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Reflective Roof Coating

Technology Snapshot & Benefits:
According to ENERGY STAR®, Americans spend about $40 billion annually to air condition buildings - one-sixth of all electricity generated in this country. In areas that are sunny and warm for most of the year, or have a very hot summer, the costs to individuals are particularly devastating. Reflective roof coating is protective coating that can be applied to roofs to keep a home cool without having to use as much air conditioning. Reflective roof coating is also called albedo coating, since the materials used have high albedo, or ability to reflect the sunlight. Reflective roof coatings have other benefits as well: they can increase efficiency in some air conditioning and ventilation units on the roof and because UV radiation expedites roof ageing, they also slow roof decay. These special coatings work by reflecting the sun's light and releasing absorbed heat.

Reflective roof coating is most effective for flat roofs because flat roofs usually absorb more energy than slanted roofs. The effectiveness also varies with the thickness and color of the coating, with lighter colors and thicker coatings being significantly more effective. In fact, bright white reflective coatings can have a solar reflectance of 85 percent and cut a roof's cooling load up to 70 percent.

Reflective roof coatings can be made from various materials. Paint-on coatings include acrylic paints, polyurethane, and elastomeric. These types of coatings do not require professional installation. Single-ply reflective sheets made from plastic, PVC, or rubber are effective, as are reflective roof tiles made from concrete, clay, or metal. In terms of total cost (raw price, installation fees, and maintenance fees), white titanium dioxide paint and aluminum sheets are the best choice. However, elastomeric and acrylic coatings reflect a higher fraction of solar energy. Longevity of the material used should also be considered.

No matter which materials are used, most homeowners who employ reflective roof coating experience cooler indoor temperatures and lower cooling costs.

Estimated Cost Savings:
Reflective roof coating can cut cooling costs from 10 to 70 percent depending on the coating used, climate, and the degree of sunlight to which the roof is exposed. Hot areas that are sunny for a majority of the year benefit the most from reflective roof coatings. The decrease in monthly energy bills far outweighs the costs of installation. Coatings that are painted on typically cost $15 to $25 per gallon and can be applied by the homeowner. Professional installation of single-ply roof sheets or tiles typically costs the same as installing any other type of shingle or tile; so, if installed at the initial building of a home or rebuilding of a roof, there will be little to no extra cost for the homeowner. Cost for single-ply PVC membranes averages $3 per square foot.

Issues:
Reflective roof coatings are a simple way to cut costs and help the environment. Virtually all roofs can be made to absorb less heat and reflect more sunlight using some type of reflective roof product. However, if the roof membrane is decaying, the coating will not be as effective and it is recommended that the membrane be replaced before the coating is applied. It is best to consult a professional or product manufacturer about the ideal type of coating for a specific roof.

Regional Issues:
Reflective roof coatings are not recommended for areas that are cool or cold for much of the year and/or experience high cloud coverage. They most benefit people in areas that are warm and sunny for most of the year. In warm and/or sunny cities, this coating can help fight the "urban heat island" effect, or increased temperatures due to greater reflectance and absorbance of sunlight by a conglomeration of dark, metal buildings. Decreased indoor temperatures in areas that can become extremely hot can increase comfort and reduce the likelihood of heat-related illness or death.

Installation:
Paint-on coatings are applied using a roller, a brush, or airless spray equipment, and require minimal skill to apply. The roof should be properly cleaned before applying the coating. It is important to consult with the coating manufacturer for tips and advice on how to apply a specific coating to a specific roof. Single-ply reflective shingles and roof tiles must be installed by a professional roofer.

Videos On This Topic:

Install of a Supertherm White Roof (10:02) - Sierra Club Green Homes - The Obama administration is looking to paint roofs white to increase energy reflection and minimize absorption and transfer of heat through the roof.  In this video from Sierra Club Green Homes, watch a typical installation of a white, reflective roof coating and learn more about how this can help save on energy bills

For more information on this topic:

Reflective Roof Coating Institute

ENERGY STAR® Reflective Roof Products

U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy: Cool Roof Calculator

 


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