Build A Yurt Rafter Ring, Version Two

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 ½ or 5/8 inch oriented strand board (or plywood, if OSB is unavailable) and a collage of two-by-four blocks.  Other materials needed include a pound and a half of 3 ½ construction or deck screws, a pound of 1 ¾ inch construction screws, enough 3 ¼ inch framing nails to allow for four nails per block, and a quart of carpenters glue or three tubes of construction adhesive.

Begin by cutting a four by eight sheet of OSB into four-by-four pieces.  Scribe a circle four feet in diameter in the first piece, and a circle three inches smaller in the second.  These will form the upper and lower  layers of the “sandwich” ring. 

Cut as many four to six inch lengths of 2 by 4 as you will have truss chords.  Lay out the pieces around the perimeter of the larger OSB circle, equidistant apart, with the pieces pointing toward the exact centre of the ring.  Mark the location of each piece.  Apply a layer of carpenter’s glue to each piece, and re-secure them in the spots as marked.  Once they have dried sufficiently, turn the assembly over and secure the pieces using two 1 ¾ inch screws per block. 

Measure the distance between each block at the inner edge.  Cut pieces of 2 by four that will fit accurately between each 4-6 inch piece.  Do not worry too much about angling the cut edges precisely, as these pieces simply act as stabilizers for the main blocks.  Apply glue to the long edges of these blocks, slide them into place between each 4-6 inch block and secure them using 3 ¼ inch screws, toenail angled into place.  Use one nail per longer block to nail the spacers into place.

Turn the assembly over again, apply glue to the exposed edge of all of the blocks, and attach the second ring, with its centre aligning exactly with the centre of the larger ring.  Use two screws per block, as in the prior side of the sandwich.  Turn the assembly over once again, and screw in two screws per spacer block.

This rafter ring is much lighter than the laminated version described in prior articles, and is much easier to raise into place.  With the smaller ring on the lower side of this sandwich design, the truss chords, once cut on the proper angle, will slide into the notches quite easily and will hold themselves in place as each truss in installed.  However, the drawback to this design is the tendency for the OSB to expand and weaken if it gets wet, or for the screws to pull through if they are set too deep in the OSB.

Yurt Drawbacks and Advantages

So you have looked at modern yurts, and are convinced that you would love to live in such a structure.  The salesman tells you all of the great things about the yurt (there are many), and you are more enthused than ever.  The price tag is presented, and you learn that yurts cost anywhere from one tenth to one fifth of a similarly sized bungalow. You are told that a yurt can be assembled within a couple of days.  So, knowing that you will be mortgage-free the instant that the home is erected, and you will be living in this space-age creation (that was first constructed several thousand years ago in the Slavic and Mongolian regions), you jump at the chance to go minimal with this unique idea.  But, there’s a lot more to be considered before you buy!

While yurts do hold great appeal, and while yurt living has a lot of advantages, there are myriad drawbacks, impediments and disadvantages to consider, as well as significant design and sizing options, depending on your region and geography.

Before we look at design considerations, reflect on a few of the more obscure issues that become very significant once you have moved in.  In our locale, for instance, we commune with nature in a very intimate way, with black bear, deer, raccoons & skunks, wolves & coyotes, weasel, mice, squirrels, an army of insects, garter snakes, birds and so on.  This interaction with nature is, for the most part, enjoyable. 

However, when the bear gets up close and personal, you don’t want to be cooking inside a flexible wall yurt, with plastic windows.  A solid wall yurt, raised off the ground is a must. 

When the skunks, weasels and squirrels take up residence under the building, there goes the neighbourhood.  Consequently, an effective mesh screen and lattice barrier is vital to keep the predators and vermin away.  Sure, the weasel will eradicate the mice, but that leaves the problem of a noxious weasel!  Skunks are fairly easily relocated, since they do not care to be in close proximity to us.  It is reciprocal.  Squirrels offer greater resistance and, like raccoons, can wreak havoc on the tarpaulins.  Our yurt integrates so well into its surroundings that a raccoon family has torn holes in the roof tarpaulin, merely by climbing onto it.  Squirrels leave only pin-sized holes, but more of them.

