Formactive Geodesic Structures by Steve Miller
|In 1972 I first became interested in geodesic domes.
There was little information available at the time, beyond an article in
Popular Science for pool covers. A group of domebuilders in
California published Domebook 2 in 1972, which I bought right away
(Domebook 1 came out earlier, but must have been rare. I have never
seen a copy.). I studied it tirelessly, trying to get my mind around
figures based not on squares nor even with a gravity orientation.
That book was jammed with useful data; however, I was alarmed by the domes they were promoting. Although the geometry was a challenge for me, I had worked as a roofer during summers in high school and college, with shingles and flashing and roofing cement, and knew a lot more about roofing than anyone in Domebook 2 seemed to know. They were building hemispherical walls, with open seams facing the sky, and trying to seal them with new plastic products. They were working with inadequate budgets, and third rate materials, and making skylights out of vinyl. (It is important to understand that though domes can be made with a small amount of material compared to other methods, the materials must be of high quality). The only geodesic domes that had a chance were the offbeat metal and concrete domes that the writer/builders themselves condemned for their lack of aesthetic appeal. Aesthetics played a primary role in these domes. The builders were obviously artists; the book was a tour de force of creative domebuilding, covering a surprising amount of ground. Many domebuilders of today were inspired by this book.
The design they were promoting, with dimension lumber frames and sheathed with cut out, nailed on plywood triangles, is still the most popular residential geodesic dome type, made with the figures printed in that old Popular Science article for the pool covers. The domes built today for homes are mostly refined versions of the leaky hemispherical walls of the early days, utterly dependent on composite shingles to shed water.
In the back of Domebook 2 was a list of Fuller's geodesic patents. A few years later I sent for several of them, and was thrilled by the brilliance of the methods described. The ideas laid down in the patents were being ignored. The "Self-Strutted Geodesic Plydome" grabbed me. I had worked with plywood in the building trades, and had felt the strength potential in thin, bent plywood, although I had not thought of how to exploit it very well. The pictures of plydomes in The Dymaxion World of Buckminster Fuller showed domes made of full sheets of quarter inch plywood bolted together in an overlapping "shingle" pattern that got me going on a research project that started in 1981, and continued until recently, when I and my family moved into one. The overlapping plywood sheets make domes that shed water as soon as the dome is assembled. The basic building is inherently watershedding, and no shingles are needed. The tensional continuity is nearly perfect, unlike the primitive nailing on of plywood triangles. The shell is so strong that often no frame is needed; I have found a hex-pent frame to be advisable on my larger diameter plydomes, fastened on the inside after assembly. A hex- pent frame has 1/3 as many struts as a triangulated frame, and is used to increase rigidity. It is also handy for stapling on bubblepack insulation.
I found out that working from a patent can be a risky business- the plydome patent was a minefield for me. The domes I built were quite daring. I wanted to know just how strong a dome had to be to be useful, and wanted to accentuate the tensile qualities, which are beautifully described in Synergetics 1, in the context of balloons (Section 760.00). When my largest dome was in a state of partial collapse from a sudden heavy snow load, and I was jacking the undamaged section out, I thought of a simple mathematical formula to link geodesics to pneumatics. Fuller mentioned the usefulness of 'failure point research' in getting past the excessive overbuilding and compressive, crystalline structuring that plagues geodesic construction. I ran with that idea, and deliberately made domes that could possibly collapse. Then I carefully added supplemental structuring to bring them to usefulness, when possible. Some of them never got that far.
Almost all of my load testing has been with snowfalls. The 42' dome weighed about 2 tons and after a 30" snowfall was carrying 10 tons of snow. That was before I installed a thin 2v frame within the 6v dome in the hopes it could bear a 5' load someday.
Insulating in our plydome home followed a similar failure point pattern, where I am using an experimental approach based on tight sealing and air chambers within the ideal aerodynamic shape, with thoughtful use of vents. While experimenting with domes the most frequent question posed to me was, "how will you insulate them?" I studied the patents for the Dymaxion Deployment Unit, the Dymaxion Dwelling Machine, and the Fly's Eye (Critical Path) to understand the Bucky Fuller approach. The method I came up with is most like the postwar Dwelling Machine design (1940's) which used tightly sealed chambers with a rubber curtain hanging inside the airspace. Metal connectors are minimal, and fastened in wood frames. The rubber curtains are updated to 5/16 aluminized bubblepack (Reflectix). Although the bottom part of the house is unfinished- the insulation shows, and so it lacks the important inside air chamber in the lower 3/8 of the sphere- but our house is using an exceptionally small amount of fuel in the winter in Vermont, just a few gallons a day. This is with an R value of less than 10. In the summer we have no trees to shade the house, and a full exposure all year. The metal ventilator works as a parasol to keep sun off the top of the dome, and a rope operated trap door in the top of the ceiling enables air movement in and out of the top of the dome. This has been perfectly satisfactory for 3 years.
So far our plydome is working well. I am not offering it as a kit or plans, since I am not an engineer and doubt any engineer would endorse my designs- meaning building codes will find them unacceptable. Also, the process is familiar to me after years of practice, but would be a difficult process for the beginner to attempt.