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A PA Sunpit Bioshelter: our second Pennsylvania bioshelter by Dawn Shiner, MSc, and Frank M. Hyldahl
Project Goals:
To design and construct for homestead and farmstead use a simple, affordable, appropriately-scaled, passive-solar season extender for maximum termperature stability that would provide Winter greens and Spring seedlings.
Guiding Project Criteria
The Results: 
PICTURE 1: February snow insulating closed-up Hot Frame. Sunpit bioshelter door about to be closed. PICTURE 2: Winter Greens, December PICTURE 3: Winter Parsley, Tatsoi, Violas, Celery PICTURE 4: Thermal Energy from Creeping Thyme benches melting snow. PICTURE 5: Winter SE corner, Typhon Holland Dutch Greens and New Zealand Spinach This Sunpit Bioshelter represents resiliency and survival appropriately-scaled to be affordable, do-able, and simple to maintain.  PICTURE 6. Frank and Dawn's PA Pit Bioshelter. Situated on a 10% South-facing slope in Northwestern Pennsylvania's Zone 5, this unheated structure provided 132 square feet of year-round diversity of edible greens for a family of six, supplied potted cherry tomatoes and specialty peppers for Christmas presents, and grew celery and petunias year-round with the interior use of floating row covers.
Glossary: A bioshelter is a solar greenhouse managed as an indoor ecosystem. All parts are connected and working for the good of the whole, all systems. For more information, Wikipedia. A sunpit is a solar greenhouse that uses the earth's thermal mass to make a beneficial thermal environment for plants. For more information, Google
THIS PROJECT combines the best of both bioshelter and sunpit research, from the first American shadehouses to the wave of bioshelters stimulated by the founders of New Alchemy Institute and our grounded experience with the fourth US bioshelter grant project combined with our love of hot frames and microclimates. Meeting the Project Goals Simple ~local hay bale resources ~sifted on-site subsoil (durability tests: portland cement with and without lime) ~recycled scraps of wood, electrical fence wire, chicken wire ~intermittent, meditative labor fitting in with family
Affordable Passive solar ~facing true South, ~angle of incidence for glazing set for Winter and Equinoxes ~132 square feet of deep growing beds ~absorption, reflection, and convection for temperature stability ~seed and herb drying space
Thermal mass temperature stability ~haybale North wall provided insulation and thermal mass with parge overlay. (The extra cost of straw versus hay for the extra thermal gain from the hollow cores was deemed unnecessary.) ~4-foot deep and 2-foot wide trenched pathway reradiating solar heat and 57 degree F earth temperature into the evening, ~¼ gallon water containers lining edges of soil and glazing.
Appropriately-scaled ~nooked into a 10% sloped hillside with a foyer for Winter access, ~15.5 feet x 8.5 feet with a truss drying loft, ~East Window ventilation and protected West door ventilation, ~Habitat development inside and outside door and window.
Maximum termperature stability ~microclimate of midNorth bed most stable, ~able to grow greens for daily meals and celery through winter, ~petunias blooming under row cover, primroses for color, violas for amendments, ~self seeding for spring garden transplants (lettuce, asian greens like tatsoi, etc.), ~continuous deep beds for temperature, soil life integrity and integrated nutrient management. ~went from putting a second layer of plastic below the trusses on the inside of the sunpit bioshelter to using floating row covers directly over the planting beds.
Homestead and farmstead user-friendly ~scaled for easy maintenance, ~easy set up for self-sowing, reseeding system giving Spring greens and transplants. ~able to afford more than one...one for winter greens and spring transplants, one for bottom heated flowers and tenders, one for perennials and overwintering species, one attached to the house,...
Winter greens and Spring seedlings ~midNorth growing bed most stable in temperature ~able to grow celery through the winter in the center of the North growing bed, ~able to grow cherry tomatoes and holiday peppers for Christmas presents ~eat greens for a family of six with company every three or four days--from even the coldest South bed until the plants began growing again in February. (A testament to our timing with plant maturity, our canning or drying skills, and the resilient qualities of the structure.) Greens are being harvested but not in growth mode in December, January and beginning of February. ~petunias continued to bloom under floating row covers in the center of the East bed once small containers (½ gallon) filled with water at the glazing edges were added.
We highly recommend the simplicity of this pit bioshelter. It can be free standing with a haybale or strawbale North Wall, it can be on a slope or not, and it can be attached to a dwelling for even more stability and heat. There have been pit greenhouses dug out completely with tables instead of deep growing beds and even side composting chambers. One pit had manure spread under the entire greenhouse floor, but only was used for one season. So many ways one can play with natural laws and work with nature.
