Probabilistic approaches are needed to quantify and account for uncertainties in green infrastructure performance. One approach to quantifying performance reliability is through the use of fragility functions. Fragility is defined as the conditional probability of attaining or exceeding a specified standard of performance conditioned on different demand variables (i.e., loading intensity measures). Originally developed in the field of earthquake engineering, fragility functions have been used in multiple other applications, including flood control. This study developed a methodology to generate fragility curves for green stormwater infrastructure (GSI) to study the reliability of a green roof under different storm conditions. While the methodology was illustrated using a green roof case study, it is flexible enough to be extended to many other failure modes and types of green infrastructure.