“Why has there been a decline in two-, three-, and fourplex units? For one thing, communities have been modifying zoning codes to eliminate this housing type, especially duplexes, in single-family residential areas. For another, because they have fewer units, these types are difficult to scale for production. So, even if they are allowed, economics works against building them. Finally, older two-, three-, and fourplex structures are often in the path of redevelopment so they may be replaced by more intensive development—perhaps high-rises comprising more than twenty units.8”