Roofs do not always come to the fore when looking at ways to improve the energy efficiency of buildings. However, ‘cool roofs’, in particular, do more than simply protect a building’s occupants from natural elements.
A cool roof is one that strongly reflects sunlight and minimises the amount of heat generated when the sun heats its surface. It also cools itself by emitting radiation to its surroundings when the sun sets or weather changes. The technology means roofs stay cooler, and reduce the amount of heat conducted to the building it shelters, contributing to more stabilised internal temperatures.
Generally, light coloured materials are more likely to reflect more sunlight and absorb less energy and heat than dark coloured materials. Low thermal mass materials also emit heat quicker than high thermal mass materials.
However, there are a number of ‘cool colour’ products on the market today, whereby darker-coloured pigments which are highly reflective in the near-infrared or non-visible portion of the solar spectrum can still help to cool a building.
Here are five Australian cool roof products on the market at the moment:
Bondor’s SolarSpan is a three-in-one composite steel roofing panel that combines roof lining, high performing insulation and ceiling lining into a functional, durable and attractive product.
The roofing layer is made from hi-tensile Bluescope Colorbond steel, which makes for strength and durability in a range of thermally efficient and modern colours. The ceiling layer is also made from Bluescope Steel, and comes in two finishes.
SolarSpan’s high performing polystyrene core is what blocks the heat and keeps the roof cool. Available in a variety of thickness up to 150mm for longer panel spans and varying thermal performance, it is compliant with BCA Part J and meets regulatory requirements for minimum thermal insulation R-values in commercial roof applications.
Its high R values also allow architects to design energy efficient building envelopes.
“Because the insulating core is bonded to the steel facings, it does not crumble, sag or deteriorate over time, giving consistent insulating quality over the life of the building,” says Bondor’s general manager, Geoff Marsdon.
A service duct suitable for electrical cabling for ceiling lights and fans is further incorporated in each pane.
According to Bondor’s national product manager for Solarspan, Paul Adams, a key benefit of the product is its long span capability which, depending on application, can go up to six metres in length. This allows designers to create large, open spaces with plenty of airflow and light while reducing structural steel requirements.
Other advantages include the product’s modular design, does away with roof trusses, ceiling, insulation and roof sheets, saving a significant amount of building material and time. The insulation core also deadens noise of rain and hail.
NUTECH NXT COOL ZONE
According to Nutech Paint, a roof space can be heated up to 90 degrees Celsius on a 35 degree Celsius day in Australia, causing the temperatures of rooms below to become unbearable. While insulation helps, the firm says it will only delay the heat transfer process once heat is inside the roof space.
In response, Nutech has developed the NXT Cool Zone, a roof coating that utilises Thermal Protection Technology® to reflect heat away from the surface of the roof instead of controlling heat transfer. It was developed to reduce temperatures inside homes in hot weather.
Here, colour and aesthetics do not have to be sacrificed to reduce the heat of the roof. Instead, NXT Cool Zone can keep the surface of roofs, even darker coloured ones, up to 20 to 30 degrees Celsius cooler. This translates to a drop in temperatures from six to 10 degrees Celsius inside the home.
This is especially helpful for cases where light coloured or reflective roofs are not permitted by Council planning controls, which work to prevent glare for neighbours, and for roofs to blend into the local environment.
The standard NXT Cool Zone colours comply with Council Planning and Building Controls, which require roofs to have a Solar Reflectance Value of less than 40 per cent. It reflects between 35 and 91 per cent of the sun’s heat, although this is still subject to colour. For instance, technical information from Nutech states that NXT Cool Zone in charcoal has a total solar reflectance above 35 per cent, whereas NXT Cool Zone White has a Total Solar Reflectance (TSR) of more than 90 per cent.
Incorporating design flexibility with resource and energy efficiency, NXT Cool Zone is further enhanced with Surface Cleaning Nano Technology for water beading and self-cleaning properties. This helps to repel dirt and contamination, prevent fading of colour or loss of surface gloss, and provide waterproof protection – all of which work to increase roof product life, and ensure the roof resists ageing and deterioration.
NXT Cool Zone contains environmentally safe preservatives, and contains UV and chemical resistant non-fading pigments and tough flexible low VOC acrylic polymers.
Solacoat is a water-based acrylic coating that contains a membrane additive which reflects the sun’s solar rays, assisting in preventing heat from entering a building or home.
