On Redeveloping Single Family

Many years ago, I worked on analyzing when real estate would redevelop, and the analysis simply ignored single family homes, because they rarely redevelop. As long as you have land to spare, you can simply add more building. And in many cases, adding another story is also trivial. So it's not until you run up against fire code for wooden structures (at five stories) and 100% lot coverage that demolition and replacement is a better alternative to a structural retrofit.  And that's a greater level of density than 99% of America.

Of course, doing that is illegal almost everywhere. Partially for good reasons (fire code). But you can see the dynamic in action in wealth neighborhoods--where people aren't running afoul of unit limits, parking requirements, or non-related family status laws. People just keep adding on extensions, with some minimal setback from the neighbor's house. Generates terrible internal floorplans over time, so eventually someone guts everything inside the walls, improves the foundation, and builds something of similar dimensions but much better quality. Without various zoning laws, the same dynamic would apply to multifamily, but we can't have Those People in Our Nice Owner-Occupied Single-Family Neighborhood.