Eric Jaffe, of Sidewalk Labs, recently wrote about an interesting research paper -- from the Journal of the American Planning Association -- that looked at the developer response to an inclusionary zoning policy change in London. The full research paper can be found over here.

The change was an expansion to existing mandatory IZ policies. Between 2005 and 2008, each of the 33 local authorities in Greater London reduced the minimum threshold for new housing projects. Previously it only applied to new developments with 15 or more units, but it was reduced to projects with 10 or more units. In other words, projects with a total of 10-14 units were now subject to IZ, whereas they were previously exempt.

These feel like small unit counts, but I guess it speaks to the scale of development happening in London. You generally need pretty high prices to make these kinds of boutique projects pencil out. By comparison, the IZ threshold here in Toronto is expected to be 100 or more units.

In any event, here's what happened in London:

Before the policy change developers were effectively building up to the 14 unit mark (to avoid IZ). Following that new supply dropped off. After the change, developers simply adjusted their project sizes and built more projects with less than 10 units.

Interestingly enough, the researchers found that there was generally no net loss of new homes during the study period (2004 to 2014); developers simply built more projects with lower unit counts. But more importantly, the team discovered that the policy change only kind of worked.

The increase in affordable housing was modest. The researchers uncovered a net increase of two affordable units per borough, per year, among projects within the 10-14 unit band. That's something. But London is a big place.

Of course, this is a response to a particular kind of policy change in a particular kind of market. Development is a local business and it's oftentimes hard to generalize. But it does speak to the fact that there are nuances, complexities, and market distortions to consider when it comes to land use policies.

Photo by Aaron Gilmore on Unsplash