Mother's Bioshelter Greenhouse
(Page 2 of 4)
July/August 1986
By the Mother Earth News editors
Rodale's greenhouse has rock under the beds to offer mass for heat storage; a system that seems to work quite well. However, we've followed the lead of the Biothermal Energy Center (P.O. Box 3112, Portland, ME 04101) and the New Alchemy Institute and are composting various mixtures of organic matter in the bins beneath our beds. Though this technique is still in the experimental stage, it does have a number of both already-demonstrated and stilltheoretical benefits. The most obvious plus is that decomposing organic matter produces a great deal of heat: Our compost piles have reached 180° F and have maintained 160° F for more than a week at a time. Furthermore, the same material also yields moisture, carbon dioxide, and nutrients, which rise through the rocks and into the growing medium. These benefits are at least as effective as the heat input in increasing plant growth rate, but further experimentation is needed to determine the optimum mix of organic matter in the compost piles themselves. (NOTE: We'll have more about our work with composting for heat in the next issue of MOTHER.)
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Structure
The structure of the bioshelter is conventional. Six-inch block walls—reinforced in alternate cavities with concrete and 1/2" steel rods—rest on 8" X 12" poured footings. All of the masonry walls are either backfilled or bermed with earth for energy efficiency. Above the grade line, stud walls rise with insulated 2 X 4 framing. The roof framing consists of rafters on 24" centers. In the rear, 2 X 6 rafters are covered with 1/2" CDX plywood, 15-pound felt, and roll roofing. The spaces between the rafters are filled with fiberglass batt, a 6-mil polyethylene vapor barrier is stapled to the underside of the rafters, and the interior is finished with rough-sawed, random-width, board-and-batten siding. The glazed front roof must bear the weight of 3/8" tempered glass, so the rafters under the joints of the panes are full 4" X 6" beams. Alternate front rafters are 2 X 6s, and all the lumber contacting either glazing, sills, or growing beds is pressure-treated.
The array of diagrams and photos on the next few pages should offer sufficient detail to allow anyone with building experience to duplicate the bioshelter, but we'd like to share a few extra notes and tips that may be helpful.
Notes on Construction
The code: In our area, building inspectors are mainly concerned with residential structures and other buildings that have utility-connected electricity. For that reason, there were no restraints on how we built what is essentially considered an outbuilding at our site in Transylvania County, North Carolina. Though we're confident that our greenhouse is structurally sound, you may find that aspects of our design won't meet your local code. For example, below-grade, 6" block walls—no matter how well reinforced—aren't allowed in some areas. So be sure to check with your building inspector concerning the details of this design before you begin construction.
