In previous centuries, residential development was mainly of two kinds. Rich people bought a townlot, hired an architect and/or contractor, and built a bespoke / customized house or mansion for their family. Poor urban people lived in shantytowns or in tenements built for rental. Single-family houses were seldom built on speculation, that is for future sale to residents not yet identified. When cities and the middle class expanded greatly and mortgage loans became commonplace, a method that had been rare became commonplace to serve the expanding demand for home ownership.