In flexible wall yurts – the most popular designs – the
outward stress is counterbalanced by a line of aircraft wire strung through the
vertical wall lattice, and tensioned using a turnbuckle system. The rafters notch into this cable, pressing
outward in a uniform manner. Because of
the circular shape, every resting point of the heels of the truss chords
applies equal pressure, and thus, each truss offsets each other truss. At the apex of each chord, the rafter ring
bears the weight and pressure of the upper end of the truss, equally and
counterbalancing each other truss. This
design is simple, but its simplicity means that there is a maximum diameter of
yurt that can be built.
Solid wall yurts have both drawbacks and advantages over the
lattice wall design. While they offer
greater protection from exterior elements, the ability to be designed taller
than lattice wall units, the flexibility to incorporate conventional doors or
windows and the capacity for greater insulation, they also have the drawback of
being built in a multitude of wall segments, as opposed to the continuous wall
format of lattice walls. Solid wall yurt systems require, because of the
individual wall panels, supplementary structural support.
When designing my solid wall yurt, I incorporated not one,
but four rafter support concepts.
The first was the conventional aircraft cable, strung
through the heels of the rafter chords (reinforced with a metal ring, to
prevent cutting through the wood of the rafter.
Secondly, I used hurricane ties on each chord heel. Thirdly, I nailed steel mending plates at the
top and bottom of each joined segment.
The fourth concept provides unique structural support for
the walls, offers exceptional wind resistance, and ensures that the rafters do
not place excessive force against the top of the walls, causing them to bow
outward.
My yurt is twenty-eight feet in diameter. Using forty-four two-foot wide panels, I
placed each panel at an eight-degree angle to the adjacent panel (resulting in
352 degrees of curve, rather than the full 360). By using 2 by 6 studs and
cutting an eight degree “V” shaped 1.5
inch wide, I was able to generate 12 top plate segments from each eight foot
length of wood. Each piece has two arms
extending from the apex of the “V”, with each arm twelve inches long.
These pieces are nailed on top of two adjacent panels, with
the “V” placed precisely where the two pieces meet, and extending one foot into
each panel. They are secured with three
nails in each arm. As added
reinforcement, I used the same system as the bottom plate for the walls.
This unique top and bottom plate system has worked
exceptionally well, with the yurt enduring wind gusts of 115 kph (73 mph)
without any problems. In fact, in 2011, shear wind toppled a tree with a trunk
diameter of fifteen inches, less than 100 feet from the yurt. The yurt barely quivered! 2010 winter snow loads failed to bend or bow
any of the truss chords. Although I clearly have implemented more
structural reinforcement than is normally required, the strength of the design
provides comfort and reassurance in the harshest weather.
