Measuring Informal Housing Production in California Cities

Problem, research strategy, and ­findings: Planning scholars and practitioners once assumed informal housing was largely absent in the developed world; today they increasingly acknowledge its role in the United States. Recent evidence suggests that informal housing, or non-permitted construction, is a significant phenomenon inside incorporated cities, despite widespread regulations and code enforcement. Informal housing is a de facto source of otherwise scarce affordable housing in many locations, but also compromises health and safety and strains municipal infrastructure and fiscal health. Planners lack a means of measuring informal construction at the scale of individual cities. We propose such a method, and apply it to incorporated cities in California. Data limitations prevent us from precisely estimating the magnitude of non-permitted construction, but our findings suggest that informal channels are an important source of housing production, especially in the places where permitted construction is constrained.Takeaway for practice: We urge planners to engage with informal housing issues, given the considerable importance of this hidden yet vital portion of the housing market as a means of providing living spaces amid tight housing market conditions. Our method for calculating the rate of informal housing addition is a useful tool for planners to gather basic facts about the informal housing market in their communities, a prerequisite for policy interventions.