If you're interested in self-empowerment, here's what we did.
Our first year projects were to establish a garden by sheet mulching, start smother mulching the North face integrated orchard area, and construct a hot frame for the Spring seedlings.
PICTURE 4: Second Spring. Hot frame in sheet-mulched garden. (Rock center-left denotes garden center.) Note mock-up truss for pit bioshelter on hillside.
Second year after the garden was in full swing, Frank began carving out the hillside. The topsoil was carefully saved. In a dance of elegant respect with the water level, carpenter's level, flat-bottomed shovel, post-hole digger and various levers, all was deftly moved, along with the rock that became the center of the circular garden.
Sifted subsoil from the pit was tested for compatability with the portland cement as a parge for the haybale walls. Overwintering varying ratios of silty subsoil and portland cement with or without additional lime showed more durability without lime. (Such is the functional beauty of site specific research observations.) The below Plan View of the Sunpit Bioshelter shows the North wall and U-shaped growing space with its sloped portion. Inside dimensions of 15.5 feet x 8.5 feet for this structure provided us with 132 square feet of connected, deep-bed growing space, plus another 31 square feet of vertical North Wall space.
DRAWING 1. Plan View
Preparing the site, meant leveling most of the growing bed area and digging out the 4-foot deep, 2-foot wide accessway to the U-shaped growing bed. The dotted lines at the end of the accessway denote two earthen steps. In the coldest part of the winter, two 5-gallon buckets of water would sit there to aid the temperature stability with the extra heat given off during phase changes.
As with strawbale wall construction, haybales for the North wall were stacked in courses two or three high. Added stability and more interior space were gained by stacking the bales on end. All sills and haybales rested on EPS board resting on flat sculpted ground. The courses of haybales were kept rigid on both ends by boards. Bales and boards were horizontally wrapped and tightened with leftover electrical fence wire and tighteners. To keep the wall from bowing, wires penetrated the bales connecting the inside and outside horizontally-wrapped wires. A utilitarian needle was made by pounding one end of a bicycle spoke and drilling a hole for "threading" the wire.
The drawing below shows the elevation view of the North haybale wall with a plan view of the framing on the haybale tops.  DRAWING 2. North Wall Elevation PICTURE 5. North Haybale Wall ready to parge.
| Here we have our 4-year-old prime contractor examining the wire wrapping on the haybale courses. Using strawbale techniques for the creation of the haybale North wall, the haybales were stacked on their narrower edge to gain more height and interior space. This also added stability to the wall as the ends of the hay meshed together. (For a higher or more load bearing wall, we would have used cement between the bales for more stiffness.) PICTURE 6. North haybale wall unparged. |
Tent poles, conduit and rebar were inserted in the bales for more verticle stability. (For such a small structure with such a light load, this stabilization felt good, but in reality was little needed.) The haybales were set atop 2" EPS board to preclude the bales from touching the ground and wicking water from the earth. No tarpaper splash guarded was used under the outside parged North wall.
Leftover electrical fencing wire was used to horizontally wrap the bales which were braced on the East and West ends by 2 lengths of 2"x10" recycled boards. To keep the wall from curving, electrical fence wire was also wired through the bales connecting the wires on the interior and exterior of the bales. (A bicycle spoke was used as a needle, having one end flattened with a hole drilled for the eye.) Parging the Sunpit. The sunpit parge was a combination of sifted sandy loam from our site subsoil and portland cement. Samples of various rations, some with lime, were tested over the previous winter. Our site specific ratio turned out to be 6 parts of sandy loam to 1 part portland cement and no lime. To hold the parge around the end supports, chicken wire was wrapped over tar paper. The parge was applied directly to the haybale fibers. (Having a misting setting for the hose was important to prevent the parge from drying too quickly in the sun.) Detail "A" below shows the end wall structure and framing to nail the roof trusses atop the haybales. DRAWING 2. End frame and roof trusses, Detail "A" 
DRAWING 3. Trusses and Gussets, Detail "B" | PICTURE 7. Interior Gussets and Rafters. Note experimental peat/portland cement trial insulation on the far right top of haybales. Roof insulation molds for "batter" to insert between roof rafters. 
|  PICTURE 8. One year we created a plastic roof under the trusses that indeed allowed cherry tomatoes to continue ripening after Christmas. |
The trusses fitted to this North wall rested their South face on EPS board as well. Trusses were constructed for roof and glazing support and designed for a 57 degree angle and an 8-foot lower truss chord. 
