GO UNDERGROUND IN MICHIGAN
(Page 2 of 4)
November/December 1978
By the Mother Earth News editors
We decided upon southern pine — pressure treated at 50 to 60 pounds per square inch — because it's water-repellent, resists fungus and rot, and doesn't appeal to termites or other insects . . . and I worked out the stress loads and angles myself with the help of a machinist's handbook. Most folks could run these calculations themselves, but my 38 years as a tool-and-die maker made the figurin' especially easy for me.
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Just to be on the safe side, we added a layer of 6-mil black polyethylene waterproofing — between the wood and sand — to all of the building's earth-facing surfaces. The plastic sheet should have a life span of at least 50 years in this particular application.
All the dwelling's walls were built from 3/4" treated plywood and nailed — with hot zinc-dipped fasteners — to 2" X 6" pressure-treated studs. These supports are placed 12" on center to assure the strength of the structure. Then, to make these surfaces even more sturdy, we reinforced all of the earth-covered walls with diagonally braced sheets of 3/8" plywood before the sand was piled on.
The roof was constructed from treated pine plywood, too . . . nailed to 2" X 12" ceiling joists which were placed 12" on center the same way the studs were spaced in the walls. This wood was then covered with five layers of felt — which we applied with mopped-on hot plastic roofing cement — to reinforce and waterproof the "top" of Joyce's home. Then, over the fabric/glue mixture, we added two layers of the polyethylene and two inches of styrofoam, with a four-inch plastic drainpipe (which carries the roof water off and deposits it in the surrounding soil) sandwiched in between. We covered this "layer cake" roof with an average of eight inches of sand, black loam, and forest sod . . . just enough to support local vegetation and a patch of blueberries and huckleberries.
That earth, of course, is our primary insulation. In addition to it, however, we had 12 inches of cellulose blown into the ceiling and packed six inches of fiberglass into the walls. We also installed a number of Andersen tripleglazed Windowalls . . . which let the sun in without letting out too much heat in the process. I knew we'd insulated well enough when the snow on the roof melted at the same rate as the drifts in the surrounding countryside.
In order to comply with a local township building code — and because Joyce wanted windows in every room — we left 22% of the house's outer surface exposed. These "naked" walls were dressed up with redwood siding.
