Solar Home Chronicles 14 Tuesday, 23 October 2007 Pouring the Foundation for our Solar Home The foundation of our passive solar home is the most important part of our home. After this, the rest of the construction looks much like any other energy-efficient (e.g. R-2000) home. Before the winter, we excavated our building site down to the hard pan. Then, we replaced the topsoil with a thick layer of broken shale. This was left to settle over the winter. Now, we smoothed out the shale, re-established the general outline of the house, and put down 8 inches of gravel. This was smoothed out and compacted (a good activity for an idle teenage son!). Now, the perimeter of our concrete slab was created using 2"x10" lumber. This was done very carefully - even an inch mistake would force us to re-design our interior. At this point we also called our plumber. He came to put in the water and waste lines that would run underneath the concrete. These included the kitchen and downstairs bathroom plumbing, the required sewer venting, and the lines that would be extended to the second floor inside future walls. All this called for accuracy and took some time. After this concrete set, it was another day when the knee-wall around the south-east corner, and the 9-foot wall along the north side of the house (against which our earth berm would rest) were poured. These also required much preparation - with electrical outlet boxes in the knee-wall and sturdy rebar in the north wall. One unusual characteristic of our concrete slab is that it has no footings. Footings are concrete extensions that go deeply into the ground to below the frost line, so that the house will not heave in cold weather. Our concrete slab foundation sits flat on top of the gravel layer, and we prevented freeze/thaw heaving by placing a 2-foot width of 2" extruded polystyrene insulation, covered with gravel, around the outside perimeter of the slab. Frost enters the ground at a 60 degree angle, so this insulation should prevent earth heaving underneath our foundation. My first impression of the finished slab was that it seemed much smaller than it should have. I overturned an empty bucket, and placed it in the `living room’ and looked out through where our 9-foot sliding glass door would be. I imagined where the future chicken coop would be, and gauged my view to the vegetable garden. It looked okay. I felt a soon-to-be-familiar sense of impatience and expectancy, as I considered what walls and windows would look like. Pressure-treated wood was placed to separate the concrete in the house area from the concrete garage floor, so that there would be no heat or cold conducted through the concrete between these areas. Once all this was done, a layer of 2" extruded polystyrene sheets was laid inside and up the sides of the wooden frame for the slab. It was important to insulate the slab so that it could function as a "thermal mass" to hold the heat for the house, once it was heated by the sun. In order to use the heat stored in the "thermal mass” of concrete, we laid a network of 18 5" air ducts on top of the insulation. These ran from a central point underneath where our stairs would eventually be built, and radiated toward outside walls, underneath future windows. When the sun warmed the concrete, the collected heat would be distributed throughout the house via these embedded ducts. A layer of plastic sheeting was laid along the bottom and sides of this unit. Then, the ducts had to be stapled down (using special plastic staples), to prevent floating when the concrete was poured. We had to wait over a week for a dry day to pour the concrete. Beginning where the ductwork originated, concrete was poured over the pad. Then, the garage area was poured, and smoothed down to its tapered entrance. Then, the rest of the slab was poured and smoothed down. Next week: which came first - the chicken coop or the house? Previous Article / Next Article