We have so much building stock existing that we can't just demo and redo. Like we have to be using these existing buildings. In one for one reason, primarily like from a climate change perspective, there is so much embodied energy in those existing buildings that we would basically be like releasing out into the atmosphere if we demo to them. And if we were crushing those materials down and putting more energy into making them something else, or they would go sit in a landfill. And we're also offsetting future carbon needed. By not needing to build a new building because we already have something existing. So they'll like automatically the amount of carbon we're using is way lower if we're starting with an existing building. http://www.solvecast.com/articles/detail/15258-sustainable-design-resilience-planning-with-ariane-laxo