In practice, operable façade elements (OFE’s) in office buildings are often not appropriate to use to gain control over the thermal environment and indoor air quality. This study was performed to provide the means for architects and façade designers to design better usable OFE’s and improve personal control over indoor air quality and thermal environment in the future. Therefore, aspects affecting the usability of OFE’s was investigated, followed by determination of requirements, the design of an OFE meeting these requirements and the development of a Design Guide. This was done by combining a literature survey, database analysis and context mapping study. The literature studied contained on the one hand very specific information about the use and physical aspects of operable windows and on the other hand more general information on operable windows was part of the greater whole. The database analyses presented that objections of roommates, draught and noise from outside the building revealing the most important reasons for not always being able to open a window when needed. Besides, open answers gave additional practical insight and it was found that the increase in roommates decreased the positive response to always being able to open the window when desired. Thus, mainly explicit and observable knowledge where provided by the literature survey and BBA database analysis. The context mapping study learned that direct communication with users helps to understand their tacit and latent needs, which helped to provide the means to improve OFE designs in the future. The eleven requirements for better usable OFE's are: User-friendly, Clear design intent, Effective, Supply is fresh air of sufficient quality, Fine-tuning capability/adjustable, Low noise ingress, (Mental) connection with outside, Proximal/ highly controllable by occupants, Robust, Parallel use of windowsill and window and Align design and management & security policy. They should be seen in context with the illustrations and explanations in the Design Guide.