In cities and towns across the country, hundreds of acres of urban land are going to waste. In the Bay Area, it has reached the status of blight. Along Main Streets and within retail clusters across the country, it lies dead, draining life from the streets that host it. No, I’m not talking about parking requirements. I’m talking about ground-floor retail.

If you live in an urban neighborhood, you probably already know what I’m talking about: the rows of empty storefronts and stray mixed-use buildings that can never stay leased out. But what you might not know is that, in many cases, this empty ground-floor retail is the unintended consequence of policies that urbanists have cheered on for years.

Today, many major cities require ground-floor retail for new apartments and offices. More commonly, as in the commuter suburbs of New Jersey, incorporating ground-floor retail is a necessary condition for receiving the variances and rezonings needed to construct apartments and offices, particularly near transit.

How did we get to this point? The goal, in itself, isn’t unreasonable. As Jane Jacobs observed, ground-floor retail can add a lot to a neighborhood. Where it works, it activates streets, improves safety and, at its best, makes car-free living possible. Having seen and experienced great streets and neighborhoods with ground-floor retail, urbanists today assume that to build a great neighborhood you need to have a lot of ground-floor retail. Ignoring that causation may work both ways here, they settle on the easiest solution: mandate it wherever possible. The result is the empty storefront blight that we now see in cities across the country.

The trouble with these mandates is that they are instituting an outcome—ground-floor retail—where the processes to make that outcome sustainable aren’t present. In order to make ground-floor retail work, you need at least three things: developer expertise, an existing retail corridor, and sustainable retail market rents.

Criteria #1: Developer Expertise

Before any mixed-use project can get underway, you need developers with experience building and managing mixed-use urban retail. We often lump “developers” in together like they all do the same thing, but really we should think of them more as farmers, specializing in specific products and regions. Foisting urban mixed-use retail onto a market-rate or affordable housing developer is like asking a family-run orchard farmer to set aside a quarter of her budget to cultivate potatoes. If it doesn’t make the whole enterprise unprofitable, it will at least force the farmer to take a big hit and provide a sub-par product.