Birds are much more difficult to deal with. Their use of the yurt roof tarpaulin for target practice is a mere annoyance, but their clamouring across that same roof scratches the fabric as much as any squirrel.

Wolves are a great experience, while coyotes, after you have been away from the yurt for a week or so, do not hesitate to move in, burrowing little caves under shelters.

Insects, like mice, pose a major problem.  No yurt should have carpeting inside, because of the risk of ant, tick and spider infestations.  As tightly as you seal the walls and flooring, insects find entrances.  With flexible wall yurts, mice are a major issue.  This problem is eliminated with well-built solid wall designs.

Overall, though, the advantage of being in close contact with nature in your yurt outweighs the problems that such contact poses, if you prepare for these intruders and guests.  Because of the tent-like assembly, you are intimate with the outside world, hearing almost every sound.  As well, by using design and colour options (camouflage, etc.) for your tarps, the yurt may blend discretely into its environment.

The basic yurt design lends itself to several drawbacks. 

Flexible wall yurts, for instance, have walls that are less than two inches thick.  Even with the space-age bubble and foil insulation employed, you will experience more rapid heating and cooling variations inside this building.  However, a solid wall yurt can be constructed of conventional studding, and insulated to higher levels using fibreglass matt insulation as well as bubble & foil or Styrofoam foil combinations.  On the other hand, a yurt, because of its circular design and open concept, heats and cools much more effectively than a similarly sized bungalow.  For example, our 600 square-foot yurt can be heated during minus 25 temperatures with a small radiant propane heater (4-6,000 BTUs), and a 20 pound tank will last nearly a week.  A 600 square foot house would require triple that amount of fuel and still have cold and hot zones.

It is impossible to use standard glass windows in a flexible wall yurt.  Consequently, the norm is to install single-sheet heavy plastic windows, which transmit a great deal of the heat or cooling between interior and exterior.  A solid wall yurt, on the other hand, can accommodate standard window units (smaller sizes).  Doors pose similar issues, and, more so, because most yurt vertical walls are 6’6” to 7’ – less than standard door frame height.

Other infrastructure poses challenges, too. All wiring must be routed through conduit, as it is installed on the outside of the walls framing, rather than through it.  An option is to use low voltage wiring and inverters throughout the building.  Plumbing, too, is installed in plain view.  Of course, this method of installation is much easier and quicker. 

Due to the open design of these homes, privacy is impacted, and closet space is at a premium.  Creative layouts can offset these concerns.

Other considerations include safe heating systems.  Open flame is very risky in fabric yurts.  With solid wall designs, flame retarding materials and fire-rated wall boards can be installed.  Yurts may be purchased with mounting for chimney egress, but pay close attention to sparks that may burn through the roof tarpaulin!

Other problems that may arise include condensation issues in cold weather, when warm, moist air rises and contacts the thinly insulated ceiling materials, condensing and falling inside the building.  If tarpaulins (particularly roof tarpaulins) are not skin-tight, wind causes the tarp to billow which, in turn, packs down any matt insulation used and reduces that R-value. While the wind effect against a yurt is minimized because of the round design, this means that there are no leeward sides or areas next to the yurt, where you can huddle against the cool breeze.  That also allows smoke and loose sparks to migrate around the building during the winter.

Yurts, almost always, do not meet zoning demands of any urban jurisdiction, and, therefore, do not qualify for permits.  If you are building in remote locations, this will not be an issue, and some solid-wall designs, indeed, can obtain engineer certification.  Proper design and construction practices should be employed regardless of whether the building meets code.

