King Post Truss

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A King Post Truss is one of the most common types of roof trusses used on buildings today.

The King post extends vertically from a crossbeam into the truss, with the design connecting the apex of the triangular truss base, holding the beam.


A king post truss is also the simplest form of roof truss.  They are generally used for simple roof lines and short span bridges.  For a bridge, two king post trusses would be required on each side.  Roofs use as many side-by-side trusses as are necessary to create the desired size of the structure.  This type of truss is also used in aircraft construction.  In airplanes, the king post supports the top cables, helping to support the weight of the plane’s wings.

The History of the King Post Truss

King PostA king post truss was often used in medieval, Gothic Revival and Queen Anne architecture. The design originated in the 13th century and was commonly used in the 15th century. Examples can be found in European churches, tithe barns and bridges. The post is held in place by a collar beam rather than the central post of the roof truss.  The central post is referred to as the crown post. A famous example of this type of structure is the George D. Oakley house in Hawaii.

When to Use a King Post Truss Design

King Post TrussKing post trusses are usually used when there is a need to support the weight of an expansive roof. This type of roof provides not only functionality, but beauty as well. It has been an especially popular architectural choice in Great Britain.  The idea of these types of trusses is that the weight of the roof is evenly distributed along the horizontal beam, preventing sagging or damage. When the posts are used side-by-side, it is then called a queen post instead.

Limitations of a King Post Truss

A king post truss can only extend up to 30 feet; therefore, they are unsuitable for longer spans.  However, additional diagonal support can be added to make it a multiple truss system. This type of truss also does not provide storage space, because the frames are usually exposed, allowing no additional room.  In addition, if one timber fails, it can create a domino effect by overloading neighboring timbers and endangering the whole structure.

Conclusion

King post trusses are often used for homes barns, farm stands, pavilions, garages and carports. They are designed to add grace and elegance, as well as functionality to the home. The open, high-beamed ceilings also add a sense of space to a room.  While the structure is simple and mainly uses only two angle struts, it is effective and can be altered slightly to create additional support. Accessing the roof structure to replace any damaged or rotted boards is also a simple process.

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