A cool roof reflects and emits the sun's energy as light back to the sky instead of allowing it to enter the building below as heat.
In many climate zones, a cool roof can substantially reduce the cooling load of the building, providing several direct benefits to the building owner and occupants:
increased occupant comfort, especially during hot summer months
reduced air conditioning use, resulting in energy savings typically of 10-30%
decreased roof maintenance costs due to longer roof life
reduced peak demand for electricity, helping to lower costs and avoid power outages
A cool roof need not be white. There are many "cool color" products which use darker-colored pigments that are highly reflective. With "cool color" technologies there are roofs that come in a wide variety of colors and still maintain a high solar reflectance.
Built-up Roofing (includes asphalt and coal tar pitch): Built-up Roofing (BUR) consists of built-up layers of asphalt and plies that can be covered with a capsheet (or surfacing material). The "cool" products found in this category refer to the properties of the capsheet.
Metal: Metal roofs 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.
Single-Ply: Single-ply roofing is a pre-fabricated sheet of rubber polymers that 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.
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 weather exposure and can be found in their rated products directory.