The argument behind upzoning relies, as we have said many times before, on the claim that overly restrictive zoning restrains housing production that would otherwise be economically and physically viable. One result of such a conjuncture that we would expect to see is that most parcels would be built out to their maximum entitlement. That is, parcels that could hold more than a single-family house would end up doing so. Parcels that could be subdivided would end up as multiple parcels.
Last year, we made an attempt to screen for underutilized parcels in Charlottesville. Our results can be found here. But we didn’t have good enough data to really examine the question of the full use of building or subdivision entitlement. Our mapping and data quality have improved substantially since then. We have calculated unit count, set-back and frontage information for all parcels in the city (something which, strangely, the city seems not to have done in its own database). With that information, we can find parcels that are potentially subdivisible or which hold only a SFH despite a higher entitlement. You can see a map of these parcels below, with selectable layers: underutilized (SFH on MFG) lots, subdivisible R-1 lots and subdivisible R-1S lots.
Over 1,000 parcels in Charlottesville are zoned for a more intense by-right residential use than SFH but at the same time contain only a SFH. That is larger than the number of parcels that contain multiple residential units! Moreover, our rough analysis of subdivision potential — we look for parcels that are at least 210% of the minimum lot size for the zoning category with either multiple frontages of at least 50 feet or a single frontage of over 120 feet, an average non-front setback of at least 45 feet, and a use of either SFH or vacant land — shows nearly 300 R-1 units likely to be subdivisible and another 60 R-1S parcels likely to be subdivisible. And our criteria are extremely conservative. The true number is almost certainly higher.
Once again, we see not just an absence of evidence of a zoning-mediated restriction on housing production, but evidence of an absence of such restriction. If overly restrictive zoning created a situation where, broadly, there is a strong economic incentive to build more densely that is being checked by zoning, one would at least expect to see those parcels where higher density is not checked by zoning to be exploited aggressively. We see the very opposite in Charlottesville.