Unique Yurt Top Plate Design Provides Exceptional Support

While yurt construction is relatively easy, there are several critical considerations to be factored into your design.  Yurts appear to be flimsy structures, supposedly nothing more than a slightly more rigid form of tent.  Yet, these innovative buildings have been the mainstay of tribes of the Himalayas and northern Middle East for tens of centuries.  One of the most vital considerations is the counter-play of the outward pressure of the roof rafter system against the vertical walls, along with the gravitational downward pull on the roof truss chords.

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.

Building A Yurt In Winter

Building a yurt may not be at the top of your desirability rankings in the dead of winter, but, with proper planning, a quality structure can be pre-fabricated, then assembled on site in a matter of a few days.  While flexible-wall, tarpaulin yurts are the most popular structures in North America, it is the solid-wall yurt that provides the greatest protection, for the lowest cost in cooler and colder climates.  Soft-wall yurts offer the primary advantage of being able to be assembled, then disassembled and relocated with relat9ve we, while solid structures do not lend themselves well to relocation. The question then becomes, if you intend to relocate frequently, why not buy a tent or RV?

Our solid-wall yurt will stand for years, and has proven itself, already, to be a weather-tight, comfortable home.  Although, due to our wanderlust and travelling nature in winter, we do not spent the deepest Part of winter in our home, it has endured the coldest, snowiest and windiest days of our Manitoba, Canada winters.  If minus-40 is still too warm for you, then a yurt, of any variety, may not be a viable living solution! 

By using 2-foot panels, assembled on an 8-degree angle to each other, we have constructed a 600-square foot (that’s incorrect:  hard to have square feet in a round building!) facility.  Similarly, one could build a yurt in a variety of diameters (12, 16, 24, 32) with relative simplicity. 

Simply construct the individual panels, cut the sectional top and bottom plates, build the roof ring and saw the appropriate angles into the roof rafters, and the entire package of components is ready to be shipped to your building site.  Assembly on your pre-existing platform or floor should take two people no more than 12 hours.  Slide the wall tarpaulins around this wooden framework, slip the roof tarpaulin over the rafters and install your doors and windows and your yurt is ready for the finishing inside touches.

The tarpaulin walls offer both aesthetic and practical benefits.  As a Tyvek-type exterior skin, the tarp is impervious to the most violent winds, while repelling both rain and snow. The roof tarpaulin, however, needs to be installed tightly.  This demands that the supplier manufactures it to your precise dimensions and pitch, and that your roof rafters and top plate assembly are equally precise.  If the tarp is too loose, any flapping or vibration in the wind will act as a billows, and dislodge your roof fibreglass batt insulation, or break the seal on your foil-backed bubble insulation used to line the interior of the ceiling.

Within two days, your yurt metamorphoses from a pile of dimensional lumber and fabric in your garage to a fully liveable home, for less than 50% of the cost of a conventional  flexible-wall yurt, and one twelfth to 1/6 of the cost of s similarly-sized conventional house.  The added appeal is that this project can be undertaken and completed at any time of the year.

Yurt Interior Walls

One of the great benefits of the yurt design is the open room concept. The lack of walls means that air moves freely. Combined with the round yurt structure, this means that a greater efficiency in both air movement and its contingent heating efficiency result. However, modesty demands that we build our homes with a private bathroom. Even in a yurt, this means walls, and a barrier to smooth air flow. Similarly, many of us want closets and wardrobes, whether they are built as standalone units or integrated into the bed enclosure. Again, the natural flow in the yurt is interrupted by such barriers.
In our yurt, we built a six by eight foot bathroom, but left the ceiling area open. While the walls do provide impediment to air movement, the open ceiling concept means that warm, moist air is able to move out of the enclosure, and reduce heat and vapour pooling. By combining our closet space into the rear, outer edge of the bathroom, we were able to reduce the number of structural breaks.
Still, these barriers created condensation problems within the yurt. In the late fall, cooler outside air and a lack of air movement in the corner areas where wall met outside wall, a severe moisture problem resulted, with development of mould. We solved that issue by implementing several strategies.
First, we installed small 12 volt fans in these vulnerable portions of the yurt. The fans were salvaged from desktop computers, yet are sufficiently powerful to move the air away from these stagnant areas.
Next, we doubled up on the insulation factor where floor, outside wall and inside wall met, installing a one inch thick segment of polystyrene rigid insulation, extending six inches above and below the floor level.
The third change that we implemented was to install two fans along the top plates of the bathroom and closet, forcing air to move from floor to ceiling.
By moving our furniture and small items away from the outside wall, we increased air flow.
Lastly, we bored two inch holes at the base of the wall, allowing the air to move freely between the main yurt floor space and the bathroom and closet.
It is imperative, if you are choosing to build a yurt for efficiency, that you consider what makes the yurt an efficient design. Vertical air movement, allowing hot air to rise in the summer and vent at the apex of the dome, as well as moving it downward with small fans in the winter, is a significant feature of the yurt design. It is more imperative, though, that you reduce barriers to air flow in dead spaces and “corners” of the yurt. Simple layout alternatives provide this free flow of air. Where possible, consider moving walls a few inches from the outside, and tie them together in a free-standing box system, so that there is a space along the entire height of the exterior yurt wall, keeping air flowing freely. Ensure that insulation is installed properly and evenly, with no cold spots to encourage dead air and condensation.
Built properly, the yurt design is a marvellous system. Done carelessly, and it loses its structural integrity and natural efficiency.

