A major roadblock in achieving substantial building energy reduction is the low performance of old buildings that account for a significant portion of the building energy consumption. Finding low-cost energy retrofit solutions that do not disrupt occupants' daily life during the retrofitting is the key to successful building energy retrofit initiatives. In this paper, a novel and low-cost exterior wall retrofitting solution is introduced, and its performance in reducing space cooling load was quantitatively evaluated to demonstrate its feasibility and effectiveness. The primary goal of this paper is to provide a quantitative assessment of the cooling-energy savings potential by using the proposed new wall system. The intended retrofitting targets are the large amount of existing cavity-wal buildings located in hot climate regions. The quantification of the before-after heat-flux reduction was conducted through a 3-dimensional steady-state low turbulence computational fluid dynamics (CFD) model, which is validated by benchmarking its prediction against the published experimental case results. The outcomes of the investigation suggest that this simple low-cost solution has great potentials in reducing buildings' summer cooling load in hot climate regions. The applicability of this solution is not limited to retrofitting existing buildings. New energy-efficient building designs can also adopt this solution in their envelope systems.