Transpired Solar Collectors (TSC) are promising solar energy solutions and represent a sustainable alternative strategy to mitigate energy consumptions for space heating, preheating of fresh air or drying purposes. During the last 30 years TSCs have been extensively investigated by mathematical and experimental study. However, despite intensive studies of TSCs certain parameters, essential for the design of TSCs, remain uncertain in the literature, such as the air plenum thickness. We therefore analyzed the influence of the air layer thickness of a novel double skin transpired solar collector through a numerical study. The numerical investigation shows that for thinnest air layer thickness the perforated absorber plate overheats in the upper part this leading to a loss of heat that could be extracted from the collector. This study provides an understanding of the impact of the air plenum thickness of a solar facades to be more comprehensive for engineers and architects in their designs.