The ancient Greeks were ahead of their time in painting their homes and roofs white to reflect the sun’s rays. Today the ‘cool roof’ concept uses similar yet more advanced technology on modern homes and other buildings to help reduce energy use by creating solar reflective surfaces.
Though they both reduce heat absorption, a cool roof differs from a green or living roof in that it uses specific reflective treatments or surfaces rather than vegetation to achieve this result.
A standard roof can reach temperatures well over 100 degrees in the height of summer. A cool roof under the same conditions can be more than 50 degrees cooler by simply reflecting the sun.
There are significant benefits of a cool roof:
- Reduced energy bills by decreasing the need to use air conditioning
- Improved indoor comfort for spaces that are not air conditioned
- Decreased roof temperature, which may extend the life of the roof
Cool roofs can also positively impact the environment, especially when a number of buildings within a community utilize them. When this is the case, cool roofs can;
- Reduce local air temperatures often referred to as the urban heat island effect
- Lower peak electricity demand, which can help prevent power outages
- Reduce power plant emissions, including carbon, nitrous and sulfur dioxides and mercury, by decreasing building energy use
There are a wide variety of cool roof products that can be used for new or existing roofs.
Cool roof coatings
White or special reflective pigments that redirect rather than absorbing sunlight. These coatings are similar to thick paints that protect the roof surface from ultra-violet (UV) light and chemical damage. Some also provide water protection. These coating products are available for most roof types.
Cool asphalt shingles
These shingles use specifically coated granules that provide increased solar reflectance. Other roof shingles can be coated at the factory or in the field to make them more reflective. Coating existing asphalt shingles to make them cool is not generally recommended or approved by shingle manufacturers and may void the warranty and limit the life of your roof.
Comprised of clay, concrete or slate, some tiles already possess inherent reflective properties. They can also be glazed or coated to transform them into cool roof tiles. As an added bonus, these coatings can also increase water resistance and they come in a variety of light, reflective hues.
Making a Roof Cool:
Just about any roof can be made into a cool roof. Low sloped or flat roofs can be made cool by replacing or coating the waterproof membranes and replacing dark gravel with reflective options. For roofs with an asphalt emulsion coat, a cool version can be applied to transform it to a reflective surface. Metals roofs are reflective if unpainted or a variety of cool surface treatments can also be applied.
Taking The Plunge: Should You Go Cool?
When making the decision whether to install a cool roof, you first need to determine if the cost justifies the energy savings.
How much energy you will save depends on several factors:
- Your home’s climate and environment
- How well your current roof is insulated
- The type of roof
- The efficiency of your HVAC system
If you are building a new home, you can make the decision during the planning phase whether it pays to install a cool roof. One way to estimate how much energy you would save by installing a cool roof is by using a cool roof calculator.
If you’d like to modify an existing roof into a cool variety, you have three basic options:
- Coat the roof
- Recover it with a new waterproofing surface
- Replace it
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.
The Cost of a Cool Roof
A cool roof costs about the same as a standard roof, especially if you are installing a new roof or replacing an existing one. However, converting a standard roof that is 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 as well as possibly extending the lifetime of your roof. 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 also decrease energy costs in colder climates due to reduced beneficial wintertime heat gains.