Los Angeles Cool Roof Technology
What is a Cool Roof?
Cool roofs are designed to reflect more sunlight and absorb less heat than standard roofs. They can be made of highly reflective tiles/shingles, reflective paint, or a sheet covering. In comparison, under the same conditions, cool roofs could stay more than 50°F cooler than standard or dark roofs as those can reach temperatures of 150°F or more in the summer sun, especially in California.
By reducing the amount of heat that’s absorbed, you can save energy and money by using less air conditioning. Pretty much any building can benefit from a cool roof but other factors such as climate should be taken into consideration before installing one.
Benefits of Cool Roofs
Decreasing air conditioning needs reduces energy bills.
Not all spaces in a home or building has air conditioning such as garages or covered patios. Cool roofs can improve indoor comfort for those spaces.
Decreased roof temperatures may extend the overall roof service life.
According to the U.S. Department of Energy, cool roofs can also benefit the environment, especially when man 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.
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
With the various types of roof systems available, the surface exposed to the sun is the one that determines if a roof is cool or not. These days, we have the ability to select the appropriate surface to make a new or existing roof cool.
Cool roof coatings are white or special reflective pigments that reflect sunlight. Like very thick paints, coatings can protect the roof surface from ultra-violet (UV) light and chemical damage. They also offer some water protection and restorative features.
Low Sloped Roofs
Single-ply membranes are prefabricated sheets rolled onto the roof and attached with mechanical fasteners, adhered with chemical adhesives, or held in place with ballast (gravel, stones, or pavers).
How they can be made cool: Reformulate or coat black membranes to make them reflective.
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
Modified bitumen sheet membranes have one or more layers of plastic or rubber material with reinforcing fabrics, and are surfaced with mineral granules or a smooth finish. These can also be used to surface a built-up roof—known as a “hybrid” roof.
How they can be made cool: Pre-coat with a cool roof coating at the factory.
Spray polyurethane foam roofs are constructed by mixing two liquid chemicals together that react and expand to form one solid piece that adheres to the roof. Foams are highly susceptible to mechanical, moisture, and UV damage, and reply on a protective coating.
How they can be made cool: The protective coatings are usually already reflective, and offer cool roof performance.
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.
How they can be made cool: 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 finished, or granular coated surfaces.
How they can be made cool: 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.
You may also consider installing a green roof. Green roofs are ideal for urban buildings with flat or shallow-pit roofs, and can include anything from basic plant cover to a garden. The primary reasons for using this type of roof include managing storm water and enjoying a rooftop open space.
Green roofs also provide insulation, lower the need for heating and cooling, and can reduce the urban heat island effect. This roof type can be much more expensive to implement than other efficient roof options, so you should carefully assess your property and consult a professional before deciding to install a green roof.
Deciding Whether to Install a Cool Roof
When deciding whether to install a cool roof, you’ll need to determine whether the cost will justify the energy savings. How much energy you will save depends on several factors such as your home’s climate and environment, how well insulated your current roof is, the type of roof you have, and the efficiency of your heating and cooling system
If you are building a new home, you can decide during the planning phase what type of roof to install and whether it should be a cool roof. If you want to convert an existing roof into a cool roof, you have three basic options:
Retrofit the roof with specialized heat-reflective material
Re-cover the roof with a new waterproofing surface (such as tile coating)
Replace the roof with a cool one
If your roof is in poor condition or near the end of its life, it is usually best to re-cover, replace, or retrofit the roof.
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.
In warm, moist locations, cool roof surfaces can be more susceptible to algae or mold growth than hot roofs. Some roof coatings include special chemicals that prevent mold or algae growth for a few years.
In cold climates, roofs can accumulate moisture through condensation, and it is possible that cool roofs might be more susceptible to accumulating moisture than dark roofs of the same design. Condensation can be avoided using proper design techniques.
Information Retrieved from the U.S. Department of Energy.