Diagrams: Figure 1 and Figure 2 side views of the sod igloo.
MOTHER EARTH NEWS STAFF
How I dug in for the winter by building a quick and inexpensive sod igloo to avoid leaving the woods of Vermont.
My predicament was starkly simple. With winter just a few months away, I had only a couple of hundred dollars, some basic tools, and my own two hands with which to build myself a temporary shelter for the cold season. To compound the problem, I wanted more than a mere refuge ... I hoped to create a dwelling that was not only warm and comfortable, but also structurally graceful and in harmony with the landscape of the northern Vermont forests where I make my home. After a good bit of research, I became convinced that I could fulfill all my expectations by building a semi-underground house: an inexpensive sod igloo.
I first encountered this uncomplicated design in the classic book Shelter (Shelter Publications, 1973). Ole Wik's description and photos of his sod "iglu", and Keith Jones's article about the building of a similar house in Alaska, convinced me that such a dwelling could combine the elements of efficient design with a simple sort of grace . . . and could do so while remaining unobtrusive.
Of course, these crude earth-insulated structures aren't generally used as permanent homes. Most often, they're intended as quick, comfortable, recyclable shelters that will serve until something more conventional can be built . . . or — on occasion — as auxiliary retreats, hunting cabins, and such. But with winter approaching, I knew the sod igloo would meet my needs and fall within the limits of my financial resources. In fact, in 1978 (the year I built it) the materials for my earthen cabin cost around $150 . . . about the same as had the goods which went into the canvas tipi I'd lived in previously. (And as someone who has experienced cold weather when protected by both, I'll guarantee that soil beats canvas as an insulating material every time!)
BUILDING AN INEXPENSIVE SOD IGLOO
It stands to reason that a sod igloo would be inexpensive . . . since many of the raw materials that make up such a structure can be had free. The necessary earth was, of course, stockpiled as I dug out the outline of the house.
I obtained wood for the frame, roof, and walls from nearby spruce and balsam firs. (Many of the required slim, straight poles can be culled from stands of young trees growing too close together for proper development. Because such an overpopulated copse produces trees that are tall, thin, and straight, a single thicket can provide an excellent supply of building materials and the opportunity to give Mother Nature a hand by thinning out her overabundance.)
The only other construction supplies I needed were nails, spikes, staples, a few screws and hinges, 6-mil black plastic sheeting for the vapor barrier, glass (you could use plastic instead) for the windows, planking for the floor, and 2 by 6's for framing the door and windows. And since I was able to salvage some of these materials and trade for others, my costs remained low.
My tools were basic, but well suited to the job at hand. The collection consisted of a saw, hammer, axe, hand drill, pick, shovel, drawknife, screwdriver, and staple gun. I also used a level and square . . . but only when laying the floor and hanging the windows. Peeled logs don't have many planes or right angles, so the builder must learn to work with the wood, using its irregular curves to best advantage. If this job is done with sensitivity to the natural grain and form of each log, it can result in a structure that is far too beautiful to be considered a mere shelter against the elements.
Because a sod igloo is an earth-sheltered dwelling, it's very important that it be built on a well-drained site, with the depth of the excavation well above the water table. I chose a relatively high spot in a small clearing where the ground sloped slightly to the south, and began to (laboriously!) dig out a hole that would eventually measure 3-1/2 feet by 15 feet by 18 feet.
After first removing the top layer of sod in one-foot squares and setting that future insulation to one side, I got down to the single most difficult part of my task . . . actually excavating the site. Digging the hole — working alone and by hand — called for about four 20-hour weeks of backbreaking labor, but finally it was completed . . . and I could get on with the more pleasant task of framing.
I started that job by placing the pilings, beams, and braces as shown in the diagram Figures 1 and 2 in the image gallery. The pilings form and support the basic 9 foot by 12 foot rectangle that defines the house, and they had to be thick (at least 6 inches to 8 inches in diameter), strong, and straight . . . since they bear a lot of weight, including that of two layers of sod and of up to three feet of settled snow during this area's rough winters. To fasten the beams to the tops of the pilings and the ridgepole to the beams, I cut simple square notches — in such a way that the log frame could withstand the compressive forces of the dirt that was applied later — and secured the joints with 10 inch spikes.
Since part of the front of the igloo was to be left uncovered (it would accommodate the windows), I knew that the earthen load on the back wall would be much greater than that on the face. And (I figured), without some extra bracing, the structure would eventually begin to lean away from the greater pressure, becoming unstable. Similarly, the side of the dwelling opposite the doorway would be subject to extra berming stress. To counter these forces on the back wall, I installed diagonal braces from the tops of the rear corner pilings to points near the bases of those in front, butting them against rocks buried below floor level. I braced the wall opposite the door in the same way, except that in this case the front prop starts below the window. Finally, I ran another support from the midpoint of the ridgepole to the beam above the window to carry the pressures from the back wall to the front without stressing the poles that would constitute the structure's roof.
Setting the walls and roof came next. The small trees I selected as my raw materials were each 4 inches or 5 inches thick at the base. (I needed almost 200 of them, but the woods at my building site are so thick that this depletion did little more than allow a few additional rays of light to reach my clearing.)
