“Treet” is a 14-storey timber apartment building in Norway currently under construction. Ground works started in April 2014, and the residents can move in autumn of 2015. The building will be one of the tallest timber buildings in the world. The building consists of load-carrying glulam trusses and two intermediate strengthened levels. Prefabricated building modules are stacked on top of the concrete garage and on top of the strengthened levels. There is CLT in the elevator shaft, internal walls and balconies. But, CLT is not a part of the main load bearing system. Glass and metal sheeting protect the structural timber from rain and sun. The paper presents the design of the building as well as many of the investigations, considerations and discussions which took place during the design process. Finally some of the design verifications are presented.