A cool roof is one that has been designed to reflect more sunlight and absorb less heat than a standard roof. Cool roofs can be made of a highly reflective type of paint, a sheet covering, or highly reflective tiles or shingles. Just as wearing light-colored clothing can help keep you cool on a sunny day, cool roofs material that is designed to reflect more sunlight and absorb less heat than a standard roof. Cool roofs can be made of a highly reflective type of paint, a sheet covering, or highly reflective tiles or shingles. Standard or dark roofs can reach temperatures of 150°F or more in the summer sun. A cool roof under the same conditions could stay more than 50°F cooler and save energy and money by using less air conditioning.Benefits of Cool Roofs
A cool roof can benefit a building and its occupants by:
• Reducing energy bills by decreasing air conditioning needs
• Improving indoor comfort for spaces that are not air conditioned, such as garages or covered patios
• Decreasing roof temperature, which may extend roof service life.
Beyond the building itself, cool roofs can also benefit the environment, especially when many buildings in a community have them. Cool roofs can reduce local air temperatures (sometimes referred to as the urban heat island effect), lower peak electricity demand, which can help prevent power outages, and reduce power plant emissions, including carbon dioxide, sulfur dioxide, nitrous oxides, and mercury, by reducing cooling energy use in buildings.
Types of Roofs and How They Can Be Made Cool
There are many types of roof systems available, but the surface exposed to the sun is the one that determines if a roof is cool or not. You can usually make a new or existing roof cool by selecting the appropriate surface. Cool roof coatings are white or special reflective pigments that reflect sunlight. Coatings are like very thick paints that can protect the roof surface from ultra-violet (UV) light and chemical damage, and some offer water protection and restorative features. Products are available for most roof types.
Low Sloped Roofs
Single-ply membranes are pre-fabricated sheets rolled onto the roof and attached with mechanical fasteners, adhered with chemical adhesives, or held in place with ballast (gravel, stones, or pavers). Built-up roofs consist of a base sheet, fabric reinforcement layers, and (usually) a dark protective surface layer.
How They Can be Made Cool
The surface layer can be made different ways, and each has cool options:
• Substitute reflective marble chips or gray slag for dark gravel in a flood coat of asphalt
• Use reflective mineral granules or a factory-applied coating rather than a dark coating on a mineral surfaced sheet
• Apply a cool coating directly on top of a dark asphaltic emulsion coating.
Steep Sloped Roofs
Shingle roofs consist of overlapping panels made from a variety of materials such as fiberglass asphalt, wood, polymers, or metals.
How they can be made cool: Buy cool asphalt shingles, which use specially coated granules that provide better solar reflectance. (Coating existing asphalt shingles to make them cool, however, is not normally recommended or approved by shingle manufacturers.) Other roof shingles can be coated at the factory or in the field to make them more reflective. Tile roofs can be made of clay, slate, or concrete. Tiles can be glazed to provide waterproofing or coated to provide customized colors and surface properties.Some are naturally reflective enough to achieve cool roof standards, and surface treatments can transform tiles with low solar reflectance into cool roof tiles.
Low and Steep Sloped Roofs
Metal roofs are available with natural metallic finishes, oven-baked paint finishes, or granular coated surfaces. Unpainted metals are typically good solar reflectors but poor thermal emitters, so they rarely satisfy low slope cool roof requirements. Painting a metal roof can increase its solar reflectance and thermal emittance, allowing it to achieve cool roof status. Alternatively, you can apply cool reflective coatings.
Cost and Energy Savings
A cool roof does not necessarily cost more than a non-cool roof, especially if you are installing a new roof or replacing an existing one. However, converting a standard roof that’s in good condition into a cool roof can be expensive. Major roof costs include upfront installation (materials and labor) and ongoing maintenance (repair, recoating, and cleaning). Additional cool roof costs include specialized materials and labor. Cool roofs can save money several ways, including energy savings, rebates and incentives, HVAC equipment downsizing, and extended roof lifetime. One way to estimate how much energy you would save by installing a cool roof is by using the Cool Roof Calculator.
Climate and Environment
Your climate is an important consideration when deciding whether to install a cool roof. Cool roofs achieve the greatest cooling savings in hot climates, but can increase energy costs in colder climates due to reduced beneficial wintertime heat gains.
For Further Reading
Resources for further research into cool roofs include:
• “10 Ways to Cool Your Roof”, https://home.howstuffworks.com/home-improvement/construction/green/10-ways-cool-roof.htm