Zoning Practice — August 2007

Ask the Author

Here are reader questions answered by Gerrit-Jan Knaap and Megan Rhodes,co-authors of the July 2007 Zoning Practice article "Is Zoning a Barrier to Multifamily Housing?"

Question from Peter Noonan, Associate Planner, City of Beverly Hills, California:

Cities in the Southern California region are facing difficultly providing adequate housing for our growing populations, let alone housing that is affordable to low and middle income households. In order to own a home, much of the region's work force commutes long distances to and from work. Many cities have undertaken studies to identify policy and program options that would encourage the development of housing that is affordable to working-class Californians. One aspect being tested is establishing maximum unit sizes as a regulatory means of reducing average housing cost. I am curious if this has been effective in other regions and if there is an optimal ratio of units per acre in built out areas. I imagine if there was a ratio that it would be complex given local variation in the cost of land, entitlement and construction, etc. I ask because my city currently has a minimum unit size that I suspect is limiting opportunities for more affordable housing. Any thoughts would be greatly appreciated!

Answer from author Gerrit Knaap:

Your question is a good one and addresses precisely the problem we describe in our article. The housing affordability problem in California communities is not unusual, however. We are not very familiar with ordinances that specify maximum house size, though there are examples here in the Washington, D.C., area. In most cases, these kinds of ordinances are primarily concerned with aesthetics, however, making sure that large new houses are not grossly out of proportion with the existing housing stock. We were not aware that such ordinances were used to promote housing affordability, and we don't think they could help much in that regard. On the other hand, minimum unit size restrictions certainly don't help either.

As for the optimal ratio of units per acre, this is something that economists can derive in deterministic models of urban form. Specifically, according to urban economic theory, there is an optimal housing unit density for any given set of land and housing prices. In the real word, however, it's much more difficult. Our sense is that the "optimal" ratio does not really exist, and that residential densities, as other critical features of the urban landscape, can best be determined by a comprehensive planning process that includes careful analysis and widespread public participation.