Most of us choose yurts as our living option because of its simplicity and eco-friendliness.  Simplicity equates to Spartan, and Spartan means less luxury.  The yurt is simple.  That, in turn, should eliminate the expectation of opulence.  If you want opulence, stay in the city!  The yurt offers a wonderful escape and alternative to conventional housing, but be prepared for the drawbacks, as well as the advantages.

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.

The Romance Of Yurt Life, Wildlife Included

When you choose to live with nature in a yurt, it is a marriage: you accept the good with the bad. But even the bad can be great in the springtime! We have only been back in the yurt for a few weeks now, but our encounters with the wildlife have been nothing short of enthralling and amusing.
Last autumn, we closed out our season in the backwoods with a visit from a family of four raccoons, who systematically destroyed every bird feeder we had put up while they scavenged for the last meals of the season. A couple of squirrels determinedly decided to winter in the insulation under the platform deck of the yurt, as well, but we were willing to tolerate them for the four bitter months that we were away from our home.
As spring broke this year, though, we found just what damage a couple of active nut-eaters can do to insulation! Our raccoons have returned, as well. What is unusual is that the family of four remains together, with no new litter of kits in evidence. They announced their return by using their can-opener teeth to puncture a Coleman cooler that I had left outside. For dessert, they gnawed their way into a plastic gas canister, filled with mixed fuel for my chainsaw, and dragged the leaking container across the grass. Given their “finger” dexterity, I am glad I did not leave a barbeque lighter around!
Thirty miles north of us, Hecla Island, in Lake Winnipeg, is the summer home of turkey vultures and a few bald eagles. Rarely has either been spotted away from that area, yet, just as the snow melted from our meadow, a bald eagle pursued a mouse, and landed in the field to finish his lunch. It is just one example of the changing patterns of wildlife in the area. We have two mallard couples nesting in the creek bed not fifty yards from the yurt, sand hill cranes that have relocated their annual nesting area from the adjacent farmland to our small meadow, a grouse sitting on eggs under a three-foot high spruce in a clearing only paces from our home and coyotes that have decided that it is safe to howl, nightly, thirty feet away from where we sleep.
Late in the winter, I encountered a lone black wolf (probably from the Hecla pack) that obviously had strayed form its traditional range twenty-five miles north of us.
My wife is less happy with our annual migrant bear, who has, each spring and fall, travelled along our old riverbed with her latest cub. Two weeks ago, she came up to our doorstep with her cub, demolished a sealed garbage container and dragged one of the bags two hundred yards through our garden before tearing into it. As bold as that action was, she showed that she is less wary of human contact than ever, when she returned, during a rainstorm, to the yurt and rooted around the deck. In the morning, her huge paw prints in the wet clay where I had been excavating provided more than ample evidence of her visit.
Fortunately, our resident skunks and badger have not opted to become emboldened, and move in under the yurt platform!
More humorous that dangerous are the romantic interjections of local wildlife. Our ducks and Canada geese have almost finished their courting, calling, dancing and preening, while the frogs continue to be in great serenading voice. There is nothing quite so mood-destroying, though, as the cooing, gurgling and raucous clucking of crows in love. Their grating calls have all the appeal of a screaming baby. On the other hand, who can turn a deaf ear to the Buddy Rich drumming of a male ruffed grouse at 3:00 a.m?
The best of the strutting males though, has to be one of the many sapsuckers in the woods. For six years, he has chosen to drum his mating song not in nearby trees, but on any metal that he can find. Six years ago, it was my old Cockshutt tractor. Then, he found a better sound with an empty 45-gallon steel drum. Last year, it was the tin bonnet on my old camper. This morning, though, he reached the apex of quality music when he found that the roof of our new Prius provided the melody that he wanted.
It is there that I draw the line at passive interaction with nature. Tomorrow morning, I expect to join him with a few well-directed tennis balls to divert his attention from his new $30,000 toy! I expect, however, that, with the abundance of empty containers and old iron in the yard, it will be only moments before our rock-star drummer finds a new beat with which to lure his mate.