Customers often ask me if painting their asphalt shingle roof white will make a difference in their cooling bill. To answer that question I used an infrared thermometer gun to compare the surface temperatures of a cedar colored asphalt shingle and another shingle on the same roof that had been painted white. These temperature readings were taken on a sunny April day in Houston at 3 pm, (outside air temperature was 83°F). The picture below shows the results.
As you can see, the unpainted section of this roof is 173.3°F, while the section painted white is just 128.8°F. The painted shingle is 44.5°F cooler than the regular shingle. That’s a pretty significant difference in surface temperature, and I have no doubt that if the entire roof was painted white, not just two shingles, the white shingle temperature would be even lower.
Also, if the home had darker shingles, as most homes do in this area, the unpainted shingle temperature would be much higher. I’ve been on dark-gray asphalt shingle roofs in August that read over 190°F.
Painting Your Roof White Works, But…
Painting your asphalt shingle roof white can indeed make your roof surface 45-80°F cooler under the hot Texas sun, and this should easily cut your cooling bills by 10-15%.
But there are problems with this approach, mainly finding a paint that will adhere to the asphalt shingles and last for more than a few years. In the experiment above, I used an ordinary latex paint and it’s already flaking off a few weeks later. By comparison, the paint on cool metal roofing panels can last for 30 years or more.
White colored metal roofs have an initial solar reflectivity rating in the mid 80′s, whereas darker colored asphalt shingle roofs have a solar reflectance rating below 10. But if you really want to reflect the sun’s heat, you need a properly installed radiant barrier above your roof deck (not in the attic). With an above-sheathing radiant barrier, roof color becomes a less critical factor in the overall thermal performance of the roof. This is good news for homeowners who are not thrilled about having a white roof.
Learn more about cool roof design by clicking here: Cool Roof Design for the Hot Texas Climate