Garden Dome
By John N. Hait Lesson
16
How can a knowledge of geometry allow you to build the largest shelter for the least amount of money? A sphere has the smallest surface area for a given cross section.
For example, a 20' x 20' square building has a roof area (and also floor area) of 400 square feet. If you add in the area of the walls, you must buy enough materials to cover 1040 square feet. In conventional construction with 2 x 4 walls, roof trusses, sheet-metal roofing, paint, nails, and a bunch of other stuff, even without counting labor, you're looking at a sizeable expense and a lot of work!
However, if we use a combination of natural materials and natural shapes we can produce a nice shelter, suitable for a patio or garden for much much less. We'll call it a "Garden Dome". A simple circular geodesic frame, as shown, covers the same floor area while requiring only 69% of the wall/roof area.
A round floor of the same size would have a radius of about 11'-3½" (feet & inches.)
The Dome consists of:
- A frame made with only 50 pressure-treated 2 x 2 struts. (Bamboo will also work if it is soaked under sea water for a week or more to kill the bugs inside. Then the ends have to be prepared to hold the eye-screws.)
- 100 eye-screws, such as are used to hang a false ceiling.
- 16, 2"-long bolts to go through the eye-screws at the hubs plus double nuts.
- Five ground anchors of painted rebar.
- And 726 sq. ft. of chicken wire (galvanized wire netting) or discarded fishnet.
- 750 sq. ft. of 4-mil. plastic sheeting.
Assemble the struts first. Eye-screws are bent 19 degrees at the top of their threads. Each strut has an eye-screws in each end. The length of the struts are measured from one eye-screw hole to the other. There are 30 (A) struts 7'- 2 13/16" long, placed inside the pentagons. And 20 (B) struts, each 8'- 11/16" long. It's important that the lengths be precise.
Then assemble the dome frame by connecting the struts together at each hub using a 2" bolt. Don't tighten the nuts all the way until the frame is complete. Start at the top of the Dome connecting 5 (A) size struts. Raise the dome step by step as you add the lower struts as in the picture.
When the dome frame is complete, tighten the nuts. Then tie the frame securely to the ground anchors at each of the bottom hubs. Otherwise, when the wind blows, the frame will actually walk away until it trips over something.
To catch rain water, hang plastic sheeting over the frame first, leave it somewhat loose so it won't be torn by the chicken wire. Eventually, the vines will keep the plastic out of the Sun so it will last longer.
Stretch the chicken-wire (wire netting) or fish net over the top of the whole frame. (Don't fall of the latter! And don't climb on the dome. It's not made to hold you.) For the short term, you can attach palm leaves or the like, to the wire netting like shingles in the traditional manner. It looks better, and helps protect the plastic.
Plant rapidly growing vines all around the periphery of the dome, except at the entrances. The vines will keep it cool inside, providing a practical, inexpensive roof, that replaces itself after a storm.
This is called a "Garden Dome" because it is not meant to be a house, although you can obviously add those things needed to make it into a house. However, do not cut any of the struts. The building is designed to use minimum materials, and every strut is vital. So, if you don't like ducking to get in, you can lower the floor at the entrance, or you can make a bigger dome by simply multiplying the strut lengths by some constant.
A Garden Dome, in your garden, backyard or patio, provides a convenient trellis for growing large-leaf vegetables, plus a nice place to relax during a hot day.
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Now that's exciting, isn't it!
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