First, I cut and trimmed the young conifers and scraped them clean. Then I began to build my walls, leaning the poles against the frame at a slant of about 4-1/2 inches per foot of height. (I reasoned that, by doing so, I could use gravity to help hold the earth and sod against the walls . . . and allow the floor's dimensions to be greater than those of the ceiling.) I hammered each pole deep into the soil, nailed its upper end to the top beam, and sawed off its excess length. (For the sake of the inside appearance, I placed the poles as close together as I could, but an occasional gap — even as wide as 6 inches — wouldn't have done any harm, because the whole wall was sealed off by plastic sheeting later.)
I set the roof poles across the beams and ridgepole, nailing and trimming them as I had done for the walls. Then I laid the plastic vapor barrier in place and stapled it to the logs (more about that later) before beginning to build the earth and sod layers that would provide my new home's insulation against the cold.
It might have been quicker and easier to use boards or plywood for my ceiling and walls. However, the fact that the small trees I cut and peeled were available free-and already too thickly clustered for continued healthy growth played an important part in my choice . . . and so did the aesthetic appeal of the soothing visual rhythms produced by their irregular rounded shapes and natural wood grains, especially when seen by lamplight.
Indeed, after I'd worked so intimately with earth and trees in the building of my house, putting an exterior plastic covering over those gleaming shafts of wood felt like sacrilege. The vapor barrier was necessary to keep the dwelling dry and snug, of course, but I was still glad when it was hidden away beneath the mound of dirt and sod insulation that left my new home looking like an organic (albeit somewhat traumatized) part of the clearing.
At summer's end — after taking a two-month break to pick apples and bring in some much needed cash — I laid a plank floor, hung the door and windows, rigged up a woodstove and chimney, and moved into my sod igloo just before the first serious snow of the season transformed the Vermont landscape .
WHAT I EXPERIENCED
During the first weeks of winter, small beads of condensation formed on the plastic sheeting between the poles, and I was afraid that my shelter was going to be damp and cursed with mildew. But as the earth around the walls began to absorb the heat generated by my stove, the moisture disappeared. At the same time, living beneath a ceiling made from several feet of insulating soil and snow was proving to make both economic and aesthetic sense. Inside, I was warm and cozy . . . outside, the sod igloo now really blended into the landscape, looking like nothing so much as a large snowdrift miraculously puffing a thin trail of smoke.
While I didn't keep a pound-by-pound record of my fuel use during the winter, I generally spent about two hours every other day in finding, felling, hauling, splitting, and sawing enough wood (by hand) to keep me very comfortable through even subzero temperatures. In fact, when I sat reading and writing at my table by the windows on very cold but sunny afternoons, I had to keep the fire banked way down and remove most of my clothing in order to avoid being overheated. The igloo was always warm and inviting when I returned to it after a cross-country skiing jaunt, too, and at night the flickering shadows cast by my lamp along the naturally sculpted planes of beams and braces made me feel as though I were living in a work of art .
WHAT I LEARNED
That first winter in my earth-sheltered dwelling proved the structure to be a pleasant and practical home regardless of weather conditions outside . . . but if I had it to build over again, there are a few changes I'd make. While I had no trouble with rot attacking the underground sections of my support pilings, I believe it would have been prudent to treat the bases with creosote or old motor oil, or to char them as the Japanese do. I'd also support the beam over the windows with an additional piling (shown as "recommended" in Figure 2) placed midway across the front wall. And although my site was well-drained and I experienced no problems with flooding or seepage (even during the height of the spring thaw), next time I'd take the extra precaution of adding a floor drain to my basic construction plan.
The one serious flaw in my winter home was that the roof tended to leak during thaws and hard rains. I believe that the major reason for the problem was my obvious mistake in stapling the vapor barrier to the log roof, thus making holes that permitted water to creep through. But I also think that two sod layers atop the ceiling are probably not enough . . . especially in this wet climate.
In searching for answers, I found that the past several years have seen the publication of many good books about earth-sheltered housing. Most of the techniques and materials they call for, however, are too complicated and expensive to fit in with the simplicity and economy that are the chief advantages of a sod igloo. Only Mike Oehler's The $50 & Up Underground House Book seemed to offer a reasonable solution to my particular problem.
I've detailed Oehler's roof insulation scheme on the right-hand side of Figure 2. Mike covered the ceiling material first with building paper and then with 6-mil unstapled black polyurethane sheeting, maintaining a foot of overlap. Above that "foundation" he laid down four inches of stickless, stoneless, finely sifted earth . . . yet another layer of plastic . . . four more inches of clean dirt . . . and a topping of sod blocks. Of course, such a roof would be heavier, more complicated, and somewhat more expensive to build than mine, but I believe that it would result in a drier home.
On balance, though, my sod igloo was exactly what I wanted (and needed) to get through the winter. Inexpensive and relatively easy to build, it kept me comfortable and in good health through subzero cold and spring thaw. When I tally the cost against the rewards, I don't see how I could have chosen any better.
EDITOR'S NOTE: If you're unable to find the manuals mentioned above in local bookstores or libraries, you'll be glad to know that The $50 & Up Underground House Book can be ordered — for $8.95 plus 95 cents shipping and handling — from MOTHER's Bookshelf ®, Hendersonville, North Carolina.