Yurt Perimeter Drainage Solves Humidity Problems

Perimeter drainage
Spring has proven to be a real test for our yurt. To close out the late fall and early winter, we experienced exceptionally unusual rainfall and early snowfall. Because we have built our yurt on the slope of a hill, the deck on which the yurt rests is at ground level at the rear, and fifty-four inches off the ground in the front. This permits good air flow, but demanded that we hoard the perimeter to block cold air infiltration. Unfortunately, the hoarding also trapped humidity, and we experienced numerous condensation issues throughout November and the first week of December.
The interior of the yurt is lined with foil-backed bubble insulation, with all joints taped. This makes for a very air-tight unit, but any moisture inside is trapped, as well. Cooking, showering and even everyday living contributes to the high humidity. We experimented with a number of options to reduce this wet air, with limited success.
The major problem was that, because it was winter, we needed to seal and insulate our rooftop vent. This creates a dome where the heat rises and remains somewhat trapped at the apex. Although the yurt is quite warm and well insulated, there are many partial thermal bridges, at the headers, the window framing and even at the roof ring and rafters. As soon as we reduced interior temperature, the cooler outside air would condense humidity on the foil, which would accrue and run down the walls or drip from points of the roof.
Using a fan at the peak of the dome ameliorated the problem, to a degree. Similarly, by adding insulation between the tarp and the exterior wall framing, we were able to reduce the temperature differential. Lastly, we reduced our interior temperature by a couple of degrees and maintained that temperature day and night.
The major problem that remained was the moisture in the soil under the yurt. This spring, moisture levels have been exacerbated by heavy rainfall and a slow thaw that releases the moisture in the ice slowly.
This week, we believe we resolved that issue. By trenching around the perimeter of the yurt profile to a depth of six inches and six inches wide, we have created a mini-drainage ditch. This U-shaped trench catches the rainfall as it falls from the walls, and directs it along the perimeter of the yurt, then away. There is no opportunity for the water to pool under the yurt and contribute to the humidity issue.
Although it is early in the experiment, it seems to be working. We have experienced no condensation issues in the first three days. Yesterday, the spring rains hit again, but there is no water under the yurt, and our humidity inside the yurt is no higher than the outside.
As we move through each of the initial seasons in our yurt, we have discovered new challenges and issues that would be uncommon in conventional housing. However, in spite of the spate of concerns, both of us are thrilled with this innovative living accommodation and its two overwhelming benefits: a miniscule cost (with no mortgage to pay) and its roomy in-touch-with-nature atmosphere.

Yurt Exterior Skins

Our yurt is designed with two exterior tarpaulin skins. The inner layer is a commercially available tarpaulin skin, intended to provide a secondary protection against rainfall, and a buffer to reduce the amount of friction of edges of the structure against the heavy-duty uv-protected tarpaulin.
The tarpaulins were purchased from Cover-Tech (New Brunswick, Canada), who provided the lowest price quote for a 12 ounce tarpaulin.
The two pieces were custom made, with the wall tarpaulin being 94 feet long and 7’6” high. The extra length will be used to lap over the doorway when we are away for long periods of time. The height exceed the height of the wall structure by six inches, to allow for overlap at the top of the wall framing (under the roof tarp) and excess length at the bottom to allow for water runoff and reduce inflow of cold air in winter. The roof tarp, too, was ordered at 30 feet in diameter, while the yurt was built to 28 feet. The extra foot around the perimeter provides enough material for us to create a partial awning over the windows, to deflect rain and snow.
A small problem occurred with the roof tarp that was easily remedied. The roofline angle (slope) was calculated at 30 degrees. However, after seaming, the tarpaulin was sewn at a 33 degree angle, and our rafter cuts were out by 2 degrees. As well, while the tarp is manufactured as a circle (cone), the yurt actually consists of 44 straight-edge sections. This resulted in a loose fit of the tarp. Normally, this would be a severe problem, as the flutter of the tarp in moderate winds would exacerbate the degrading of the tarpaulin. However, our roof vent design allowed us to snug the tarp over the vent frame, and use only one tuck of material around the entire cone area.
Once the roof tarp was hoisted into place using pulleys and ropes, the wall tarp was erected, and the top edge snugged under the lower edge of the roof tarp. Using a series of ratchet tie-downs attached together, we tightened the straps around both the upper and lower perimeter of the wall tarps, holding the roof top securely against the wall tarp. To ensure that the roof tarp did not free itself from the tie-downs, polyester rope was threaded through the tarp eyelets, and the ratchet tie-downs fed through the rope loops.
Lastly, we cut three-sided openings in the wall tarp for the windows and doorway (the fourth upper side was left uncut), retaining the material to use as a roll-down sunshade.

Weather Wrecks Yurt Plans

Designing, constructing and living in my yurt was supposed to free me from more mundane housing concerns, cut costs, and make life more simple. Ha!
Since beginning construction on my own yurt design, I have been slapped with an important lesson: Nature rules. In our region – a normally dry, stable area in western Canada, late spring should be an ideal time to build. But record rainfall has flooded three of four western provinces, and, in our case, washed out access roads, and so severely restricted access that I have been forced to bring building supplies strapped to my back! We, fortunately, have had two days when we were able to work a supply truck across a neighbouring farm field. So, construction, severely delayed, still has moved forward.
Today, we are working on erecting the wall shells, with the roof rafters scheduled for tomorrow. Today, we will be working in thunderstorms, while tomorrow we will be working in humid, sticky heat.
Throughout this preliminary period, I have picked a total of 396 wood ticks off my legs, arms, back, scalp, etc. It is a record of which I am perversely proud! But, with the tick count cropping, the flood waters receding and the humidity & heat rising, a new nemesis has crashed the party: mosquitoes.
In the mid 1990s, Pioneer Quest tracked a year in the lives of 2 modern pioneer couples, who were required to build a cabin, break the land, and live precisely as pioneers in the area did in the 1800s. Those couples were inundated with natural disasters that year: excessive rainfall, exceptional summer heat, wicked mosquitoes and high snowfall & cold temperatures in the winter. It looks like we are on track to enjoy that same wonderful blast of nature. So must for minimalism!
Later this week, I will be providing details on the yurt design we have chosen, and the source of supplies. As construction progresses, I will provide photos and details, so that you can follow in our footsteps. Bring an umbrella and lots of mosquito repellent!