Below is a clearer image of how such a building could be constructed, with end and side view. The sheathing and roofing material is left out showing only the bare structural members. On the side view, the diagonal bracing members run from the bottom left to the upper right; an additional set running perpendicular to these may be added to improve rigidity. The sheathing, once added, will also contribute to the strength of the building.
As all buildings, no matter how carefully conceived and crafted, are subject to eventual failure and dissolution, is there a way around this particular problem? As van Lengen describes the building, it is composed of lashed poles. In such buildings the lashings must be periodically tightened or replaced with new lashings. If built this way, then even if the ridge beam forces apart the joint it rests upon, periodical re-tightening will bring it back into its proper position. It is important to recognize that as builders, we often co-opt objects designed for one purpose and use them to fulfill another purpose for which they are only incidentally suited. A tree must only stand tall and bear vertical forces, but a building is composed of trees placed at many angles, and so joints are created that eventually will fail before the trees themselves do. If van Lengen's house were built of concrete, then the central equilateral triangle could be made without joints, or even turned into a catenary arch. If it were, there would be no problematic structural issues at all.
One solution arrived at hundreds of years ago is evident in the construction of the English "cruck house". The scale here is generally larger than the bamboo pole buildings described up till now. I had disliked the appearance of cruck frame houses, but now that I see them in a different light, they appear very interesting. Perhaps I could make a small one with poles?
photos of which are very instructive.
book documenting the entire process (a photo of one of his buildings is above). It was also featured on TV. Due to the careful attention to joinery details such a house would require, I would first build one like the cruck diagram I created, which I think would be simpler since it includes the "yoke", a detail excluded from Ben Law's design (though increasing its contemporary appeal).
3/20/10 I just got an inter-library loan book.
An interesting point and comparison of cruck buildings is made by N W Alcock, in his book Cruck Construction: An Introduction and Catalogue on the first page:
"Cruck trusses have only one essential joint, that at their apex holding the blades together. All their attached timbers can be removed or replaced, and even the feet (whether ground-fast or set on sill beams) can be reset without destroying their integrity. Furthermore, their apexes are well protected from weathering and decay. Contrast a box-framed building: its vital joint, between post, tie-beam, and wall-plate, is complicated, weakes the timbers, is exposed to the weather, and is unrepairable if it decays."I would add that this arrangement of two cruck blades is also a minimalist design, as any fewer, that is to say just one central post, would not provide sufficient stability for a building.