Zoning for Accessory Housing

Zoning Practice — July 2012

By Thomas Daniels


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Accessory housing may either be a detached dwelling unit with full services — bath, sleeping quarters, and kitchen — or an autonomous apartment attached to a house. Whether attached or detached, accessory housing can increase residential densities and encourage walkability. However, many older zoning ordinances present major obstacles to the creation of accessory dwelling units (ADUs).

Efforts to retrofit suburbs and encourage infill in cities have often focused on large projects such as redeveloping dead malls and multistory mixed use commercial and residential buildings. But financing for these projects is less available since the 2007 downturn in the real estate market. One less conspicuous way to provide more rental units is through an accessory housing ordinance in single-family residential districts.

This issue of Zoning Practice outlines a strategy for incorporating accessory housing standards into local zoning codes and highlights a few examples of communities where this approach has been effective.


Page Count
Date Published
July 1, 2012
Adobe PDF
American Planning Association

About the Author

Thomas Daniels
Professor Tom Daniels teaches Land Use Planning and Growth Management at the University of Pennsylvania. He is the author of When City and Country Collide: Managing Growth in the Metropolitan Fringe (Island Press 1998) and "The Napa County Agricultural Preserve: 50 years as the Foundation of America's Premier Wine Industry" Journal of Planning History, forthcoming in 2019. Tom has written extensively on growth management and he recognizes that affordable housing is one of the great challenges of a successful growth management system. Tom has given several presentations at the American Planning Association Conference.