Case study: Cool roof energy savings

“In hot weather the air layer above roofs is subject to greater convective warming,   creating a micro-climate.” 

BlueScope and Stockland initiated a study on the effectiveness of cool roofing to reduce the cooling load of larger buildings. The results of the study carried out by Graham Carter of Lend Lease and University of Wollongong predicted that these savings could be greater than estimated using current energy modelling methods, which typically do not account for micro-climate heating effects above larger roof areas. 

While actual energy savings will ultimately depend on factors such as building type, roof size, building location, the study found that  “a savings multiplier of two to four is likely for any cool roof application over an air conditioned environment with roof top equipment.”

BlueScope building science innovation specialist, Mr Jamie Adams, associated the micro-climate above a roof to the phenomenon of urban heat islands, where dark and dense building materials absorb more heat than lighter-coloured natural surfaces, such as fields and forests. 

“In hot weather the air layer above roofs is subject to greater convective warming, creating a micro-climate,” said Mr Adams.“It’s much like the tarmac of a dark, hot road, where a blanket of heated air shimmers above the surface.” 

“A cool roof effectively reduces the amount  of hot air above it on a hot sunny day.  Cool roofs have high solar reflectance that minimises heat absorption by the surface. Cool roofs also have high thermal emittance to maximise the roof’s ability to shed away the heat that it does absorb.”