In a pre-engineered steel building system, a cool roof refers to the colour of the metal roof cladding. Using a cool white, or other light colours, has numerous positive effects on the building and the surrounding environment.
A cool coloured roof provides a much higher solar reflectance and a higher thermal emittance than other dark colours or galvanized steel. Solar reflectance refers to the colours reflection of infrared, ultraviolet and visible wavelengths of the sun. Thermal emittance refers to the colours absorptive abilities of solar energy. Both these values are measured between 0 and 1; the higher the value, the higher the roof ability to reflect the sun’s heat.
The effects of urban development have been observed in a phenomenon call “urban heat island”. This occurs in a developed area that experiences higher temperatures than its surrounding area, especially at night. This is caused by buildings retaining heat during the day, as well as waste heat expelled by buildings mechanical systems. This rise in temperature has numerous harmful effects on the environment including altering wind patterns, rain fall, development of clouds and thunderstorm activity as well as peoples health. All this impacts the cities weather as well as surrounding ocean and rural areas. And almost 90% of the roofs in North America are dark in colour.
The Benefits of a cool roof on a metal building are:
- Slower deterioration of metal cladding on the roof. As the sun is almost entirely reflected, the harmful effects the sun can have on a roof are alleviated.
- Having a cool roof provides credit towards Leeds certification – specifically Sustainable sites credit 7.2
- In the pacific north-west, a cool coloured roof limits the need to cool a pre-engineered steel building during the day by 15-25%. Even if it isn’t hot but is bright, a cool coloured roof will help with keep the buildings temperature optimal. Also lower heat gain increases the efficiency of the roof insulation in either cooling or heating.
- Reduces air pollution by reducing mechanical systems operation time.
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