The buzzword "GREEN" has really created a lot of confusion. The other day I had a contractor call me asking about our metal roofing EnergyStar. This was a good roofing contractor. He installed some of the finest roofs in my home city of Houston, Texas. But, he did not know. If he does not know, how can you possibly expect to know.
In metal roofing, we have our own buzzword – "COOL." Cool is a word that one of the paint manufacturers came up with to describe this addition to the paint that makes it more reflective. Now, when anyone asks for a "cool" metal roof, contractors heads start spinning. So, I'm going to tell you why you want a white or bare Galvalume metal roof today (not a cool, green one).
If your energy bills look anything like mine, you are constantly thinking of ways to reduce your consumption. When it is time to get a new roof, you are presented with yet another opportunity. Reflectivity and emissivity are big words that are quite simply the evaluation standards for this decision. Emissivity is the measurement of how much heat / cold is radiated through a material. Reflectivity is the measurement of how much heat is reflected away. Our goal is to be affected as little as possible by the outside elements.
The most reflective color is. . . . WHITE! Beyond White, only bare Galvalume will shine brighter. As the colors become darker, the reflectivity becomes worse. Tans and oranges perform better than greens and browns. The more heat that is reflected away, the less heat there is to radiate into your conditioned space or attic. This is the only requirement for EnergyStar roof products. They must have an initial solar reflectance of 0.25 or greater and have a solar reflectance of 0.15 or greater after three years in use.
It's not that simple. So, stay with me. Have you ever stuck your finger on a cast iron skillet with a flame going underneath it? It's pretty hot, huh? It gets a little more bearable the further your hand gets from it. How long would it take to cook pancakes if the pancake did not touch the skillet? Imagine that your roof was suspended slightly above your deck, instead of pressed against it. It would reduce the amount of radiant heat transfer. Guess what most residential roof contractors do not offer to you. On a standing seam metal roof panel, there are many systems where the clip has an offset to separate the panel from the substrate. They are available from 1/4 "to 1" offsets.
My neighbor removed the soffit from his house and claims that his attic is significantly cooler and his electric bill is half of what it was this time last year. It's like opening an oven door. He said that he had vent slots in the soffit before, but the free air passing through now is unbeatable. Other than the beehives up there, it's a brilliant idea. Ridge vents seem to be vastly more popular than soffit vents. You need both to have a flow.
In summary, here's your benefit list when shopping for metal roofing:
1) Initial Solar Reflectance of color selected must be over 0.25, preferably 0.50. Lists of these roof products are available at energystar.gov. It's not the product, but the color and coating type of the product. Emissivity is a more valuable feature in warm or hot environments.
2) Select a product that sits above the deck. Examples include corrugated panels with vertical highs in them (I prefer a hidden fastener system) or standing seam with offset clips.
3) Effective ridge and soffit venting should be a part of the solution as well. Not only is it smart for energy efficiency, it is a powerful tool to prevent moisture collection.
Incorporating these items into your next roof will make your energy bills go down and the corners of your mouth go up.