Salim Furth

Should YIMBYs support or oppose greenfield growth? Two basic values animate most YIMBYs: housing affordability and urbanism. Sprawl puts those values into tension. Let’s take as a given that sprawl is “bad” urbanism, mediocre at best. Realistically, it’s rarely going to be transit-oriented, highly walkable, or architecturally profound. So the question is whether outward, greenfield growth is necessary to achieve affordability. And the answer from urban economics is yes. You can’t get far in making a city affordable without letting it grow outward. Model 1: All hands on deck Let’s start with a nonspatial model where people demand housing space and it’s provided by both existing and new housing. Existing housing doesn’t easily disappear, so the supply curve is kinked. A citywide supply curve is the sum of a million little property-level supply curves. We can split it into two groups: infill and greenfield, which we add horizontally. If demand rises to the new purple line, you can see that the equilibrium point where both infill & greenfield are active is at a lower price & higher quantity than the infill-only line. The only way to get some infill growth to replace some greenfield growth, in this model, is to raise the overall price level. And even then, the replacement is less than 1-for-1. Of course, this is just a core YIMBY idea reversed! In most U.S. cities, greenfield growth has been allowed and infill growth sharply constrained, so that prices are higher, total growth is lower, and greenfield growth is higher than if infill were also allowed. At the most basic level, greenfield growth is simply one of the ways to meet demand. With fewer pumps working, you’ll drain less of the flood. Model 2: Paying for what you demolish Now let’s look at a spatial model where people […]