Benchmarking Lab Wind Performance with In Situ Monitored Data of Modular Vegetated Roof Assemblies

The National Research Council of Canada (NRC), as part of a consortium with members from vegetated roof industries and roofing associations, established a national wind resistance standard for modular vegetated roof assemblies (MVRAs), named CAN/CSA A123.24, “Standard Test Method for Wind Resistance of Modular Vegetated Roof Assembly.” Currently, this standard is widely used on a voluntary basis by the Canadian roofing industry for wind performance compliance of MVRAs. CAN/CSA A123.24 was developed based on extensive data collected on various MVRAs by simulating wind in laboratory conditions. Toward codification of CAN/CSA A123.24, the consortia members decided to validate such collected data with in situ performance data. This paper presents and discusses the validation process. Different MVRAs were installed on the rooftop of a Humber College building, located in Toronto. The validation was conducted by comparing the three wind performances of MVRAs as follows: (1) pressure equalization (between the top and bottom of the vegetated system); (2) coefficient of lift, $C_L$; and (3) estimated overturning wind speed, $U_{\mathrm{OT}}$, at different wind conditions. Data comparisons (laboratory versus field) showed consistent agreement in the global trend. Some discrepancies in the absolute values were observed; however, these discrepancies are due to the inherent variability of the field wind conditions and the limited amount of field data. The forecasting of the overturning wind speed provides a valuable tool to adequately evaluate MVRA design alternatives for acceptable wind resistance compliance in accordance with the National Building Code of Canada.