What is the most efficient roof?
What roof is the most energy efficient for a home? I've heard that lighter shingles are better, and that a sod roof is the best, what practical advice can you offer?
Answer - Best answer on Yahoo! Answers
The best roof design from an energy efficiency perspective is a green, living roof or rooftop garden, because it provides both an excellent level of insulation from heat loss in the winter (it works out to something like R60) and has enough thermal mass that it can absorb summer heat during the day and radiate it back outwards at night
Green roofs are generally built flat and include a thick layer of insulation, a reinforced and impermeable surface, and a layer of soil more than a foot thick. In summer the roof has an automated sprinkler system that waters the plants growing there. This water both cools the soil (and therefore prevents heat from getting into the house) and gives the plants moisture to evaporate (which further cools the air around the roof, preventing more heat absorption).
In winter the water is of course turned off and chances are the plants are all dead (at least if your winters are cold, like mine are in Toronto, Canada). But that thick layer of topsoil, with a thick layer of insulation below that, adds up to very little heat escaping out your roof.
If you have a traditional home and adding a green roof is not an option, I'd suggest a regular roof with light-colored shingles (in a warm climate) or dark-colored shingles (in a particularly cold climate where air conditioning is never needed, such as northern Ontario Canada). Light colored shingles will reflect sunlight and prevent attic overheating, while dark colored shingles will absorb sunlight, which helps if you have the heat on most of the year. You can even buy specialized roofing paints that not only brighten your shingles to increase their reflectivity, but that will extend the life of standard asphalt shingles.
For a roof with attic, make sure you have adequate ventilation at both the top and bottom of the attic (in the soffits and along the ridge or at the peak) so that the natural airflow of warming air from below to above draws the hot air out and pulls cooler air in.
Finally, adequate attic ceiling insulation is important in all cases. Depending on the temperature zone you live in, you should have somewhere between R-38 and R-60; the higher the better. Even if you only use an air conditioner and never need to have heat on, a higher R value will keep the heat from your roof out of your house.
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