Low Energy House Design Principles: Cool Roofs


 Read on to find out how a 'cool roof' can help save on your energy bills and how they can improve our environment.

What is a Cool Roof?

Most people’s roofs are dark-coloured, causing the temperature of the surface to increase by more than 37 degrees over the surrounding air temperature. A cool roof solves this problem, delivering higher solar reflectance and higher thermal emittance than traditional roofs. Solar reflectance refers to the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to the building. Thermal emittance refers to the ability to radiate absorbed or non-reflected solar energy. Previously, cool roofs have been either white or some other lighter shade. Now, with new technology and the development of residential cool roof products, high solar reflectivity can be achieved using even dark, rich hues. Cool roofs can also improve roof durability and reduce both building cooling loads and the urban heat island effect.

Types of Cool Roofs

There are three types of cool roofs - roofs made from cool roofing materials, roofs made of materials that have been coated with a solar reflective coating, or green roofs.

Cool Roofs

White thermoplastic membrane roofs can achieve some of the highest reflective and emittance measurements of which roofing materials are capable of. A roof made of white thermoplastic can reflect 80% or more of the sun’s rays and emit at least 70% of the solar radiation absorbed. Whereas, an asphalt roof can only reflect between 6 and 26% of solar radiation. However, high consumer demands for darker colours which still reflect sunlight, is causing different materials, coating processes and pigments to be investigated for use in cool roofs.

Coated Roofs

Coated roofs refer to an existing roof that has been made reflective by applying a solar reflective coating to its surface.

Green roofs

As mentioned in the article ‘Low Energy House Design Principles – Green Roofs’, green roofs have a thermal mass layer that helps reduce the amount of heat absorbed by a building and can soak up the sun’s radiation without emitting it back to the world as heat, which also make them a lot better for the environment. They may not reflect as much as traditional cool roofs, but they have other benefits like absorbing rainwater, providing natural insulation and lowering urban air temperatures.

What are the Benefits of a Cool Roof?

Installing a cool roof can benefit you in many ways. Their main advantages include:

·         A reduce in energy use as less heat is transferred to the building below, lessening the need for air conditioning and thus, lowering your utility bills

·         An increase in your overall health and indoor comfort by preventing heat related illnesses

·         Reduced air pollution and greenhouse gas emissions by reducing the ‘urban heat island effect’

·         Improved roof durability and less roof maintenance costs

·         Lessens the electricity demand during peak hours (generally experienced in summer late afternoons as businesses and residences turn up their air conditioners), thus lessening the burden on the power grid