Installing a roofing material that stays cool in the hot sun is a core element of a green building. That is why numerous research groups are working on finding the perfect material that is inexpensive, durable, and has the appearance of a traditional darker-colored roof, while also reflecting the hot sun as effectively as a light-colored material.

Roof manufacturers are reluctant to offer lighter-colored roofing materials because customers typically want darker colors like dark green, brown or black. (Image courtesy of Hawaii Renovation.)

Researchers from the Heat Island Group at the Lawrence Berkeley National Laboratory (Berkeley Lab) have found that the application of synthetic ruby red crystals is surprisingly effective at reflecting heat. They are currently conducting more research to determine if the application can provide all the aesthetics, structural integrity, affordability and effectiveness of a green roof coating material.

The researchers experimented with using pigments of ruby red crystals to create a fluorescent effect. What they found is that certain pigments can help roofs stay as cool as commercial white coatings. Their findings are published in the journal Solar Energy Materials & Solar Cells.

These results were a significant breakthrough for the researchers, as they have been experimenting with various pigments over the past 15 years. The researchers state that using fluorescence, or photoluminescence, for cool materials is a new initiative.

The testing of fluorescent material took off when Berkeley Lab scientist Paul Berdahl purchased some synthetic ruby red crystals online. He then applied them to a white coating and exposed them to bright sunlight, and found that they stayed cooler than an off-white colored surface.

Berdahl and his team then synthesized the ruby powder using aluminum oxide, which was mixed with varying amounts of chromium to produce several shades of red pigment. After the powders were converted into a paint, they were applied to bright white substrates and exposed to sunlight. Their ability to keep the underlying materials cool has so far proven successful.

Research associate Sharon Chen and scientist Paul Berdahl hold up their prototype coating made from ruby powder and synthetic ruby crystals. (Image courtesy of Marilyn Chung/Berkeley Lab.)

The crystalline powder is applied as a paint on white surfaces. (Image courtesy of Marilyn Chung/Berkeley Lab.)

A roof-coating manufacturing company is currently conducting experiments to test the material’s ability to withstand weathering. The cost of the material is not predicted to be significant. Researchers, of course, don’t expect the average homeowner to be able to afford to attach actual rubies to their houses.

“[The rubies] are mostly aluminum oxide, which sells for about 70 cents per kilogram (or about 30 cents per pound),” said Berdahl. He also believes the durability of the materials will be comparable to other roof coatings.

The team is also experimenting with other fluorescent colors for their ability to stay cool. So homeowners who have always wished for a rainbow-colored energy-efficient house can stay tuned.