The percentage of rejected solar rays varies depending on the actual colour being applied, as well as whether the newly coated roof is corrugated, flat or pitched. Solacoat Dark Colours provide less solar reflectivity than the Pastel Colours range, with White having a TSR of 80 per cent, Ivory Porcelain a TSR of 70 per cent, and terracotta a TSR of 41 per cent.
Testing has shown that in summer, Solacoat Cream can reduce the temperature of a newly coated metal roofing by up to 30 degrees Celsius.
The coatings not only assist in preventing buildings from heating up, it also inhibits rust, corrosion and thermal expansion, ensuring durability. It is non-toxic and contains anti-fungal and anti-mould properties.
Easy to apply, it requires one 50 micron thickness wet or Primer, and two 50 micron thickness wet topcoat applied to the surface. According to Coolshield, Solacoat will keep performing for a minimum of ten years.
It is certified by ASTM International Standards, and compliant with NATA and APAS standards.
COLORBOND COOLMAX STEEL
Taking into account the fact that energy costs are only going up and not down, Colorbond Coolmax is a pre-painted steel roofing with a high solar reflectance, developed with the principal intent of maximising the Total Solar Reflectance (TSR) that could be achieved for a durable Colorbond steel finish.
According to BlueScope product development portfolio leader, Detlev Mueller, the most recent physical development of Coolmax steel is its upgrade to using the recently launched, next generation ZINACLUME steel with Activate™ technology. This has enhanced the corrosion performance of the Coolmax steel roof, while leaving the product’s TSR unaffected.
The product is currently only available in Whitehaven™, which has a nominal solar reflectance of 0.77, and affords the best practical TSR results.
“Not only is the colour Whitehaven™ more reflective than the colour Surfmist® by virtue of its pigmentation, COLORBOND Coolmax steel also utilises a unique primer formulation that is optimised for solar reflectance,” says Mueller.
“The total coating package is applied at a greater thickness than standard Colorbond steel to optimise solar reflectance without compromising any of the other critical attributes expected of Colorbond steel products.”
According to independent roof studies by the US Environmental Protection Agency, Colorbond Coolmax steel roofs in Whitehaven have nine per cent higher solar reflectance than Colorbond Steel roofs in Surfmist. This contributes to lower internal temperatures, which allows the Coolmax roofs to reduce the annual cooling costs of buildings by up to 7.5 per cent.
Coolmax steel roofs also have all the qualities of typical Colorbond steel, such as excellent resistance to dirt retention, and the maintenance of solar reflectance. For example, a 2005 BlueScope Steel research showed that samples of Colorbond steel in Surfmist, which were exposed for over a decade at the BlueScope Steel testing facility in Queensland, retained 95 per cent of their initial solar reflectance.
These advantages mean that a Colorbond Coolmax roof can reduce the peak cooling load of a building, which in turn minimises the need for air conditioning equipment. This helps to save capital costs on cooling equipment and running costs, whilst mitigating the impact of Urban Heat Islands (UHI).
Mueller adds that further developments are underway relating to the ways in which Colorbond Coolmax steel can contribute to improved performance of built structures. One example is the work currently undertaken as part of the Urban Micro Climates research Project for Sydney, Melbourne and Adelaide with the Low Carbon Living CRC.
DULUX ACRATEX INFRACOOL
Dulux’ InfraCOOL technology is an option for most colours across the Dulux AcraTex Roof Membrane colour range, and uses specific pigments that target and reflect the sun’s invisible infrared radiation.
According to Dulux, Acratex InfraCool offers three times the TSR of a standard weathered galvanised roof surface, which absorbs large amounts of solar radiation and transmit heat into occupancy zones.
The product was therefore designed as a barrier to combat the light energy before it is absorbed as heat in the roofs, maximising insulation and cooling efficiencies.
By bouncing back radiant heat, roofs treated with InfraCool can be 20 to 40 degrees cooler. For instance, a standard charcoal roofing has a TSR of just 6.8 per cent, but with InfraCool, this jumps up to 26.9 per cent.
For non-air conditioned facilities, such as workshops and warehousing, this can translate to cooler working conditions.
In the case of conditioned facilities, applying InfraCool to the roofs can also improve productivity and reduce power consumption, thus contributing to lower running costs and carbon footprint.