The missing middle : understanding low-rise, moderate-density housing in Greater Boston

Abstract

Over the past 75 years, the United States' housing stock has become increasingly bifurcated, with the overwhelming majority of units taking the form of single-family homes or mid- and high-rise apartments and condos. This trend has made scarce the kinds of low-rise, moderate-density typologies that had historically provided the dense, compact urbanism necessary to support transit, walkability, and neighborhood retail. Dubbed the "Missing Middle" by their advocates, these housing types - townhouses, duplexes, courtyard apartments, and the like - are championed for their potential to deliver the benefits of residential density in forms that are more compatible with the character of existing suburban neighborhoods than their larger multifamily counterparts. They are also promoted for their ability to improve affordability in hot housing markets through the incremental addition of smaller units and improved land use efficiency. This thesis seeks to explore the concept of the Missing Middle including the characteristics of its forms, the trends in its permitting and construction, and the barriers to its development. Focusing on Greater Boston, and three of its suburban towns in particular, the research draws on census data analysis and semi-structured interviews to understand the distribution of this housing in the region, the extent to which its development lives up to the claims of advocates, and the potential reasons for its decline. Results indicate that while Missing Middle units have historically been concentrated in cities in Greater Boston's urban core, some suburbs are experiencing an increased interest in their development. However, in many cases, recently constructed examples of the Missing Middle in suburban contexts do not achieve the walkability and affordability goals of its supporters. The research finds that barriers to the permitting of suburban Missing Middle units are largely regulatory in nature, stemming from density restrictions driven by fiscal zoning considerations and homeowners' opposition to growth, especially in wealthier communities. These findings point to the need for strong regional planning to work across town boundaries, loosening restrictive local zoning while developing adequate protections for neighborhood character in order to promote Missing Middle housing in the development of smart growth and affordability plans and policies.