Constructing new buildings generates a lot of planet-warming emissions. Zero-Net-Energy (ZNE) buildings don’t add operating emissions, but these structures still have a huge and immediate carbon footprint — the carbon emissions from the mining, transportation, manufacture, and placement of all the materials that go into a building. Each year, the U.S. adds about six billion square feet of new efficient, code-compliant structures. The emissions from all the materials and processes to erect these buildings is roughly one percent of total U.S. greenhouse gas (GHG) emissions. In addition, they will generate about five percent of total GHG emissions each year from operations. But these figures are dwarfed by the operating emissions of all existing U.S. buildings, more than a third of total annual emissions. In brief, because of the urgency of climate change, the focus needs to be on existing buildings.
The total embodied emissions from materials in an existing structure have already happened. From a climate change perspective, we cannot afford to release that amount again by replacing old buildings with new ones. Yet, we knock down old buildings because the land has become more valuable, or the style is outdated, or because building anew is often easier than renovating existing structures. Renovating a building, however, releases 50-75 percent less carbon than a comparable new building, and if the renovation includes a deep energy efficiency upgrade, there is an even bigger reduction in GHGs. When renovations join with major energy upgrades then both embodied and operating emissions are reduced, money is usually saved, carbon almost always saved and in some cases zero-net-carbon can be achieved.
There are three basic parts to making an existing building net-zero: