This paper presents a holistic decision support tool developed for use during the early stages of facade design. The tool is based on the interdependent relationships between facade performance, facade parameters, and conditions (environmental and spatial). It assumes that a decision maker has the ability to enhance the performance of a facade by making proper decisions on the design parameters in line with the conditions. However, since facade performance has various aspects (sometimes conflicting) to be considered at once, it is hard to predict the impacts of decisions on the overall performance. A single design decision may increase the performance in one aspect while decreasing it in other aspects. The tool aims to function as a guide to decision makers by indicating the impacts of design decisions on different functional aspects of facade performance from a holistic point of view. Functional requirements included within the tool are safety requirements such as structural stability and fire protection, health-related requirements such as weather protection (protection against water, air, and moisture), and requirements related to the well-being of the users such as thermal, visual, and acoustic comfort. Information provided in the tool is based upon an extensive literature review and structured as an Excel spreadsheet.