There are several designs of yurt rafter rings, each serving a particular purpose, and working best in specific environments. Snow load, wind and even humidity play a role in determining the most appropriate design. For the majority of yurt applications, the laminated design that I described in a previous article is the most effective. However, the design described in his article is suitable for smaller yurts (less than 32 feet diameter) and in low humidity locations. While it will withstand moderate snow loads, it is less structurally stable than the laminated version.
When designing a yurt roof, the same considerations that are factored into stressors on conventional housing roof rafter chords come into play. That is, you need to consider the tensions (both lateral and gravitational) on the angled chords. Truss chords endure two primary stress forces: the tendency of the bottom of the chord to push walls outward and the pull of gravity that causes slump in the riser chord. Use of collar ties works to ameliorate the gravitational warping, but, simultaneously, actually increases the stress on the top plate-to-chord heel point of contact. Fortunately, yurt roofs are so light that collar ties and webs usually are not needed.
In my prototype solid-wall yurt, I employ several redundant reinforcements for the chords. A series of mending plates, hurricane ties, aircraft cable and unique angled top plates create a structure that resists very significant outward stress. These concepts will be presented in future articles.
The rafter ring design in this article consists of two layers of