DRAWING 5. West Elevation of Pit Bioshelter, below
DRAWING 5. East Elevation of Pit Bioshelter, above The rafters served to dry seed heads and reseeding happened without effort. In the sloped bed, small terraces were made with pieces of slate. The premier microclimate conditions always germinated the first Spring seedlings. 
When we had to take down the Sunpit Bioshelter after two years of total neglect, leeks and euphorbia were still growing in the structure. 
The walls and structural integrity were solid, requiring sledge hammers. Sunpit Materials List (most everything) 18 bales of hay (for under $18 at $0.95/bale) 3-4x4x54" supports (bartered from sawyer) 2-2x10 end braces (recycled) 2 pcs of chicken wire fencing (leftover from neighbor) 95' of electric fence wire (leftover) 2 electrical fence tensioners (tightening 2 full courses) 2 bags of portland cement (purchased) 23' of 2" x 6" lengths along tops of bales (recycled) 14' of 1" x 4" cross pieces on these lengths as nailers (recycled) 18 wooden triangular gussets for nailers and trusses 2 metal gussets inside outer wooden gussets at the ends 9 trusses 2x4's x 8', 10' and less tha 8' for roof. (purchased) end roll of greenhouse glazing ($50)
Acknowledgements Grateful for an endearing book giving a historic overview of greenhouses as forcing, propagating, and storage structures and the evolution of sunpit greenhouses written by Kathryn S. Taylor and Edith W. Gregg called, Winter Flowers in Greenhouse and Sun-heated Pit, published by Charles Scribner and Sons in 1941 (revised 1969), grounded and inspired by our bioshelter research experience, Frank commenced construction of Dancing Green's first sunpit structure in 1990.
Postscripts In our first bioshelter project at Three Sisters, the integrated systems used the heat and gases from the chickens with the heat and gases from the composting chambers pulled by solar fans through biotic filtering systems and blown through ducting into the rocks forming the base of several of the connected, raised, deep growing beds. The North wall composting chambers were filled and turned to give temperature stability to the growing space and provide bottom heat for the seedlings. The blocks that formed the connected, deep, growing beds had their cores filled with soil and provided habitat for beneficial insects as well as herbs and flowers for the salads grown in the deep beds for the Pittsburgh market. Microclimates were recognized and enhanced according to the seasons. Nutrient cycles were maintained with compost, green manures, herbal teas, and dynamic accumulators. As the fourth Ark-influenced Bioshelter in North America, we had lots of fun with this project. [YouTube connection to "A Pennsylvania Bioshelter".]
Lessons Learned Our grant proposal for this bioshelter appealed to the Pennsylvania Energy Office's need to address the nitrogen runoff from undecomposed manure affecting the Cheasapeake Bay. However, the bureaucracy of the PEO grant process stretched the original bioshelter design from a reasonably-scaled solution through a solar architect who produced an expensive, though impressive, structure that cost more than an average farmer could afford or need pay for cost effective results. Not knowing the importance of holding the scale to more doable, the government's enthusiasm with the promise of the project potential pushed us into an impressive showpiece that was not commonly reproducible.
We also came to see that for production purposes, smaller structures offered the potential of more microclimate control and ease in dealing with inbalances in pest/predator populations. By having more small scale structures interfacing with the environment, diversity in products (hardy to tender) and uses (seedlings to overwintering) could also more easily be addressed.
Our research proved the above true. By scale alone, the extremes of temperature fluctuations were more simply modified by the soil and stucco/haybale thermal mass and the thermal phases of the freezing and unfreezing small water containers. As another plus benefit, we found ourselves using the rafters to put seedheads to dry and finding ourselves managing a reseeding greenhouse whose reflective slate pieces (used to create micro-terraces on the sloped North bed) created microclimates within the greenhouse microclimate.
Destruction of this Sunpit Bioshelter was mandated with the sale of the land. At that time, the Bioshelter had not been tended for three years. We returned to surviving leeks and with tears sledge hammered a ten-year-old stuccoed haybale wall into pieces. You could see the one spot the wall had absorbed moisture before I used slate pieces to hold the topsoil away from the stucco...about an inch by four was discolored and slightly decomposed. Otherwise the wall (which was never sealed on top) was intact and would in our estimation have lasted years and years longer; a good forty to sixty to ninety!
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