Green roof substrate physical properties differ between standard laboratory tests due to differences in compaction.

Area of Science:

• Green roof technology
• Sustainable urban infrastructure
• Building science

Background:

• Green roofs offer significant environmental and urban benefits, driving international adoption.
• Effective green roof design relies on understanding substrate properties, but standardized testing methods are inconsistent.
• Discrepancies in substrate testing hinder the transfer of technological knowledge globally.

Purpose of the Study:

• To compare physical property characterization of a green roof substrate using European (FLL), North American (ASTM), and Australian (AS) standard testing methods.
• To assess the in-situ accuracy of laboratory-based standard methods by comparing results with measurements from actual green roof platforms.
• To identify variations in testing procedures and their impact on characterizing substrate bulk density, water permeability, and water holding capacity.

Main Methods:

• Laboratory testing of a green roof substrate using FLL, ASTM, and AS standard guidelines.
• Measurement of substrate physical properties: bulk density, water permeability, and water holding capacity at field capacity (WHC).
• Comparison of laboratory results with in-situ measurements of bulk density and WHC on green roof platforms.

Main Results:

• Standard testing methods yielded varied results, primarily due to differences in sample compaction techniques (Proctor hammer vs. free-fall).
• FLL and ASTM methods (Proctor hammer) resulted in higher bulk density and lower water permeability compared to the AS method (free-fall).
• Water holding capacity (WHC) did not significantly differ across standard methods; however, the AS method better represented in-situ bulk density and WHC.

Conclusions:

• Standardized green roof substrate testing methods require refinement to ensure consistent and comparable results.
• The Australian standard method demonstrates superior representation of in-situ substrate properties for mineral-based substrates.
• Minor modifications to testing procedures, such as Proctor hammer drop consistency for FLL/ASTM, can improve comparability and facilitate international knowledge transfer for green roof substrate design.