The Best Coating Material for Tin Roofs

Cool Roofs

• Building codes and the EPA are increasingly requiring “cool roofs” as a way of saving energy. A good roof coating, commonly a light color, should reflect ultra-violet and infrared rays and heat. A reflective roof coating lowers air conditioning costs and extends the life of the roof by reducing stress. Traditionally, white roofs were considered coolest, but recently developed pigments result in colors other than white can be used for a cool roof. The Cool Roof Rating Council lists highly reflective colors. The EPA’s Star Energy program also issues guidelines for coating reflectivity.

Expansion and Contraction

• Metal roofs expand from heat and contract from cold. This can cause screw holes to expand, leading to leaking. A roof coating should be able to expand and contract with changes in the weather. “Elastomeric” on a brochure or label means that that a roof covering is able to expand and contract without cracking or splitting. Most fluid and spray coatings are elastomeric.

Asphalt

• Hot asphalt was the traditional coating for metal roofs. Asphalt coatings were inexpensive and good at shedding water. Emulsions of asphalt, which can be jet black black or contain aluminum to help reflect the heat and ultra violet rays, are still widely used.

Foams

• Spray foams of polyurethane, silicone or acrylics, which appeared in the 1970s, are useful for metal roofs. These foams are thinner and weigh less than asphalt, and they provide a seamless, watertight seal over the entire roof. High-end polyurethane coatings are especially effective for reflecting ultra violet rays, while less expensive polyurethane coatings age more quickly and are prone to yellowing. Polyurethane and silicone foams are best if your roof is exposed to corrosive chemicals. White acrylic coatings, which are even more useful for cool roofs, appeared in the 1990s.

D6083 Acrylic Foam

• The most typically applied coating for metal roofs is D6083 acrylic foam. D6083 means the foam meets the requirements set by the American Society for Testing and Materials that sets international standards for building materials. Acrylic foams may not adhere to Kynar-500 and silicone coatings on some metal roofs.