Cool Roofing Information for Home and Building Owners
What is a Cool Roof?
A cool roof is one that strongly reflects sunlight and also cools itself by efficiently emitting radiation to its surroundings. The roof literally stays cooler and reduces the amount of heat conducted to the building below. If a building does not have air conditioning, this keeps the building cooler and a more constant temperature. If a building has air conditioning, the equipment does not have to work as hard. Imagine wearing a white or a black T-shirt on a hot day. By wearing the white T-shirt you will remain cooler than if you wore a black T-shirt because it reflects more sunlight and absorbs less heat. Cool roofs, like a white T-shirt, keep the internal temperature of the building lower.
However, a cool roof need not be white. There are many "cool color" products which use darker-colored pigments that are highly reflective in the near infrared (non-visible) portion of the solar spectrum. Because a white roof strongly reflects both visible and near infrared sunlight, a white roof will typically be cooler than a cool colored roof.
The two basic characteristics that determine the "coolness" of a roof are solar reflectance (SR) and thermal emittance (TE). Both properties are rated on a scale from 0 to 1, where 1 is the most reflective or emissive.
The CRRC measures these two properties for roofing products, both for the product's initial values and after three years of outdoor exposure. The CRRC publishes the results on the online Rated Products Directory. The online Directory is available to the general public at no charge, and it allows you to compare the rated values of various product types and brands.
What are the Benefits of a Cool Roof?
A cool roof can significantly reduce your cooling energy costs and increase your comfort level by reducing temperature fluctuations inside your home. Average energy savings range from 7%-15% of total cooling costs. Some other benefits include:
- Reducing your utility bills associated with air conditioning
- Increasing occupant comfort and avoiding installation of an air conditioner where there isn't already one
- Decreasing the size and prolonging the life of your air conditioning system
- Lowering roof maintenance costs and extending roof life, avoiding reroofing costs and reducing solid waste
- Assisting your home in meeting building codes
- Mitigating your community's Urban Heat Island Effect
- Maintaining aesthetics with a roof that performs and looks good
- Receiving utility rebates (in some locations)
- Indirect benefits
What is the Right Roofing Material for Your Home or Building?
Although the CRRC cannot recommend specific roofing products, below is a description of some things to consider in selecting a roofing product for your building, including a description of the types of roofing materials currently rated in our program.
All roofs essentially fall into one of two general categories: low-slope (less than 2 inches of rise over 12 inches of run) and steep-slope (2:12 or greater). Our directory indicates which slope(s) a product is intended for. We recommend that you check with a local roofing contractor, roof consultant or architect to determine the most appropriate roofing product type for your home.
In most climate zones worldwide, cool roofs can significantly reduce a building's cooling load. However, cool roofs can also increase heating costs in winter months. This increase is usually greatly outweighed by the cooling energy savings achieved during summer months because the sun is low in the sky during winter months, the weather tends to be overcast, and snow often covers the roof, usually making the heat gain through the roof negligible in all but the most northern climate zones in the US.
In selecting your roof, it is important to understand your climate zone and the actual energy your home or building will save. There are two cool roof calculators available online that can give good estimates of how much energy you will save. You can find them at:
Below is a list of definitions of roof product types. To Search the CRRC Rated Products Directory, click here.
Built-up Roofing (includes asphalt and coal tar pitch): Built-up Roofing (BUR) consists of built-up layers of coated asphalt and insulation applied on site and can be covered with a capsheet (or surfacing material). The "cool" products found on the CRRC Rated Products Directory in this category refer to the properties of the capsheet.
Foam Roof Systems: Foam systems can also be divided into the field-applied and factory-applied categories. Field-applied foam systems are similar to field-applied coatings, as they are sprayed on in liquid form and harden as they set on top of the roof. Factory-applied foam systems are formed into rigid panels and coated with a reflective coating. The foam usually gives the roof system additional insulation properties.
Metal: Metal roofing products can be shaped to look like shingles, or shakes, or to fit unique curvatures, in addition to a typical standing seam configuration. They come in a variety of textures and colors, including some darker "cool" colors with special additives that allow these dark colors to achieve significantly greater reflectance than previous versions of the same product.
Modified Bitumen: Modified bitumen is bitumen (asphalt or tar) modified with plastic and layered with reinforcing materials then topped with a surfacing material. Like BURs, the radiative properties of modified bitumen (mod bit for short) are determined by the surfacing material.
Roof Coatings: Roof coatings can be divided into two categories: field-applied and factory-applied. Field-applied coatings are applied directly onto the roof surface, either on a new roof assembly or over an existing roof surface (and can be applied over top of just about anything, so long as the right coating is selected). Factory-applied coatings are applied at the factory prior to distribution. Examples of factory-applied coatings include coatings applied to metal and glazes that are applied to tiles.
Shingles, Slate, or Tile: All of these products types use the same concept, where pieces fit together to form a roof. Asphalt shingles are fairly common for residential roofing applications, probably because they are relatively inexpensive and simple to install. Slate and tile products also come in a wide variety of colors, shapes and textures, and, because of their heavy mass, they have thermal properties that may yield additional energy savings beyond their reflectance and emittance properties.
Single-Ply: Single-ply roofing is a pre-fabricated sheet of rubber polymers. Single-ply roofing is laid down in a single layer over a low or steep-sloped roof. The single-ply membrane can be loose-laid and weighted down with ballast or pavers or firmly set on the roof and attached with mechanical fasteners or adhesives. There are two main types of single-ply materials:
- Single-Ply Thermoset (includes EPDM, Hypalon): Thermosets are materials that can not be hot-air welded because it changes their physical characteristics. Instead, tape or a contact cement to seal the seams.
- Single-Ply Thermoplastic (includes TPO, PVC, etc.): Single-Ply Thermoplastic is a flexible sheet membrane which consists of compounded plastic polymers. When heat is applied onto the surface, the single-ply thermoplastic seams are melded together making the material seamless and effective. Most thermoplastics are manufactured to include a reinforcement layer (usually polyester or fiberglass) for extra durability and strength. There are various types of single-ply thermoplastic such as PVC & TPO. PVC (polyvinyl chloride) is a synthetic polymer prepared from vinyl chloride. It tends to be more expensive than TPO, but is well known for long-term performance and is naturally fire-retardant. TPO (thermoplastic polyolefin) is a blend of polymers that can contain flame-retardants or UV absorbers.
Other: This is where the CRRC places any product that does not fit anywhere else. For example, we have a roof surfacing system, a rubber membrane, stucco, roll roofing and a few others.
Product Types Currently Not Included in the CRRC Rating Program:
Ballasted Roofs: Ballasted roofs are roofing systems that include a waterproof material (like a single-ply membrane) weighed down with heavy materials, called a ballast. The ballast is typically some sort of stone or concrete paver.
Green Roofs: Green roofs (also known as garden roofs or vegetated roofs) use plants as roof covering. Though typically not highly reflective, green roofs can stay cool by evaporating water. They can also reduce storm water runoff. Green roofs are distinct from cool roofs and are not rated by the CRRC.
Here are some links to online directories that assist homeowners with locating a contractor within their area.
Determining if You Qualify for a Cool Roof Rebate
Different locations across the country provide rebates for installing cool roofs. See if your area offers a rebate! The CRRC's list of rebate programs is not exhaustive, so please also check with your local utility company.