Designing and Building a Recycled Greenhouse

Designing and building a recycled greenhouse with plastic drink bottles, aluminum cans and low-cost materials. Includes building information, greenhouse photos and diagrams and construction tips.

| December 1996/January 1997

Making permanent use of plastic drink bottles, aluminum cans, and elbow grease when designing and building a recycled greenhouse. (See the greenhouse photos and diagrams in the image gallery.)

Having lived most of our married lives in urban areas, when we retired in 1988, we wanted to experience a life of greater self-sufficiency. We had been subscribers to MOTHER EARTH NEWS for years and had some pretty good ideas on what we needed to do, starting with buying part of an old mountain farm in western North Carolina. We made sure we had lots of water: a gravity spring, a mountain stream, and a fast-flowing creek. In the old farmhouse, we installed an oil furnace that is gravity fed and doesn't need power from the grid to provide heat. We put in a wood stove to take advantage of the dead trees that had accumulated on our 25 acres over the past decade. A farm that had been neglected for years was a bonus because as vegetarians we wanted to raise food organically, and over time the chemical fertilizers and pesticides that may have been used would have leached out of the soil. Also the wild edibles that grew there naturally had had a chance to grow back. We quickly established an organic raised-bed garden to grow our own food.

From the then-published Homesteader News and a homesteading seminar presented in our home by Sherrie and Norm Lee, we had learned about growing the more hardy plants under plastic in the winter. Having appetites that included tomatoes and peppers, we also built a small lean-to greenhouse on the front of our farmhouse the first fall we lived on the property. The lean-to worked out well, providing solar heat to the house on cold days and using heat from the house on cold nights to provide a reasonably even temperature for growing finicky plants like tomatoes and peppers. We now have some plants that have lived for years. The lean-to location couldn't really be expanded to include what we were growing under plastic, so over the years, we decided to build a solar greenhouse.

Planning, Designing and Building a Recycled Greenhouse

As anyone who has lived on an average fixed retirement income knows, squeezing out money for capital improvements is a challenge. We had already built a two-story pole barn/workshop, so we decided we could build the greenhouse ourselves. We had a budget of $3,000 for a thermal greenhouse with an interior space of 400 square feet. As we drew our plans, it was soon clear that $3,000 was far short of the cost of materials alone. However, we weren't willing to compromise on some key requirements. The greenhouse had to provide essentially all of its own heating and cooling in an area where winters can get down to zero and summers up to 90 plus. Our lifestyle requires that we be away for days at a time, so we needed a design that was passive and could cope with loss of power. We had been active in local environmental projects since moving to our farm, so it occurred to us that many recycled materials can be used in construction, and that from time to time useful building materials are surplused at only part of their retail cost. The key idea for really low-cost construction that would meet our solar greenhouse needs came to us when we reviewed an old MOTHER EARTH News article on cordwood construction. We speculated that if most of the cordwood could be replaced with aluminum cans and plastic drink bottles to make a hollow wall that could be filled with plastic packing, we could have a super-insulated wall of great strength; and by filling the plastic bottles with water, we would have more thermal storage besides.

Having decided on the basic structural system, we quickly drew up the details. For maximum thermal gain at midwinter, the glazing angle was set to be perpendicular to the noon sun during January and February, making the glazing angle for our latitude 50 degrees rather than the 59 degrees that it would have been at the winter solstice. A spot was available in our little valley that was not in the shade at that time of year. Except for the southern exposure, there was to be no glazing in order to minimize heat loss on cold, dear nights. We did compromise by adding several windows to help with the summer ventilation. The pitch of the back roof was to be similar to one we had seen in Britenbush, Oregon; just enough that the top of the back wall would be heated by the sun in midwinter. This arrangement also shades some of the inside of the greenhouse in summer, reducing the summer heat load. We used space in the front wall and back roof for large swinging panels, activated by passive thermal actuators, to provide incoming and outgoing ventilation. We had seen similar large panels for ventilation in Acrosanti, Arizona, but the community had sufficient labor to operate the panels manually.

We designed the dimensions of our greenhouse for standard sizes of lumber: 16 feet along the slant of the front glazing, and 10 feet on the slant for the back roof rafters. We chose to place the greenhouse on the side of a small hill, allowing much of the lower wall to be bermed into the earth. A cross section of the plan shows that the use of bracing beams from the top of the back wall to the glazing support members requires no internal supports that might interfere with placing tables to hold the plants. The inside width ended up at 15 feet. The length was determined by what we could afford. The glazing we selected came most economically in six-foot modules. We settled on 29 feet of length on the inside. A key decision in the design was the selection of dual-surface polycarbonate glazing. While our goal had been to make this project a demonstration of the use of as much recycled material as possible, using surplused dual-pane glass panels for glazing, as we had done in our lean-to, proved impractical. We had misgivings about glass anyway, because several of the dual-pane glass panels we had used on our lean-to greenhouse had apparently lost their seals and fogged up. Also, we had experience installing doublepane glass and knew how heavy it was.

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