Whether intended to help save the world from global warming or just to lower electric bills, roof materials are in the news. “Cool roofs are made of materials… that reflect much of the sunlight they receive back into space. Green roofs incorporate vegetation to keep a building cool and provide moisture to the atmosphere that cools their surroundings.” (CSM) While not every roof can be retrofitted and new construction seldom uses these types of roofs, scientists have modeled what might happen if every roof were suddenly cool or green. Which would be “better”? It’s not obvious. Cool roofs may lower summer air conditioning, but increase winter heating bills. Green roofs are heavy and can be difficult to construct, but by holding moisture they may increase local rainfall. Either way, roof choices will have an infinitesimal effect on global warming, so the immediate impact on the building’s residents will dictate which is best. That, and your budget.