Last spring Dr. Chu, US Energy Secretary, advocated for "white roofs everywhere". He said lightening roofs and roads in urban environments would offset the global warming effects of all the cars in the world for 11 years. Unfortunately, I’ve discovered that blanket statements like that need to be more closely examined before blindly accepting them even from Nobel Prize winning physicists working for the government. Both Lawrence Livermore Laboratory and Con Edison performed studies of different roofing materials. Livermore Lab only looked at the reduction in energy used for air conditioning probably because their Lab is located in California.
Con Edison divided their training center's roof into three parts: a traditional dark roof section, a section painted white, and a green section with plants growing on it. An energy-efficiency study by Columbia University was designed to help researchers understand how each kind of roof performs. The green and white roofs were found to perform equally well in preventing the “heat island effect,” in which conventional dark roofs absorb sunlight during the day and radiate heat back into the atmosphere at night which is postulated to create along with asphalt pavement the increased temperatures associated with urban and suburban areas.
However, the green roof is beneficial in summer and winter as well as reducing rain water runoff. The green roof reduces summer heat gains by up to 84% and winter heat losses by up to 37% compared to a black roof. The white roof reduces summer heat gains by up to 67%, but reflects heat in the winter when it is desirable to maintain heat. In a cold climate, a dark roof can lower heating costs by soaking up the winter sun. White-roof advocates counter that, in the continental United States, the "winter penalty" is just 10 percent of the overall savings because the roof is covered with snow for much of the winter, but many locations with freezing or near freezing temperatures do not have significant amounts of snow throughout the winter.
Green roofs are clearly the better choice for energy consumption year around. The obvious problem is green roofs only work with flat roofs, my house has a traditional peaked roof so a green roof is not really and option. I can not even imagine my neighbor’s reactions to a white reflective roof glaring at all drivers from the end of the cul-de-sac. Another problem I did not even imagine is maintenance requirements for a green roof. I went to see the Wetland Studies and Solutions, Inc. building in Gainesville, VA which was one of the first LEEDS certified buildings in Virginia and was dismayed to discover that weeding and replanting after extreme weather was necessary. WSS actually utilizes its interns to weed the roof. I can barely keep up with the hand weeding of my garden (because I do not use weed killers or other chemicals, I dig out the weeds in my beds).
Living in a moderate climate (last winter not withstanding) my roof does not spend the greater part of the winter covered in snow and I might benefit by having my roof absorb heat in the winter. Though, throughout the summer a dark roof would results in extra load on the air conditioning/heat exchanger. One of my goals in the insulation of my attic was to thermally isolate the attic from the rest of the house. For the insulation project, the attic and accessible areas of the basement and crawl spaces were inspected for adequate insulation. Then following the recommendations by the Oak Ridge National Laboratory the attic, crawl spaces, eves, ductwork, underside of a large portion of the main level floor were insulated with cellulose. The pipes, end caps, knee wall, sump pumps and all identified areas were sealed, the garage was insulated and an insulated garage door installed. My total electricity bills for the following 12 months were 27% less than I paid in the 12 months before I added the additional insulation to the house, and the winter liquid propane usage (as measured in volume use December through March both years) was reduced by 25%. Also, the overall comfort in the bedroom over the garage and the master bedroom has been vastly improved. I was very surprised at the energy savings for what was a well insulated home. The payback on this project was under 4 years, unbelievably good.
My solution to the roof question was to begin to fill the southern roof span with solar panels. I have covered about 60% of that span with solar panels (so far). The goal is to test their production and function and save up more money for more panels down the road, though my estimate is that the savings from the solar panels will be about the same as from the insulation project. The problem is they cost (before rebates, tax credits and sale of SRECS) ten times as much. A more cost effective next step would be to convert the entire house heating and cooling to “geothermal” heat exchangers, though in truth, I have yet to find any models to estimate my cost and savings from that conversion.
Other recommendations for sustainable living or energy efficiency are based on a set of assumptions that may not be true for all situations. People’s patterns of living are starting to diverge. As an example we live, work and relax from home. I leave the house a few times a week to purchase supplies, pray, and volunteer. I rarely go more than 10 miles from home and drive (my little hybrid) only a few thousand miles a year. My water supply and waste disposal are private and sustainable. According to research performed in Dutchess county the average daily aquifer recharge (from rain and snow only excluding septic recycling) for Soils types C, C/D and D prevalent in this part of Virginia are estimated 326-583 gallons per acre. It is essential in a sustainable system that the groundwater level be maintained with recharge and adequate surface water is supplied to maintain the ecology even during drought years. My property totals more than 10 acres and our total indoor and outdoor household water usage was clocked during the early summer at between 100 and 150 gallons a day. We do not water our garden; trying to plant only what will thrive in the natural environment unaided. Virginia gets plenty of rainfall and it seems silly to plant anything that requires irrigation. Thus, not only is my septic system non-consumptive, the recharge rate vastly exceeds our water usage (and hopefully our neighbors since our water supply is dependent on total demand and recharge of the aquifer). I have an alternative septic system and I am incredibly careful of its operation, management of the load and maintenance.
Yet, with that I use a large amount of electricity for entertainment, to store my meat bought in bulk and the wine put up for the next decade. Thought my refrigeration units are energy star, there are several of them. Our home theatre is an LCD which is far more energy efficient that plasma, but less energy efficient than the now available LED TVs. It may be an LCD, but its large. Sustainable living is about thoughtfully using the earths resources. A fun place to start thinking about the sustainablility of your life is to go to the energy star home page and measure your home energy score.