Solid Versus Flexible Wall Yurt Systems

Yurt purists will insist adamantly that its simply is not a true yurt if it has solid walls. Yet, the original yurts, from Turkey to the Himalayas, had neither tarpaulin skins or space-age bubble insulation and glass-domed vents. Yurts, indeed, are more about simplicity and function than any purist concept of how they should be designed, and from what materials.
It is true that the lattice/tarpaulin skin systems employed by manufacturers from Yurtco to Colorado Yurts have aesthetic appeal. Their flexible framing, bubble insulation and heavy-duty pvc tarps allow for an intimacy with the surrounding environment that a conventional house or cabin does not. The sound of rain on the exterior skins is magical, and the thick plastic windows create an aura of living in a tent. Even in relatively stiff winds, these yurts hold steady, yet react to the breezes. Yet, these same benefits also can be drawbacks.
Since windows are nothing more than thick, clear poly plastic, they transmit heat and cold easily. To cut down on sun infiltration, the exterior skin must be zipped shut. Similarly, in winter, those same windows almost always are zipped closed, creating a claustrophobic, tomb-like atmosphere. If the window is improperly installed and allowed to vibrate or shake, the plastic quickly breaks down, and, in a matter of a few years, the window must be replaced when it cracks.
The light lattice framing does withstand winds of 70-90 kph, but a wind/snow load supplementary support system must be installed in high wind/high snow regions. Of particular concern for many is the loose fit of the yurt wall skins at the base of these units. While tight enough to hold back the elements, many yurts with lattice wall design, according to owners, allow small rodents such as voles to work their way into the building during the colder months.
Due to the thinness of the exterior walls, R-factor levels for insulation are minimal, with only a few centimetres of space-age bubble insulation protecting against the elements.
A reasonable fear that some people have expressed is that the light construction is a poor impediment to a hungry bear, who may smell food through the fragile skeleton of the yurt. Whether the fear has ever materialized is irrelevant, as the fear may still exist even where the risk is minimal.
On the other hand, solid-wall yurts offer a great many advantages. Few bears, badgers or raccoons have the tenacity to force their way through 7/16 inch of wood, plus framing, making the structure seem considerably safer from these predators than flexible-wall yurts.
With the exterior tarpaulin covering those walls, wind and air infiltration is minimal. The framing allows for two to three times the insulative capacity than lattice walls.
Wind endurance is significantly greater in a properly designed solid wall yurt, as well. Using the interlocking top and bottom plate segments that has been created for these units, the structures have endured winds of over 115kph, without any sign of stress or strain. In one instance, a healthy tree, sixteen inches in diameter, was sheared off by the wind not more than forty yards from the yurt, yet the yurt suffered absolutely no ill effects from the wind force.
Window and door installation is easier and less expensive in solid wall yurts. Because of their framing, these buildings can be constructed using standard windows (double or triple pane) and doors, allowing for reduced cost, energy saving and better light infiltration. It is also a lot more difficult for a raccoon to claw through a pvc & glass window than a plastic one!
Along with the advantages of solid wall construction, these hybrid yurts maintain the tarpaulin roof structure, along with added truss strength to withstand heavier snow loads. The tarpaulin skin allows for the same magical enjoyment of a rainfall on the tent-like roof, the same intimacy with the outside environment and the same open atmosphere as more “traditional” yurt systems.
Yurt purists may decry the bastardization of their beloved structures, but they will have a hard time denying the advantages of solid-wall over flexible-wall yurts.