Click one of the letters above to advance the page to terms beginning with that letter.



The ratio of reflected to incident sunlight, measured on a scale of 0 to 1 (or 0-100%), where higher numbers indicate greater reflectance. Also known as "solar reflectance."

Asphalt shingles

Typically fiberglass sheets soaked with asphalt for waterproofing and covered with granules (crushed rock, often colored) to shield the asphalt from ultraviolet light. It is one of the most widely used residential roofing materials in the U.S.



A heavy roofing material, typically a stone or concrete paver, used to weigh down waterproof layers (e.g. a single-ply membrane) and increase the thermal mass of the surface to decrease heat flux through the roof.


Car shell

The opaque elements of the car’s envelope, such as its roof and doors.


The molecular transfer of heat, such as the flow of heat through a solid.


The transfer of heat by circulation or movement of a fluid (liquid or gas).

Cool roof

A roof that stays cool in the sun by reflecting sunlight (to minimize solar absorption) and emitting thermal radiation (to help dissipate solar heat gain).


A cool-colored material strongly reflects the invisible “near-infrared” radiation that makes up nearly half of sunlight. Replacing a standard (warm) color with a matching cool color can boost solar reflectance by as much as 0.4 without affecting appearance. (We note that a light color, such as white, is also cool, but the term “cool color” is most commonly used to describe a surface that reflects more strongly in the near-infrared spectrum than in the visible spectrum.)


Elastomeric coating

A liquid surfacing material (acrylic, elastomeric, or asphaltic) for various roof types, especially built-up roofing (BUR) and metal. Available in different colors; may be divided on the basis of reflectivity into black, aluminum, white, and tinted coatings.


Fuel economy

The ratio of distance traveled to fuel consumed, typically expressed in miles per gallon or kilometers per liter.


Green roof

A roof that is partially or completely covered with vegetation and a growing medium (e.g., soil), planted over a waterproofing membrane. Also known as “living roofs,” "roof gardens," or "vegatative roofs," this type of roof serves to absorb rainwater, provide insulation, create a habitat for wildlife, and help to lower urban air temperatures and combat the heat island effect through evapotranspiration.


Heat transfer

The flow of heat from a warmer region to a cooler region.



The geographic coordinate represented by lines running from east to west that are parallel to the equator.


The geographic coordinate represented by lines running from north to south. The line passing through the Royal Observatory, Greenwich in England is defined as zero degrees of longitude, or the Prime Meridian.

Low-slope roof

A roof with a pitch less than or equal to 9.5° (2:12).



The portion of the solar spectrum that spans wavelengths from 700 to 2500 nm; longer in wavelength than both ultraviolet and visible light. Also sometimes called solar infrared.


Painted metal

A roofing product made of metal (bare or factory coated). Available in many shapes.


The number of layers of roofing (e.g., one-ply, two-ply), typically used to characterize membrane roof coatings.


Single-ply membrane

A roofing material that consists of one layer of membrane material rather than multiple layers. It is rolled onto the roof and attached with mechanical fasteners, adhered with chemical adhesives, or held in place with ballast (gravel, stones, or pavers).


The degree of roof incline expressed as the ratio of rise to run (e.g., 2:12), or as an angle from horizontal (e.g., 9.5°).


A type of air pollution containing ozone and other reactive chemical compounds formed by the reaction of sunlight with hydrocarbons and nitrogen oxides. Derived from the combination of "smoke" and "fog."

Solar reflectance

The ratio of reflected to incident sunlight, measured on a scale of 0 to 1 (or 0-100%), where higher numbers indicate greater reflectance. Also known as "albedo."

Solar reflectance index

A metric for comparing the coolness of roof surfaces. The higher the SRI, the cooler the roof will be in the sun. For example, a clean black roof has an SRI of 0, while a clean white roof has an SRI of 100. Many building codes and utility rebates now specify minimum values of SRI.

Solar spectrum

The spectral distribution of radiative energy in sunlight. At the earth's surface, about 99% of sunlight arrives in at wavelengths between 300 and 2500 nm.

Steep-slope roof

A roof with a pitch exceeding 2:12 (9.5°). Better described as a high-slope roof (contrast low-slope roof), steep roof, or pitched roof, but the term “steep-slope” is embedded in the roofing industry and in building codes.


Electromagnetic radiation from the sun (see solar spectrum).


Thermal emittance

The efficiency with which a surface cools itself by emitting thermal radiation, measured on a scale from 0 to 1 (or 0–100%), where a value of 1 indicates perfect emission (i.e., equal to that of a black body cavity).

Thermal radiation

Electromagnetic radiation emitted from a surface. The spectrum of this radiation depends on the temperature of the surface. "Thermal" radiation typically refers to that emitted by a surface whose temperature is near 300K (~25°C).

Tile roof

A roof made of concrete, clay or slate tiles.



The portion of the solar spectrum that spans approximately 300 - 400 nm; shorter in wavelength than visible and near-infrared light, and cannot be seen.

Urban heat island

A regional elevation in air temperature, usually gauged by the difference between urban and rural air temperatures. This website focuses on the summer afternoon urban heat island effect.



The portion of the solar spectrum that spans approximately 400 - 700 nm; longer in wavelength than ultraviolet light and shorter than near-infrared, it is the only portion of the spectrum that humans can see.