A recently completed warehouse and office in Philippi, Cape Town, is clad with multi-coloured pre-painted steel panels and has a high solar reflective index roof to minimise inbound infrared radiation. Popular roofing material, Clean COLORBOND™ steel with Thermatech™ solar reflectance technology coating, was recently used in the construction of this high tech new warehouse for client, Holdsport Ltd.
The Solar Reflectance Index (SRI) is widely used by green building rating tools to mitigate the Urban Heat Island (UHI) effect. SRI is a value that incorporates both solar reflectance and thermal emittance in a single value to represent a material’s temperature in the sun. SRI quantifies how hot a surface would get relative to standard black and standard white surfaces.
Cape-based architects for the building, Bam Architecture, advised that design approval meant SANS 10400 part XA compliance for the office portion of the building. Accordingly, the energy efficient building utilises high performance glazing and cavity insulation in certain walls, as well as under the concrete roof slab. 75mm Factorylite insulation was used under the roof. To support optimal thermal performance, the building is clad and roofed using premium brand pre-painted aluminium-zinc material, Clean COLORBOND™ steel to specification AZ150.
The sparkling white roof was built using Global Roofing’s Kliplok 406 profile made from Clean COLORBOND™ steel in colour African White (TCT 0.53mm) with SRI value of 85. The walls sport an IBR686 wall cladding of the same steel (TCT 0.47 mm) in colours African White, Armour Grey and Shale Grey. Roofing and cl adding was by Chartwell Roofing. According to Bam Architects, the choice of 3 colours was an aesthetic one, but the raised curved profiles in the sidewalls (see photograph) are walled with tranlucent sheeting in the return sections, which allow a degree of natural light to enter the warehouse.
BlueScope’s General Manager, Wayne Miller, explains that Clean COLORBOND™ steel with Thermatech™ technology was recommended due to its extraordinary performance especially in hot climates and along the coastal zone.
Energy efficiency inside a building envelop may be attained in various ways, including:
– Light coloured roofing materials to reduce solar heat gain
– The use of low thermal mass materials that respond to temperature changes comparatively quickly in contrast with high thermal mass materials that take longer to heat or cool
– Insulating the walls, ceilings, roofs and suspended floors
– Favourably orientating the building and providing exterior shading to control solar heating and wind flow
– Thermatech™ solar reflectance technology <end bullets & sidebar item>
In hot tropical climates, low thermal mass materials such as steel with light coloured roofs and walls can be used to reduce energy demand for internal cooling. For example, a light coloured Clean COLORBOND™ steel roof not only reduces the amount of solar radiation absorbed, but is also very effective at re-radiating heat. Such thermal comfort is maintained by the dirt resistance property in Clean COLORBOND™ steel. Since the addition of Thermatech™ solar reflectance technology, even darker coloured Clean COLORBOND™ steel products absorb now less energy, creating the advantages of a cooler roof and a cooler building, similar to lighter shaded colours.
According to Wayne Miller, the solar reflectance technology lowers the surface temperature by absorbing less heat from the sun. “Thermatech™ optimises the thermal performance of every colour in the standard Clean COLORBOND™ steel and Clean COLORBOND™ Ultra steel palettes, without changing their appearance. This provides greater thermal comfort all year round whilst using less energy for air-conditioning and hence mitigating the UHI effect” he says. “In addition our product’s outstanding dirt resistance property ensures the roof looks newer for longer. This also assists in cooling.”
In a comparison between a Clean COLORBONDTM and a conventional steel roof, both uninsulated, the positive effect of dirt resistance technology is illustrated. Tests show that after two years’ exposure, assuming an irradiance of 1000W/m², exterior temperature of 36°C and a high thermal emittance value of 0.85, typical of pre-painted steels, the Clean COLORBONDTM steel roof’s temperature is almost 10° cooler than the conventional steel roof and it radiates more than 40W/m² less heat down into the building.
Emergency life safety system water supply
Made from ZINCALUME® steel, a pair of circular tanks in the yard of capacity 414 000 kl each supply high pressure water for the automatic sprinkler system used for fire fighting inside the warehouse. Specified by Aurecon as an integral part of the building’s life safety and fire fighting systems, the tanks are model ST12/08 built by SBS Water Systems in Durban. As far as light weighted durability, ZINCALUME® steel tanks are in a class of their own. According to Brian Wilson, Sales and Marketing Manager for the supplier, “SBS™ has been installing tanks made from ZINCALUME® in South Africa and beyond since 1998 and chooses to use only ZINCALUME® steel as the material used in the manufacture of the outer shell and roof cover of our SBS Tanks™ range because of its proven track record as a superior product with excellent strength and corrosion resistant properties and the consistent quality of the material we receive.”
“A metal coated product’s life is ultimately decided by the environment it is exposed to, the amount of coating metal applied to the base steel and the eveness of its application. Our ZINCALUME steel has a guaranteed minimum coating mass of AZ150g/m² and that is your guarantee of long life performance.” said Wayne Miller.
Contact BlueScope Steel
T +27 21 442 5420
F +27 21 448 9132