Imagine two brand-new houses standing side by side in the same neighborhood. Same size. Same layout. Same blazing California sun overhead. The only real difference between them is the roof: one is topped with dark asphalt shingles, the other with light-colored reflective tile. Now imagine keeping track of all the changes in temperature and all the electrical power that these houses consumed throughout the entire year. That was roughly the case in Fresno, where the findings showed how much your roof can affect comfort and power bills. The study from Lawrence Berkeley National Laboratory, ‘Measured temperature reductions and energy savings from a cool tile roof on a central California home,’ found that the home with the reflective tile roof used much less cooling power compared to the other house, although both houses were exposed to the same weather conditions.
A real experiment, not just a computer model
Simulations have been the basis for the majority of all research performed on roofs, but that is not the case for this study. Researchers chose two single-story houses constructed side by side in Fresno, California, in 2010. One of the houses had a typical dark asphalt shingle roof that was low in reflectivity, while the other had a high-reflectivity concrete tile roof with an air gap. Data was collected for almost a year, from May 2012 to April 2013, on the temperature of the roofs and attics, as well as how much air conditioning was used in each house. Researchers chose Fresno because it sits in California's Central Valley, where homes typically use air conditioning from May through October.
The heat difference was hard to ignore
On a representative sunny day in July, the researchers noticed a marked temperature difference: the reflective tile roof's surface reached a peak temperature 13.8°C lower than the peak temperature of the dark shingle roof that day. In addition, the attic space under it had a temperature that was 10.5°C cooler. This difference matters because attic temperature can affect indoor room temperature, forcing the air conditioner to work longer to cool the home. Over the summer season, the surface temperature of the tile roof was approximately 3.4°C lower than the shingle roof. It's worth noting that the tile roof wasn't just a different color; it also had a ventilated air gap beneath it and nearly twice the thermal mass of the shingle roof. The study's own authors acknowledge that their design didn't fully separate these three factors, though their analysis points to the ventilation gap, more than the color change or the added mass, as the biggest driver of the daytime cooling difference.
