Whether you're building a new home or performing upgrades and remodeling, you likely want to consider incorporating ideas that help lower power bills. You have numerous options here, such as window coverings and HVAC systems. Another effective means of lowering your energy consumption is installing a cool roof.
Cool roofs reflect sunlight and absorb less solar heat than a standard roof, lowering the temperature of your roof and therefore your home. Materials vary, as do efficacy and price.
Solar reflective shingles typically include three layers. The fiberglass layer adds insulation, the asphalt layer provides protection, and the top layer reflects sunlight.
Cool roofs offer a variety of benefits for both residential and commercial buildings. They help decrease cooling bills by lowering internal temperatures, lower the temperature in areas without air conditioning, and typically extend the life of your roof. They even help lower air temperatures, benefitting the environment.
These benefits all arise from the cool roof's surface temperature being significantly cooler than a traditional roof, to the tune of 50 degrees or more during summer months. This helps lower ambient temperatures within the home, which helps reduce cooling bills and keep spaces without air conditioning cooler.
The degree of savings and lower internal temperatures relies on a variety of factors, including the type of HVAC system you use, the amount and quality of insulation within your roof, and your local climate.
Whereas darker traditional roofing materials absorb sunlight, the reflective surfaces of a cool roof reflect it away. This results in lower absorption of solar heat and a cooler roof.
Roof temperature is rated via solar reflectance and thermal emittance, with ratings ranging between 0 and 1. As in golf, the higher the rating, the lower the temperature. Darker roofs score very low on these scales, absorbing nearly all of the sun's rays (around 90 percent). Summertime roof temperatures, especially in warmer climates, regularly reach 150 degrees, especially with roofs in darker colors. Roofs with lighter colors absorb less than half the amount of solar energy. The solar reflectance rating represents the fraction of sunlight reflected by the roof. Light colored roofs reflect between 55 and 90 percent of sunlight reaching the roof surface, giving them solar reflectance ratings between 0.55 and 0.90.
The thermal emittance rating represents cooling efficiency via thermal radiation. Also measured on a scale between 0 and 1, with 1 representing perfect efficiency. Non-metallic surfaces have higher thermal emittance ratings, typically within the range of 0.80 and 0.95. These ratings indicate a surface that cools easily and quickly. Shiny metal surfaces have lower ratings, keeping them warm longer.
Ideally, if you are looking for cool roof materials, choose those with higher ratings.
Determining cost depends largely on the slope of your roof, though many homeowners prefer to not paint a steeply sloped roof white for aesthetic reasons. Another factor is whether you opt to use standard roofing materials in light colors or install solar reflective shingles.
Solar reflective shingles range between $2 and $3 per square foot, depending on manufacturer and vendor. These typically come in mid-range colors, such as medium browns and grays. They have higher solar reflectance ratings than darker materials, but much lower ratings than a white roof, ranging between 0.25 and 0.30. However, their thermal emittance ratings are excellent, typically around 0.95.
If you'd like to calculate potential energy savings, use the Roof Savings Calculator. Choose your building type (residential or commercial), and then answer some multiple-choice questions regarding building size, location, HVAC equipment, and current roofing.
Installing a cool roof saves money on your energy bill during the summer. However, if you live in a cooler climate, and the majority of your energy costs come in the form of heating your home, installing a cool roof is not likely to save you money on your utilities. This is because the same technology that keeps your home cooler in the summer also keeps it cooler in the winter.
The Cool Roof Rating Council provides rebate and incentive program information for both residential and commercial applications. Numerous states throughout American offer incentives for people and businesses going green. If you choose to install a cool roof, don't forget to check this page, or talk to your roofing contractor, to determine which incentives your qualify for.
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