Prefabrication of timber envelope components is a constantly developing research field, which attracts interest from various sectors of expertise thanks to the conspicuous advantages it can confer in terms of resources savings, as well as quality management and safety for all actors involved in the process. The present paper goes through the design of a newly conceived external wall system for tall CLT buildings, entirely preassembled off-site and so able to be installed on his final position via crane, renouncing to scaffolds for the façade completion. This not only allows for the construction phase to speed up but also for immediate protection of loadbearing timber elements from weather agents exposure. The work follows three main phases: the functional analysis and layer definition, component design through bi-dimensional study of joint operating mechanism and tri-dimensional validation of the system. Main author findings outline how success of prefabricated systems and their durability over service life is strongly dependent on the effectiveness of joint design.