Smart Roof for Green Building in Small City

Abstract

A cool roof is defined as the one that reflects the sun’s heat and emits absorbed radiation back
into the atmosphere. The roof thus, remains cooler and reduces the amount of heat in the
building. It is well known that light colored reflective surfaces heat up less in the sun. Cool roof
may be white, but it need not necessarily be white as there are cool colours available which use
dark coloured pigments and still are highly reflective. Cool roof can be compared with white
shirt; normally one prefers to wear the same reason during summer. Cool roofs reflect more
sun lights and absorb less heat than traditional dark-coloured roofs but most of the roofs in the
world are dark-coloured. In the heat of the full sun, the surface of the black roof can increase
the temperature as much as 50 degree centigrade. Cool roof provides through solar reflectance
surfaces which are comparatively cool and thus provides comfortable conditions inside the houses.
The advantage of cool roof, properties and cool roof based on the solar reflectance and thermal
eminence and describes essential materials for a green roof construction. The paper discusses
the importance of green roof in Bangalore city to control the temperature increase. It suggest
roof garden as one of the solution to deal with the heat island phenomenon to fight the urban
heat island effect.The most important feature of an ideal cool roof is that its surface strongly
reflects sunlight. The surface of an ideal cool roof should also efficiently cool itself by emitting
thermal radiation. Thus, a cool roof should have both high “solar reflectance” (ability to reflect
sunlight, measured on a scale of 0 to 1) and high “thermal emittance” (ability to emit thermal
radiation, also measured on a scale of 0 to 1). The solar reflectance and thermal emittance of a
surface are called its “radiative” properties because they describe its abilities to reflect solar
radiation and emit thermal radiation. For cool roof design parameters like solar reflectance
index (SRI) and thermal emittance are defined and the values are obtained for cement, paint
and other materials. Based on the discussion it is recommended to have high values of SRI to
construct a cool roof in Bangalore.