Modeling the heat diffusion process in the abiotic layers of green roofs

Chi Yung JIM, S.W. TSANG

Research output: Contribution to journalArticlespeer-review

59 Citations (Scopus)


Green roofs have been increasingly installed to alleviate some common environmental problems. The thermal benefit of living vegetation on rooftop has been extensively studied. The individual and joint contribution of the non-living green roof layers, namely soil, rockwool (water storage) and plastic drainage layers, to thermal performance of green roof has seldom been assessed. This study evaluates the insulating and cooling effects of these abiotic materials. A one-dimensional theoretical model was developed to assess the heat diffusion process in the layers. The model was validated with empirical results from three experimental plots. A calibration procedure was successfully applied to determine key model parameters. The model can capture the most critical features of temperature variations and thermal performance of common abiotic green roof materials. The appreciable water-retention capacity of rockwool plays the dual role of supplying water to the soil to enhance evaporative cooling, and increasing the specific heat capacity of the green roof. The plastic drainage sheet with ample air spaces serves as an excellent thermal insulator. The model remains robust despite seasonal and weather variabilities. Our research findings contradict with some researches in the temperate region that the thermal dissipation in green roofs with dense vegetation is lower than thermally insulated bare roofs. The theoretical model could be used to simulate the micro-environmental conditions and predict the thermal performance of different materials to improve green roof design. Copyright © 2011 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)1341-1350
JournalEnergy and Buildings
Issue number6
Publication statusPublished - Jun 2011


Jim, C. Y., & Tsang, S. W. (2011). Modeling the heat diffusion process in the abiotic layers of green roofs. Energy and Buildings, 43(6), 1341-1350. doi: 10.1016/j.enbuild.2011.01.012


  • Green roof
  • Thermal performance
  • Evaporative cooling
  • Heat diffusion
  • Wet porous medium
  • Abiotic layers
  • Theoretical model


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