Passage2For most architects, moss and lichen growing up the side of a structure is a bad sign. Building materials are designed specifically to resist growth, and much research has been done to develop paint treatments and biocides that make sure the concrete and wood and bricks that sheath a buildingaren't colonized by living things. But a new group is trying to change all that. Instead of developing surfaces resistant to moss and lichen, the BiotA lab wants to build facades that arebioreceptive.BiotA lab, based in University College London's Bartlett School of Architecture, was founded last year. The lab's architects and engineers are working on making materials that can foster the growth of cryptograms, organisms like lichens and mosses. The idea is that ultimately they' ll be able to build buildings onto which a variety of these plants can grow. Right now, they' re particularly focused on designing a type of bioreceptive concrete.Marcos Cruz, one of the directors of the BiotA lab, says that he has long been interested in what he sees as a conflicted way of thinking about buildings and beauty:We admire mosses growing on old buildings, we identify them with our romantic past, but we don't like them on contemporary buildings because we see them as a pathology,he says. Cruz says that he wants the BiotA project to push back against the idea that cleanliness is the ideal that buildings should strive for.Architects were wearing a straightjacket that only in the last 20 years architects started shredding off.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 thinkof 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 greenbuildings 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 BiotA lab wants people to think of the exterior of a building as_______.