According to the Australian Department of the Environment, homes Down Under are directly responsible for almost a fifth of the country’s greenhouse gases. Their studies show that the average home produces over 7 tonnes of emissions. Heating and cooling systems contribute most (40%) to this figure.

1. The Design Principles
That Make Cool Roofs
Energy-Efficient
Permacoat
Ph: (08) 9249 5955
Address: 90 Beringarra Ave, Malaga, WA 6090

2. According to the Australian Department of the Environment, homes Down Under are
directly responsible for almost a fifth of the country’s greenhouse gases. Their studies
show that the average home produces over 7 tonnes of emissions. Heating and cooling
systems contribute most (40%) to this figure.
Because the dramatic increase in electricity consumption produces such a significant
environmental impact, the government has started advocating the use of energy-
efficient technologies and observation of energy-conservation efforts.
One excellent example of a cost-effective way to reduce energy use and carbon
footprint is the use of cool roofs. Studies have shown that roof restoration and
installation of these protective structures reduce the amount of heat entering the
space, which decreases the need for operating HVAC systems and thus leads to a
reduction in energy consumption.

3. This energy-saving benefit from cool roofs
is possible due to its design, which
operates in two principles: solar
reflectance and thermal emittance.
Solar Reflectance
Solar reflectance is the ability of a
material to reflect solar energy from its
surface back into the atmosphere. It
involves a range of wavelengths, including
ultraviolet, visible and infrared light.
The colour of the roof reveals a great
deal about its solar reflectance; the
general principle is the lighter the roof
colour, the greater its reflectivity.
Traditional dark-coloured materials often
have a solar reflectance of approximately
0.04 to 0.18, while light-coloured ones
have0.70 or higher. Dark-coloured
roofing, however, can have greater solar
reflectance with the use of special
coating, called cool colour technologies.

4. Thermal Emittance
Roofing materials cannot completely reflect heat, as they retain solar energy. Some of
the absorbed heat should then be emitted back to the environment through infrared
radiation.
Thermal emittance is the relationship between the amount of emittance a specific surface
can produce and the amount of emittance a perfect blackbody can at the same
temperature. The values for this range from 0 to 1, with low emittance roofs becoming
hotter than the high emittance roof.
Most roofing materials have a thermal emittance of 0.80, but those that are made of
metals have lower values, approximately between 0.20 and 0.60, depending on the
surface conditions.
Cool roofs have higher solar reflectivity and higher thermal emittance than traditional
roofs. These properties make the roof surface reach temperatures as low as -1°C - 15°C,
which reduces over-all heat gain and the house’s cooling requirements.
The increased energy use in Australian households presents the need for the use of
energy-efficient technologies, such as cool roofs. With higher solar reflectance and
thermal emittance, homeowners can save more money and minimise environmental
impact with reduced energy consumption.
RESOURCES:
http://www.permacoat.com.au/roof-restoration/
http://www.environment.gov.au/resource/help-prevent-climate-change
http://www.yourhome.gov.au/energy/heating-and-cooling
http://yourenergysavings.gov.au/energy/heating-cooling/understand-heating-cooling