My Mother's House Part II: Building Our Earth Sheltered House

While the summer sun was still high, we made progress on our earth-sheltered house.

| September/October 1981

In the initial article about the construction of our earth sheltered house, we discussed the basic design concepts behind the planned structure, and we described the methods used to erect the dwelling's reinforced outer walls. Of course, our workers were anxious to get a roof on the building as quickly as possible to keep the rain out and the summer sun off their backs. And, as a result of their enthusiasm to get a little weatherproofing on the job site, in this issue we're able to tell you about the assembly of the internal roof-supporting-framework and the laying-on of the sheathing and insulation.

Post and Beam

While designing MOTHER EARTH NEWS' earth shelter, our team considered several different means of supporting the sod-covered roof on the front half of the house: precast, pre-stressed, and cast-in-place concrete, trusses, and even steel beams. But after hashing out the advantages and disadvantages of the various approaches, we finally chose to go with a wooden post-and-beam arrangement, because it could be economically built from local materials with basic hand tools and since we felt that the huge timbers required would be attractive additions to the dwelling's interior decor.

The vertical members (or posts) are 8 X 8 hemlock pine, which we acquired from a local lumber mill. Our original plans specified 6 X 8's, but the sawyer had only 8 X 8's on hand. So rather than wait to have the smaller timbers cut, we decided to widen the central wall thickness to 8" (instead of 6") to accommodate the larger members. Each post was secured to the slab with a 10"-long piece of 1/2" rebar that was pounded into holes in both the concrete and the wood. In addition, the posts at each end of the building were tied to exterior walls with 3/4" bolts.

A total of four more uprights were then positioned at 6-foot intervals from each end of the building, and the remaining quartet of vertical members was arranged so as to make room for a stairway and to provide additional support for a long central spanning beam.

Since an 8 X 16 kiln-dried Douglas fir timber would span the middle of the living area, with 6 X 12 hemlock beams as the remaining shorter crosspieces, the posts had to be longer beneath the big beam in order to raise it far enough to provide adequate ceiling height. (The 6 X 12's would become part of an internal partition, so their clearance wasn't important.) We allowed for this necessary jog by using longer posts and by setting the 8 X 16 atop the ends of the 6 X 12's. For added security, the beams were notched to a depth of 1 1/2" so that each post could be keyed into the horizontal timbers. In addition, all the posts and beams were joined with 1/4" steel plates and 1/2" bolts, nuts, and washers.

The rafters for the front half of the house consist of 4 X 12 sections of hemlock, spaced 36" on center. These 12' 10" and 13' 6" crosspieces span from the central beam (where the long ones were set on the 6 X 12's, and the shorter timbers were butted against the central 8 X 16 and suspended from 2" angle iron hangers) to one brick width short of the outer edge of the thermal mass wall. Then more brick was laid around and against the ends of the timbers.

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