Everyone I know is talking about "green roofs" and "living roofs." Does it make more sense to put a green roof on top of a building, or to install photovoltaics to generate energy?

Gil: Isn't it grand to have too many good choices instead of too few? But as is often the case, the either/or question is often the wrong question. (See "The Trap of Binary Thinking.")

Leslie Hoffman of EarthPledge (publisher of the beautiful book, Green Roofs: Ecological Design and Construction) suggests that "there is no reason that they cannot be integrated into a symbiotic installation." Steven Peck of the Green Roof Industry Association concurs: "Integrating the two systems by placing a PV panels above an extensive system can increasing conversion efficiency by as much as 25%. Green roofs lower the ambient temperatures thereby allowing more efficient PV conversion."

Jerry Yudelson of Interface Engineering goes further, suggesting that:

"techno-fixes" such as the currently popular green roofs and photovoltaics may be taking us away from intelligent thinking about sustainable design and green buildings... [since] reducing demand is always far more cost-effective than increasing supply.

The article is well worth reading, since it systematically lays out options, priorities and tradeoffs, and argues for an integrative design approach, rather than the piecemeal, thing-focus approach that often passes for "sustainable design." Writes Yudelson:

For example, siting the building trumps everything else.

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Gil Friend, systems ecologist and business strategist, is president and CEO of Natural Logic, Inc. -- offering advisory services and tools that help companies and communities prosper by embedding the laws of nature at the heart of enterprise. Sign up online to receive his monthly column via email. Read Gil's blog here.