Triangular plots from old railroad lines. Crescent-shaped parcels that used to be parking lots. And narrow strips of land squeezed between buildings.

For decades, builders ignored irregular lots, typically smaller and narrower than the standard square ones, because of zoning codes and rules. But as usable land becomes increasingly limited in urban areas, more cities and states are moving to change regulations to allow for building on odd plots, and for additional housing on land traditionally reserved for single-family homes.

Over the past year alone, the nation’s 250 largest cities have made 257 significant zoning changes to clear the path for denser development, according to an analysis provided by ReZone AI, a firm that analyzes municipal zoning.

State-level zoning changes have also accelerated, said Alex Horowitz, director of the housing policy initiative at the Pew Charitable Trusts. From 2023 to 2024, 96 laws were passed to help increase housing production, including adding more development in a given area, and 80 laws have been passed this year.

The zoning changes get rid of minimum lot sizes and parking requirements that housing advocates and developers say have made it nearly impossible to build “the missing middle,” or a variety of housing styles that fall between single-family homes and larger apartment buildings.