guidelines from the Department of Housing and Community Development emphasize the need to assess realistic capacity of sites, including the feasibility of new housing development during the upcoming planning period. One statewide policy push is to allow three- and fourplexes in single-family zones. To assess the impact of this zoning change, we analyze the market feasibility of homebuilding under fourplex zoning on the 6.8 million parcels with single-family homes built in California prior to 2005.