What if the Greenest Building Isn't the One Already Standing?

Right at the beginning of this TreeHugger article by Lloyd Alter, the reader has been warned of forthcoming heterodoxy:

For years, this TreeHugger has been a proponent of preservation and renovation rather than demolition and replacement. But over the years I have renovated my own house twice, added a bit of insulation here and there but not enough to make a serious difference, because I wanted to retain that historic character of the wood and the windows. In the process I have probably spent as much money as I would have had I knocked it down and replaced it, and I have now "locked-in" fossil fuel consumption and carbon emissions, even though I pay a premium for "green" Bullfrog power and gas.

According to Alter, that choices were contrasted with a recent project by Bryn Davidson of Lanefab, which demolished an "asbestos laden fossil fuel hog" in favor of a new passive house. The key point for Alter is the "locked in" nature of emissions connected to buildings. Unlocking emissions from existing buildings is "really expensive and challenging," according to Alter.  

"I keep saying, 'The greenest building is the one already standing,' but if we want a world of zero emissions, along with increased density and affordable housing, we might have to give up a bit of that "neighbourhood character" or other similar excuses that are often used to prevent new housing from being built, and learn from Byrn."