- Moves post away from the outside of the building.
- Simplifies the jointing of the structure.
- Creates a ‘cantilever’ effect, helping to support the tie.
- Creates something else for a theoretical structural archaeologist to worry about.
The king post truss is an elegant and simple solution that evolved from more complex solutions. From thousand of years of experience builders learnt that supporting the apex directly is unnecessary, and they slowly reduced the number of posts in the interior as experience refined what was felt to be safe.
However, if English timber roof building has a ‘apex’, it is the truly extraordinary Westminster Hall roof, (1394 –1402), built by Henry Yevele, the architect/builder, and Hugh Herland, the carpenter/designer. They replaced the aisled roof structure with a single 68’(20.72m) span hammer beam roof, using 1m thick hammer beams projecting horizontally 20’ to narrow the span and transfer the roof load to the masonry walls.
However, what ultimately restricts roof width and pitch is the length of timber available to form ties and rafters. Height, in terms of posts, is subject to same limitation. Precisely what this might represents, in terms of English oak, will be discussed a later article.
 Startin, W. (1978). "Linear Pottery Culture Houses: Reconstruction and Manpower." Proceedings of the Prehistoric Society 44: 143-59
 Clark G & Piggott S 1968, Prehistoric Societies, London, Hutchinson, fig. 85, p.273.