Assessment of the potential use of recycled polyethylene as a green roof drainage layer

A growing trend regarding green roofs is the use of recycled and reused materials in their drainage and substrate layers, which can generate environmental, technical, economic, and aesthetic benefits while also providing the possibility of incorporating waste into the construction production chain. Except for the substrate, very few studies have investigated the potential to use recycled materials in other green roof layers. This article evaluates the thermal properties of polyethylene granules, derived by the recycling of waste plastic films used for greenhouse covering, as drainage layer in green roofs. To this end, a laboratory testing method was proposed to assess the thermal conductivity of drainage layer materials. The tests were performed for the recycled polyethene, expanded clay and perlite, these last as commercial products, by varying the water content. Thermal conductivity measurements were conducted using the HFM 436/3/1 Lambda and the TLS-100 equipments to cross-referencing the measurements. The results demonstrated that. perlite had thermal conductivity lower than both expanded clay and polyethylene in both moist and dry conditions. Differently, by increasing the water content, perlite had the highest thermal conductivity due to the hygroscopic material structure and polyethylene had the lowest thermal conductivity. This result is significant because recycled polyethylene, being a recycled material, can increase the sustainability of green roofs while reducing costs compared to expanded clay and perlite. In addition, by comparing the thermal conductivity determined with the proposed testing procedure to the thermal conductivity provided by the perlite manufacturer, it can be observed that the results are similar. Therefore, the proposed testing method may be considered reliable, and it could be used for the evaluation of the thermal conductivity of granular materials.