Font Size: 

Green roofs are complex engineered structures that can provide significant benefits to biodiversity, the thermal performance of buildings and stormwater management, amongst others. As such, there are guidelines that dictate the composition and properties of green roof substrates to ensure that these benefits can be realised. However, a green roof’s position exposes it to several natural processes that may alter the properties of the substrate beyond their allowed limits. There is currently little understanding of the presence and magnitude of changes to substrate properties as a result of influencing processes over time. This paper uses techniques not used before in a green roof context to non-invasively explore the internal structure of two green roof substrates in both aged and virgin forms. Using X-ray microtomography and image processing techniques, particle size distributions and porosity values are determined for selected 2D planes. It is found that the X-ray microtomography technique is a good method to non-destructively assess the properties of green roof substrates. The particle size distribution and porosity of the two substrates was found to be different between the aged and virgin samples. However, the uncertainties surrounding substrate heterogeneity mean these quantitative changes in properties should be considered to be indicative rather than absolute.