You may refer to a truss as the rafter, but it's basically the skeleton of the roof, carrying the weight of the frame and supporting the walls of the building. Trusses are very important to preventing the walls from bending or flexing, more so.
KAIROS / João Quintela + Tim Simon Attention to detail I guess the idea was that the stair can be a part of building skin. For that, the architect made new type of stair. Actually the stair does not exist itself.