Dear Angie: Will light-colored roofing keep my house cooler? I have read that roofing material that reflects light will make it easier to cool a house in the summer. Some people even paint their roof with special white paint to reflect sunlight. My flat roof is covered with a dark membrane that needs to be replaced. The roofer who installed it says the material is reflective, but it looks black to me. The membrane does have some light-colored grit embedded in it, but the overall appearance is dark as night. Is the roofer blowing smoke? — Rick B., Rolla, Mo.
Dear Rick: It is true that the darker the color, the more radiant heat your roof will absorb. A variety of roof coatings and paints can lighten a roof's color or offer more reflectivity of solar heat. Solar reflectance is the key to getting the highest energy savings in warm months. You should be able to find out the reflectivity rating of your existing roof, or a new one, through its manufacturer.
The higher the solar reflective value, the more efficient the product is in reflecting sunlight and heat away from the home. A white granulated roof coated with white elastomeric paint, for example, will reflect about 96 percent. Some silver- or metallic paints can be applied to the inside of the roof deck and can help block as much as 75 percent of the heat coming in. If you do add a reflective coating over the existing membrane, first check with the existing roof's manufacturer to ensure that by doing so, you will not void any remaining warranty.
More important than your roof's color, though — as it relates to heating and cooling — is having adequate ventilation and insulation. With a properly vented attic space, the difference in heat transfer from a dark to a light shingle is minimal. Having good reflectivity, though, can prolong the longevity of many roofing membranes.
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If you are truly concerned with reflectivity, make sure whatever roofing product you use is Energy Star rated, so it is guaranteed to meet minimum solar reflectance values. Energy Star roofs can be as much as 100 degrees cooler on the roof surface and can help reduce cooling demand by 10 percent to 15 percent.
Ultimately, any energy savings that can be achieved with reflective roofing are highly dependent on your home's design, the amount and type of insulation, the climate and its overall energy efficiency. Talk to multiple roofers about your options. Ask for examples of their work with reflective roofs, and discuss which characteristics are best for your home and climate.
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