Missing Middle Housing

Missing middle housing refers to house-scale buildings that contain multiple homes — duplexes, triplexes, fourplexes, courtyard apartments, townhouses, and similar forms — that sit between detached single-family houses and mid-rise apartment buildings. The term is "missing" because much of this housing type became difficult or illegal to build under twentieth-century zoning that separated single-family neighborhoods from larger multifamily development, leaving a gap in the middle of the spectrum.

These building types share a key trait: they fit the scale and rhythm of a traditional residential street while quietly housing more families per lot. A fourplex can look much like a large house from the sidewalk, and a row of townhouses reads as a single block face. That makes missing middle housing attractive to planners and policymakers trying to add homes gently in existing neighborhoods without the visual disruption or infrastructure load of large apartment blocks.

Missing middle housing is closely tied to recent zoning reforms. Tools that allow more units on residential lots — including California's SB-9 and SB-10, and the spread of by-right or ministerial approval for small multi-unit projects — are largely about re-legalizing these forms. ADUs are sometimes grouped into the broader missing-middle conversation as well, since they add a unit at a house-compatible scale.

What is permitted, and how easily, depends heavily on local zoning and any state laws a city has adopted, and these rules continue to evolve. This is a general overview of a planning concept, not a description of what is allowed on any specific parcel — verify local zoning with the jurisdiction.