Passive Solar Greenhouse Plans_02
Researched and written by Jim Thomas
Every garden in northern Arizona contains our native sunflowers.
The previous essay describes my motivation and research into how I might solve this challenge within my limited means. Picture number one (previous page) shows my first actual experiment implemented during my research. This was as simple as it gets! I purchased several blue Styrofoam building boards from the hardware store along with a tube of silicon glue. With a box-cutting knife I hand-cut the pieces and glued them into a simple box with no bottom and a top opening slanted at 45 degrees. The size of this Styrofoam box was determined by the available panel of glass I used as the lid, in this case a recycled shower door. Pictures 02 and 03 (previous page) indicated the level of detail I managed to achieve in virtual reality using just software. These renderings even gave me some insight into how sunlight was going to interact with the walls. This was important to be aware of even in this early stage of construction. Picture 19, for example, shows where the sun’s shadow from my fence hits my grow frame on December 21st, the shortest day of the year. I had been observing this shadow line for years prior to taking on this project. The height of the bottom wall of my grow frame was based completely upon this realization.
As you plan your own growing structures, know in advance where the shadows in winter fall. Stake them out or mark them in some way so you’ll know in another part of the year when you are building just where your sunlight edges will be.
Measurements
This brings up the subject of my measurements. I’ve shared these plans and photos with many people. In fact, on several occasions, the entire local Master Gardening class run by the University of Arizona comes by for an inspection and sooner or later this question comes up. “How did you determine the width, the height, or the angle of the glass?” The intent behind the question always seems to be the desire to run home and duplicate it, like a boat or a shed blueprint.
I didn’t plan it that way. Remember, I wanted to design a construction that used as few tools as possible. Planning was more important than complicated assembly. Everything was pragmatic. It is easier to cut a wooden guard rail than a cement brick. So, the depth and length of the bottom of the grow box was determined by simple combinations of available cement bricks. I laid them on the ground and measured them, six in a row, seven in a row, and so forth. I reproduced these measurements in my computer drawing and when I had the right combination that also matched my existing glass doors, set three across, I proceeded.
ALL essential measurements of this structure were determined by this method of pragmatism. Where is the sunlight? Where are the shadows in winter? What are my building materials. How big is each item? How easy is it to cut? What are my tools? Hopefully this explains why my plans, as I call them, are absent of the typical blueprint kind of diagrams. Your project will be determined by what you use. If your bricks are a different size then ALL of your measurements will be different from mine. If you use old windows instead of shower doors then everything will be different. I’ve presented this with as many actual photos as possible, as inspiration rather than as a blueprint. You’ll have to exercise some on-site problem solving skills. No one blueprint plan would apply to every situation.
tep by Step
Photos 04 through 08 verify that I followed my computer drawing plans exactly. Figure 04 shows that I actually clamped a brick to a piece of foam board and used it as a measuring device. How basic is that? Figures 05 and 06 show the finished grow box in place replicating my 3D drawing exactly. This was very rewarding to see in reality. Figure 08 shows the first steps toward building the upper half that supports the glass and collects the heated light. In the background of this photo you can see another extended growing season device that attracts just as much attention during on-site visits. In my impatience to do some gardening while I built my grow frame I quickly built this screened-in semi-solar grow area. First, you have to be aware that I live near open fields filled with grasshoppers, at least five different species. They find my backyard within days of any fresh vegetables sprouting from the ground. Initially this gardening space didn’t have the protective screen, but one afternoon I actually watched an entire planting of vegetables disappear before my eyes as a result of voracious grasshoppers. Over one weekend I framed and screened in the entire area, much to their frustration. Picture 08 shows the structure with all of the shower doors in place. Even this much of a glass surface in spite of all that open screened area (not air tight) created a microclimate gathering extra warmth and being a shelter from the wind. To this day I grow things in this space for six months or more of the year. Picture 09 shows a successful zucchini plant and Picture 10 verifies that I’ve even grown corn inside this space! The glass doors are all removed in Picture 10 for watering and weeding.
To return to my step by step descriptions. Another difference between Picture 07 and Picture 08 is the fact that I’ve filled in the wood framework solid with layers of blue Styrofoam. These insulation panels were simply cut and glued into place. There are four layers of one-inch-thick foam in each wall. Three layers fit within the small studs and an additional layer was glued inside the structure. You’ll notice that the entire interior was painted twice with very opaque white paint. This protected the foam from water and ultraviolet rays (which eat Styrofoam) and enhanced the light collecting ability of the grow box.
Figure 11 shows how I cut several short pieces of cedar (originally 2” x 3”s) at 45° to match the angle of the sides. This allowed me to develop a faceplate that sat flush and was airtight. This would later hold all my glass panels and screens as I manage them according to the weather. Picture 13 shows the grow frame complete except for exterior wood paneling and a couple coats of white paint inside. Picture 12, taken later, shows the final layer of glued-in Styrofoam paneling which completed the insulation, now four layers thick in all three walls.
Step by Step
Another major consideration in every greenhouse construction: The north wall. One of the weaknesses of most greenhouses in a cold climate is the cold north wall. It is the biggest source of cold and loss of stored heat in a free-standing structure. There’s no such thing as too much insulation on the north wall. This explains why a pit greenhouse or a greenhouse with a large dirt mound against the north wall is so successful. These solutions keep the cold away from the north wall. In my case my insulated, and internally heated, home south wall was my backdrop. This alone guaranteed a certain amount of passive success. Give this subject lots of serious thought as you make your plans. It will be easy to heat any grow frame or greenhouse in northern Arizona because of our combined altitude and latitude. Keeping the heat overnight will be the challenge! This concept and the principles that make an insulated grow frame work are illustrated and explained in deeper detail in my article, “From Cold Frame to Grow Frame,” in the Solstice Report Issue Two. It seems simple but most greenhouses I visit fall short and must be cooled or heated in order to keep their plants alive. I have a friend who invested over ten thousand dollars in a purchased greenhouse, with double glazing and an 800-gallon water tank for mass storage. In the winter he must still run an electric heater all the time to avoid freezing, simply because the structure is 100% glazed and the collected heat can escape just as fast as it was gathered. It’s a wonderful structure but a failure in terms of being passive. Management of the internal environment is mandatory and the secret to success.
Picture 14 indicates the base beneath a platform I installed in the grow box before filling it with soil. I covered these with some of the cement blocks I used in the walls. This provides me with a place to stand or squat while I plant, weed or harvest. Picture 15 shows clamps holding wood rails as they dry (everything was glued and screwed) that act as guides for my glass panels and screens when they are in place. Picture 16 is the nearly finished grow frame. All it lacked here was the exterior wood paneling, which I added the next Spring. You can see the front supports that hold the glass doors are removable providing me with a totally open structure when I want to work on the soil, do maintenance, chase pests or add a trellis.
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