Cool Roof

A Cool Roof is a type of roofing material that reflects sunlight and is resistant to absorbing heat. Roofs that are dark in color tend to absorb heat and can become very hot in the summertime. This puts an added strain on your air conditioner and makes your energy bills go up. Most – though not all – Cool Roofs are light in color and do not absorb nearly as much heat. Roofs that are dark in color can absorb as much as 90% of solar energy and sometimes get as hot as 150 degrees F on sunny days. Cool Roofs can absorb less than 50% of solar energy, which decreases the temperature of the roof, the cooling requirement inside the house, and the money you need to spend on energy in order to cool your home.

The key factors in determining a roof's temperature are Solar Reflectance (sunlight reflected) and Thermal Emittance (heat absorbed). Solar Reflectance measures the amount of sunlight that a surface reflects. A Cool Roof will have a high solar reflectance, between 0.55 – 0.90, whereas most dark roofing material has a solar reflectance of only 0.05 – 0.20. Thermal Emittance measures how quickly a material cools by radiating heat. The higher the Thermal Emittance of a surface, the cooler it will be, even in sunny weather. The Solar Reflectance Index is calculated using a combination of a surface's Solar Reflectance and Thermal Emittance. Another factor to consider is that the Solar Reflectance of most materials will degrade over time, so when you are comparing materials based on this value, be sure to also note the 3-year Aged Solar Reflectance.

U.S. Department of Energy
ENERGY STAR
Cool Roof Rating Council

Green Roof

A Green Roof is a type of composite roofing system that includes a waterproof membrane, drainage, growing medium, and plants. There are many different ways to create Green Roofs and in most cases they are custom-designed for specific building conditions. However, as the technology becomes more developed, some companies have also developed comprehensive, modular systems that can be implemented in many different applications. These modular products are made out of interlocking units that include each of the components of the Green Roof.

There are two basic types of Green Roofs, Extensive and Intensive. Extensive Green Roofs have a relatively shallow growing medium and are the lighter and less expensive option of the two. If you are adding a Green Roof onto an existing roof structure, this may be the better option depending on the load capacity of your existing roof. Intensive Green Roofs have a deeper growing medium and can be fairly heavy and expensive to install. They also bring added benefits, such as greater thermal insulation and broader diversity of plant species that they can support.

International Green Roof Association
Green Roofs for Healthy Cities
Green Roofs Tree of Knowledge
New York City Green Roof and Landscape
U.S. Environmental Protection Agency

Materials

The roof assembly materials of your home play a critical role in protecting the inside of your home from the elements. An effective roof assembly will be made up of materials that keep moisture out and prevent unwanted heat gains and losses. The components of a comprehensive roof assembly include a roof deck, vapor retarder, insulation, and a roof covering. In some cases, a single material can play multiple roles. For example, monolithic membrane roofing materials can serve as vapor retarders and roof covering. Steep-slope roofs and low-slope roofs require different types of roof coverings. The materials that make up your roof can deflect the sun's rays, keep rain and humidity from penetrating the building envelope, and protect your home from extreme heat and cold.