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What are Reflective Roof Coatings?
Reflective roof coatings, also known as albedo coatings, are products applied to roofs to reduce solar heat, especially in areas with hot, sunny weather for a good part of the year. Because they can reduce surface temperatures by up to 80°F (about 45°C), these products also have a big impact on cooling costs. The Lawrence Berkeley Laboratory in California estimates that reflective coatings can save homeowners a minimum of 25% in energy usage.
Another advantage of reflective roof coatings is that they contain UV-blocking pigments. Because UV rays age a roof considerably, the use of reflective coatings can extend the roof's life by up to 15 years. This is especially true in buildings with low slope or flat roofs, which tend to absorb sun energy at a higher rate than slanted roofs. Since roof maintenance accounts for more than 80% of a building's total maintenance cost, any product that can extend roof life will result in substantial savings.
Reflective roof coatings act like mirrors, reflecting the sun's radiant energy back into space. To rate the level of reflectiveness of different products, manufacturers have come up with a classifying system. High-albedo products such as bright-white paint are the most effective, with a solar reflectance of 85%.
Some of the materials used for coating roofs include: elastomeric, polyurethane, and acrylic paints; single-ply roofing sheets made of rubber, plastic, or PVC; clay or concrete tiles; and metal, available in both natural and dark-colored sheets. Some materials can be easily applied with a roller, as in the case of paints, while others, such as PVC sheets, require the use of caulk or heat sealing done by a professional. If cost is a consideration, white titanium dioxide paint and aluminum sheets are the best choices. They are inexpensive, easy to apply, and require little maintenance.
Since 1998, the Cool Roof Rating Council, or CRRC, provides Energy Star labeling to roofing products that pass their quality tests. Because roof coatings tend to lose their reflectance properties over time due to dust and dew, regular maintenance, in the form of reapplications or cleanings, is a must.
Costs for reflective roof coatings vary from $0.75 US Dollars (USD) per square foot for acrylic paints to over $3 USD per square foot for PVC single-ply membranes. Price usually includes both materials and installation. While the up-front price of roof coatings is usually higher than that of a traditional roof, the savings on energy bills more than justify the added expense.
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Discussion Comments
1) If white titanium dioxide paint and aluminum sheets are more cost effective, why not address these in the article? Is there any reason for not applying titanium dioxide paint? How long will it last? How do "high-albedo products such as bright-white paint are the most effective, with a solar reflectance of 85 percent" differ from white titanium dioxide paint?
2) What type of aluminum sheeting? Solid, or heavy duty reflective mylar sheeting? What's the best way to apply the sheeting? Stapling?
Thanks for taking the time to answer these questions. Need to reduce heat to a slanted roof in N California.
Great info. thanks.
No. Winter heating of interior does not come from heating of the roof. What you'll probably notice, though, is that it will take a lot longer for the sun to melt any snow that falls on a white roof. But snow will reflect the heat both ways so it might help somewhat with winter insulation, odd as it may seem. Think igloos.
anon33892: to much less of an extent. In the summer, the sun is higher in the sky, which means your roof is more directly hit than the south wall.
In the winter, the sun is lower in the sky anyway, and the south wall gets more direct sun than the roof. Also, since heat rises, it doesn't do as much good to have a dark roof expecting to save on heating costs than it does to have a reflective roof to save on cooling costs.
Yeah it should.
Does reflective roof coating reflect the sun's energy in the winter also, causing your home to be unusually cold?
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