Duplexes, triplexes, and fourplexes remain a small fraction of overall home construction despite several states' passage of reforms legalizing this type of "missing middle" housing in all residential neighborhoods.
"Multifamily development projects have been growing in size," wrote Apartment List researchers Chris Salviati and Rob Warnock in a new report parsing U.S. Census Bureau building permit data. "From 1990 to 2009, 18 percent of multifamily units permitted were in buildings with two to four units; from 2010 to 2022, this type of 'missing middle' housing accounted for just 8 percent of multifamily building permits."
