The city of Chicago recently announced that the Sears Tower and the Merchandise Mart are being retrofitted to meet LEED certification standards, making the Sears Tower the largest green structure in the United States. News link.
This is a trend that will obviously continue. Due to the vast number of built-to-code structures already existing, it wouldn't make any business/economical sense to knock everyone of them down and build it back green. Green retrofits are a good solution; however, you have to crunch the numbers. I am sure there are some projects out there that would be better off bull-dozing and starting from scratch. You also have to be aware of the public's desire for preservation. The architectural fabric of a particular city can take decades to build and tear-down strategies are often met with public resistance.
I would be curious to hear from any of you that have done a green retrofit...whether it be a commercial structure or a personal residence. Did it cost more than you anticipated? What were some of the obstacles? How did the project turn out?