The Construction of MOTHER'S Bioshelter Greenhouse
(Page 2 of 4)
May/June 1985
By the Mother Earth News editors
The code: In our area, building inspectors are mainly concerned with residential structures and other buildings that have utilityconnected electricity. For that reason, there were no restraints on how we built what is essentially considered, in Transylvania County, North Carolina, an outbuilding.
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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.
Should you earth berm? Banking the walls of a building with earth is a good way to minimize heat loss . . . if the site lends itself to such a technique. We happen to have quite suitable slope and soil for earth sheltering . . . but we wouldn't necessarily recommend it if you're building on flat ground or in expansive clay. Instead, you might want to build with minimally reinforced concrete block (or simply frame the entire structure) above ground and increase the insulation level. There's also a good chance that this approach would prove to be less expensive.
Masonry insulation: Use extruded polystyrene foam, and add an extra inch if you experience more than 4,500 heating degree-days in your locale. Use either wire lath and stucco or a resilient stucco such as PennKote to protect the exposed insulation from sunlight.
Waterproofing: We don't consider small amounts of seepage to be a particular problem in a greenhouse, so the below-grade walls of the greenhouse are really more water- resistant than waterproof.
Floors: We used a 6" layer of gravel for our floor. A properly sloped concrete floor with appropriate drains would be nice . . . but expensive.
Pressure-treated lumber: Pressure-treated lumber has been specified in all areas that are likely to be moist. There are recognized hazards to the use of such lumber, but the only alternatives are very expensive: cypress, redwood, or some other rot-resistant wood. Believe us, standard spruce-fir boards will deteriorate quickly inside a humid greenhouse.
