Richard Beckett, another director of the BiotA lab, says that he’s interested in the project flipping the usual way that buildings are designed, at least in a small way. “Traditionally architecture is a top-down process, you decide what the building will look like, and then you build it. Here we’re designing for a specific species or group of species, the material and geometry we’re using is so specific that it only allows certain species to grow.” It’s controlled chaos.

Both Cruz and Beckett talked about a particular way of thinking about their buildings that they said was different from most architects. “Every architect you speak to talks about the skin of the building,” says Beckett. It’s this metaphor that everybody uses in completely different ways.” But they want to propose a different way of seeing things. Instead of skin, the lab wants people to think of the exterior of a building as bark. “Not just a protective thing, a host; it allows other things to grow on it, it integrates as well,” says Beckett. Here’s how Cruz explains it: “Barks are mediators between the internal conditions of a tree in which all sorts of species can grow on this bark and enrich the environment with an ecology that’s unthinkable without bark.”

In the larger scheme of things, the BiotA work fits in with the recent push to “green” buildings and architecture. Often those efforts come by way of things like living walls full of plants, or green roofs. But these living systems can be expensive and hard to maintain. Sometimes all the plants die, and have to be replaced.

Cruz tells a story of a plant nursery in East London that had a green wall. “When I saw it for the first time, I thought it was wonderful!” he says. But six months later when he passed the nursery again, he noticed that the plants were all dead and falling off the wall. “A year later, much to my surprise, they were putting up steel panels with photographs of a forest on them,” he says, laughing. Basset and Cruz say that their system is far lower maintenance. Lichens and mosses want to grow on things anyway, and require very little upkeep.

The idea of bringing nature into cities might seem normal to people today—parks and gardens and green roofs are scattered across many of America’s cities. But the idea of including green spaces in a city is a relatively new way of thinking about urban life. “The idea of including nature inside of a city is a pretty foreign concept to most urban cultures from the 18th century all the way back,” Benjamin Stanley, who studies the history of urbanism, told me. Previously, when nature was included in urban settings, it was for a specific purpose: sacred trees, plots for growing food, hunting land to show the wealth of a monarch. The idea of including nature in the design of our buildings—as a decorative element, as a way to soften cities, or connect people with nature—is new, and represents a profound shift.