Green for its own sake
Constructing new LEED-certified green buildings is all well and good, but if they're further from your workers' homes and you have to tear down perfectly good old buildings to do so, the hoped-for energy savings are wasted.
Embodied energy. Another term unlovely to the ear, it's one with which preservationists need to get comfortable. In two words, it neatly encapsulates a persuasive rationale for sustaining old buildings rather than building from scratch. When people talk about energy use and buildings, they invariably mean operating energy: how much energy a building -- whether new or old -- will use from today forward for heating, cooling, and illumination. Starting at this point of analysis -- the present -- new will often trump old. But the analysis takes into account neither the energy that's already bound up in preexisting buildings nor the energy used to construct a new green building instead of reusing an old one. "Old buildings are a fossil fuel repository," as Jackson put it, "places where we've saved energy."
If embodied energy is taken into consideration, a new building that's replaced an older building will take up to 65 years to start saving energy...and those buildings aren't really designed to last that long.