Building the Octangle Yurt
our fall construction project gets underway
After a day spend clearing the construction site, it was time to lay out the locations for the 4x6 treated poles that will form the main supports for the yurt. One way to describe the structure is that it's a sort of round pole barn in that the wieght of the roof will be supported by eight poles. Instead of the round shape we went with last year--which was aesthetically pleasing but involved a whole lot of detail work--this year we're going with an eight-sided yurt design. A true octogon has eight equal sides, but in order to better utilize construction materials, this yurt will have four sizes that are four feet wide alternating with four sides that are five feet six inches wide--which is why we're referring to it as an "Octangle."
The first step was to use two long tape measures to triangulate the points where each of the eight posts would go--drive a stake to mark the location, and move on to the next.
Then we fetched eight cement pads for the poles to rest on. These are things we make when we have a concrete pour and need to find something to do with the surplus concrete. At the least, they make nice stepping stones--in this case, they'll act to distribute the weight bearing on the pole.
Then started the chore of digging the eight holes some 30" deep. The way we approach that is to dig a bit, add some water to soften up the soil, and then return to dig more tomorrow.
Because the weather's hot and dry, there's a tendency for newly purchased wood to warp as the sun heats one side and not the other. In order to minimize that we're keeping the 4x6 treated poles in one of our shipping containers until they're ready to mount in the ground, and as a bit of extra insurance, Nikki painted them with a coat of stain/sealer. There's usually sealer left over from most any project, and this is a way to use it up--it won't matter if the colors don't match since the poles are going to be hidden away inside the walls.
Once the first hole was dug to a depth of thirty inches, the pre-cast cement plug was dropped in to serve as a base for the beam.
Then the first of the eight poles was set in the hole on top of the pre-cast plug. Supports where attached to keep it vertical as the post was checked and checked again to make sure it was plumb.
Before the pole could be cemented in, one last thing needed to be checked--we had to make sure that the pole was properly lined up with the outter wall of the cabin-to-be. To do that we temporarily installed a pole in the opposite hole, braced it plumb and then screwed a pair of sixteen foot long 2x6 boards to the faces of the two poles. At that point, we were good to mix.
We use a mix of 5 gallons of rock, 3 gallons of sand and a gallon and a half of portland cement, and when pouring into the ground like this, we go with a wetter mix that what's usually called for since the ground will quickly suck up a good deal of water. And that's fine in that what the liquid soil will be taking in contains some of the cement. When that sets, it will harden the soil that's in contact with the cement thereby increasing the pole footing's overall strength.
With the first pole cemented securely in place, the next task involved setting the next three posts to form one of the two main rectangles that make up the octangle.
The key here was to use lots of parrallel bracing to insure that the additional posts were the correct distance apart, all based off the first post.
After lots of checking measurements and plumb, it was time to crank up the cement mixer and anchor the poles into the ground. Four done, and four to go.
With the first rectangle cemented in place, it was just a matter of digging the holes and paying attention to detail to get the second rectangle in place.
Then another four cement mixes and all eight posts are in place and ready for the next step.
Today was an exceptionally calm day, so we used the afternoon work session to take down three dead trees that were close enough to Octangle to cause damage if they eventually came down the wrong way. We almost never cut down a live tree, relying instead of the natural cycle of life and death to provide enough wood to support our projects. In this case, the pine will be used to create planking needed to roof one of the containers down at the landing.
The space we needed to fell the trees in was narrow, but the use of guide ropes was sufficient to get the trees to fall just where we wanted them to. Over the years we've gotten pretty good at this, but it's never something to take for granted. For example, the first tree we cut got caught up in another tree creating what's known as a "widow maker" for very good reason. The problem was resolved by using the work truck to pull the trunk enough to get the rest of the tree to fall clear, and the next two trees came down without incident.
We finished the afternoon work session by digging the first of eight foundation ditches that will connect the posts together in a reinforced concrete ring, provide a foundation for the retaining walls, and a base to support the compressed earth brick veneer.
This late in the year, our clayish ground makes for tough digging, so one trick we use is to take time to water the ground ahead of time. The goal is to dig just enough dirt so that the undistrubed earth can act as the form for the concrete footing, so precision is more important than speed at this point.
Before getting started on Octangle, Sean helped to run some of the limbs from the three trees through the chipper quickly putting away another 100 gallons of wood chips for use this winter.
Getting back to Octangle, the next step was to take the 1/2 inch power drill and make holes through the poles for the 1/2" rebar to pass through.
After passing through the poles, the four lengths of rebar were bent to a 45° angle to follow along with Octangle's foundation. Then additional sections of rebar were used to join the four sections to create a complete ring of rebar to tie each pole into the foundation and wall risers.
An outer ring of rebar was installed to hold the footing together, followed by bent sections of rebar to connect the two runs.
With the rebar in place, it was time to start up the cement mixer and begin filling in the footing. Eight mixes took us half the way around Octangle; we'll get the rest next week.
Re-use is a key part of sustainable construction, so we keep an eye out for appropriate materials that we can incorporate into Octangle. For example, we picked up four matching windows for Octangle from a friend who deals salvage in The Dalles.
We were able to stop by The Bins in Portland this weekend, and found a set of four sort-of-round light fixtures that will provide an interesting accent. Four light fixtures may seem like a lot for a small structure, but they'll be individually switched so that instead of the usual practice of lighting an entire room, we'll be able to light just the area needed, thereby conserving energy--a technique that works in this case because we were able to buy the four fixtures at The Bins for less than one fixture would have cost us at Home Depot.
This evening's cement mix saw the last of Octangle's footing poured.
Which brings us to the point of needing to mark a level plane so that we'll use to set the riser forms. That involved setting up a rotating lazer that marked each post with its ruby red beam, a mark that we made permanent by driving a duplex nail through a bit of pink flag tape to make a reference point.
The task of pouring the riser starts on the back of Octangle where the surrounding ground is the highest. We made up a form for the six foot side and another for the four foot size, and we'll just keep moving them around each day until the foundation's finished.
Each evening we're pouring a quarter of Octangle's risers--as of sundown today, we had three-quarters of the risers poured.
Last of the risers poured--not satisfied with the levelness of a couple of the risers, but one of the nice things about pole buildings is that since the roof is help up by the poles, all the walls have to do is fill up the space between the poles. We'll deal with the imperfections when the walls go in, and once the sheet rock is in place, the imperfections won't show.
Notes From Windward - Index - Vol. 67