Roofs constructed with the combination of king & queen post roof trusses are a mansard truss, truncated truss and king and queen post truss.
King and Queen Post Truss:
Queen post roof trusses alone are suitable for span up to 13.5 or 14 meters. Spans greater than 14 meters, modification of queen post truss is carried out by introducing one or more upright member and the diagonal braces. Adding one upright member called princess-post can strengthen up the queen post truss and makes it feasible for spans greater than 14 meters.
This truss is divided into two parts. The upper part of this truss is king post truss and middle to lower part is queen post truss. This roof also consists of the diagonal braces which are located near the queen posts and the ends of the tie-beams. This truss is suitable for spans up to 18 meters. Figure underneath shows the typical type of combination of King Post Truss & Queen Post Truss.
01. Mansard Truss:
This roof is also the combination of king post truss and queen post truss. Francois Mansard is a first designer of this truss. It is called mansard roof.
It is a two storied truss. The upper portion of this truss is integrated as king post truss and the lower portion of the truss is integrated as queen post truss. The entire truss has two pitches. The upper portion of the pitch varies from 30° to 40° and the lower portion of the pitch varies from 60° to 70°.The use of these roof trusses results in economy in space, since a room may be provided between the two queen-posts. These roof trusses have become obsolete because of its odd shape.
02. Truncated Trusses:
A Truncated truss is similar to mansard truss but its top is formed flat with gentle slope to one side. Truncated truss is used when it is required to provide a room in the roof. This room is located between the two queen posts of the truss.
