Solar Heated Chicken Coop

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The basic concepts behind the construction of a solar-tempered chicken coop have been known and used for a long time. Most traditional poultry houses have lots of windows (mostly for light rather than heat), and early homesteaders' coops were often built low to the ground and of logs.

The primary solar features used in our coop are south-facing windows, thermal mass to store heat, and outside insulation and insulated window panels to keep that heat in.

SITING: Since the coop could be dry inside only if the building site was high and dry, we dug several test holes a foot or so deeper than the planned excavation, and checked them later to be sure no water had seeped in. Then, to ensure maximum solar efficiency, we checked the site for both morning and afternoon shading problems. In our case, we settled on a sort of compromise -- direct sunshine from dawn until about 4 pm when, in the summer only, the leaves of an adjacent woodlot (maples, birch, and basswood) provide partial shade for the coop.

EXCAVATION: The dimensions of our coop were determined by estimating the size flock we wanted (20) and multiplying that number by four square feet per bird. As it turned out, eight-foot-long interior walls, using a five-sided shape, yielded a floor area of 85 square feet. Since our foundation logs averaged eight to twelve inches in diameter, we staked out the site a couple of feet larger than the interior dimensions. The edges of the pit were cut as vertically as possible, and most of the dirt was piled on the north side.

FOUNDATION LOG WALLS: When the excavation was about three feet deep and the bottom leveled, it was time to begin laying the walls. The logs had been previously cut, peeled and sorted by size. The largest diameter poles, for the bottom tier, were notched on the top side with a chainsaw and axe (Fig. "a"), and subsequent logs were notched on both top and bottom (Fig. "b").

Each piece was laid temporarily in place until all adjacent logs were matched to it and irregularities between them removed with an axe or adz. Then the log was removed from the wall and coated on all surfaces with black waterproof roof sealer. If cedar, cypress, or treated poles has been used, this laborious step could be eliminated. But we used what we had -- Balm of Gilead, or Balsam Poplar.

When re-placed in the wall, the logs were secured at each end by a single "spike", actually a short (10 to 18 inch) length of 3/8 inch steel reinforcing rod. Care was taken to be sure that no spikes were placed where the door opening would later be cut. Logs were laid until a wall height slightly above the original ground level was reached.

Picture (Metafile)

FRAME UPPER STRUCTURE: To facilitate insulation of the above-ground portion of the structure, standard 2-by-4 frame construction was used. Only slight modifications were needed to accommodate the transition from logs to dimension lumber (Fig. "c"). Double vertical studs were placed in the middle of the two north walls and at their junction to provide support for the three stout maple rafter poles. Likewise, the midpoint and each end of the south wall were framed to support the other ends of the poles.

All openings were made to match the dimensions of the old windows and door we had scrounged up. Exterior wall boards were nailed on at this point to give rigidity to the structure while the roof was being put on.

ROOF AND WATERPROOF COVERING: The roofing job consisted of notching the three rafter poles, setting them in place, hacking off the most obnoxious upfacing knots, and nailing on roof boards. We tried to save the strongest, smoothest, and widest boards for the roof. Any sharp or ragged edges or knots which could have punctured the roof covering were planed or filed smooth. Roof and wall covering material was applied in one operation to avoid any possibility of leakage at a roof/wall seam.

We literally wrapped the entire building in roofing felt (tar paper scraps and roll ends left over from building our cabin). The purpose of this layer is not so much to provide a moisture barrier, but to protect the next layer - polyethylene film - from the roughness of the wood.

Next we carefully draped a single sheet of six-mil polyethylene over the whole building. The film extended from the bottom row of logs up over the edges of the walls, with all excess left temporarily on the roof. This extra material allowed the film to creep down along the walls during backfilling, without stretching or tearing.

Just before backfilling, several layers of foam boxes (salvaged from a cable tv company) were stacked up between the sheeting and logs. Our boxes tested out to have an "R" value of four, not including the insulating value of the air spaces inside and around them. An "R" factor of eight to ten should be adequate for this type of below-ground application.

Soft, clean sand was gently shoveled against the wall, the trench around the coop finally filled in. Straw bales were stacked against the north walls and around the east and west corners up the eaves' height and tapered away from the building to provide a smooth contour into the surrounding area. [See note at end concerning using straw for backfill.]

Foam boxes were arranged on the roof and then the whole thing, including surrounding bales, was covered with a few inches of light soil and a thick straw mulch. From the north, the coop looks like a rather casual pile of straw.

FINISHING TOUCHES: We put a little trim around the windows, doors, and the edge of the roof, nailed some cedar boards on the exposed exterior wall surfaces, and then the outside of the coop was finished.

Inside, fiberglass insulation (some of which was salvaged from old hot water heaters) was put into the walls, and interior wall boards were nailed up. A coat of paint (white on the upper board walls, dark brown on the lower log walls), roosts made from ironwood saplings, nest boxes hung on the wall, and a pickup load of dry, coarse sawdust completed the project.

During the winter, we added an insulated panel to cover the front window and to help retain both heat absorbed by the dark-colored log walls during the day, and the significant amount of heat given off by the birds.

Well, that's all there is to it -- a couple of weeks of good, healthy exercise, a few dollars for materials we were unable to scrounge, a lot of fun . . . and the chickens love it.

Steve Schmeck

NOTE -- 1999: From Sue. The chickens made this coop their home from some eight years, and thrived. It worked well for them and for us. The chickens are now gone, but the coop still stands, twenty years later, and is well utilized as a garden shed. There is a leak in the roof now, and next summer we are going to unbury and strip the insulating boxes and plastic off to repair and recover the roof covering.

The early straw bales worked as backfill only until they started to break down, which of course they did, settling and exposing the upper part of the coop to the weather. We wrapped the exposed area in sheets of dark colored, closed-cell foam we had left from our house building, and told ourselves we'd get to properly burying the coop soon. Meantime, we piled brush and apple tree branches from pruning and trimming around the back of the coop to hide the ugly foam.

Well, soon does come sooner or later! And on the homestead, it is usually later. We did add some extra dirt around the coop some years ago, but not enough to reach the roof. The roof itself has a wonderful, living covering of moss and weeds living in its six or eight inches of dirt. We will be sorry to have to disturb that covering, but we plan on the building last at least another twenty years so the later will probably come soon, and the old chicken coop will finally get its new covering and dirt surround.