Glass/steel adhesive joints are being used increasingly in the construction industry as they offer significant structural advantages. While humidity and elevated temperatures are known to lead to the degradation of both the bulk adhesive materials and the bonded interfaces, quantification and prediction of the degradation effects are currently lacking. In this paper, the effects of elevated temperatures and humidity were determined and predicted by employing a combined experimental and numerical methodology. Bulk material and interface characterisation tests were performed to quantify the degradation of the bulk material properties and the glass/steel interfaces. Two numerical methodologies were devised and compared based on their ability to predict failure of glass/steel adhesive joints following environmental exposure, namely a continuum mechanics approach based on the bulk properties of the adhesive, and a cohesive zone modelling approach that assesses damage and failure based on the glass/steel interface properties. The results highlight the significantly different relative contributions of bulk property and interface degradation depending on the type of adhesive used.