Effects of design and operating parameters on green roof thermal performance in Melbourne

The growing interest in extensive green roofs prompts more refined studies on green roof design and operation. To assist in the design, installation and operation of green roofs, the effects of design and operating parameters on green roof thermal performance need to be fully understood. The effects of two design parameters: substrate thickness (ST), conductivity of dry soil (CDS) and four operating parameters: leaf area index (LAI), leaf reflectivity (LR), stomatal resistance (SR), moisture content (MC) were investigated using the green roof model developed by Sailor in 2008. The sensitivity analysis revealed that among the operating parameters, LAI has the largest effects on thermal performance. On the other hand, between the two design parameters CDS is more influential than ST. An experimental investigation in Melbourne of non-vegetated green roofs with three substrate thicknesses (10 cm, 15 cm and 20 cm) and on a bare conventional roof was employed to isolate the effect of plants and enable better understanding of heat transfer mechanisms involved. In contrast with the sensitivity analysis, the experimental results for summer and winter showed the importance of the ST in reducing the substrate temperature and heat flux across the green roof. They also showed how the green roof substrate alone reduces the heat flux compared to the conventional roof. Finally, the thermal performance of sparsely vegetated green roofs in summer revealed a contribution to cooling effect of plants