Roofs are one of the major interfaces between buildings and the
atmosphere. Solar energy absorbed by a roof is transferred either
into the building below or to the atmosphere above. Roofs have
been traditionally dark in color, thus absorbing a large fraction
of incoming sunlight. However, roofs can also be made of highly
reflective materials that stay cooler in the sun.
Past monitoring studies have found that increasing the solar
reflectance (fraction of incident solar energy that is reflected) of
a roof to 0.60 from about 0.10–0.20 can decrease cooling energy
use by 10–20% or more [1–7]. Cooling energy savings can vary with
building construction, roof insulation, shade cover, and climate.
Widespread use of reflective roofs in urban areas can lower air temperatures,
helping mitigate the urban heat island effect [8–11], and
improve air quality [2,8,9]. Installation of reflective roofs and pavements
has also been proposed as a method to counter the climate
warming effects of greenhouse gases [12–14].
Roofs can also be used to site photovoltaic (PV) modules that
convert a modest fraction of incoming sunlight to electricity. Crystalline
silicon modules account for approximately 85–90%