Geodesic Dome Covering Assembly

This picture shows the basic plan, shown in a wormseye view without any shingling overhangs. The biggest piece (A/cyan) covers the top, plus one triangle on the bottom layer. The medium sized B/blue piece covers one whole side of the dome. The other small pieces cover the bottom ring of triangles. Conceptually, it's four parallellogram pieces of three triangles each, plus a door triangle (D/black). But the geometry of the A tarp lets it cover one of those bottom triangles, so one of the bottom pieces (E/green) only covers a two-triangle strip. Two of the parallellograms are (G/white, C/yellow) short-side up, one (F/red) is long-side up.

Here's more pictures, showing a walk around the structure from the sides, and then a birdeye view:

• Top Piece (A/cyan)
  Note that the overhangs are at least a foot everywhere, and they're all more or less horizontal. The hole at the top allows airflow, critical in the playa heat. (The plastic rain hat isn't up yet in these pictures.)
  

• Side Piece (B/blue)
  The big side piece covers 12 triangles, and the bottom is lashed down permanently. (As opposed to the smaller bottom-row pieces, which are often rolled up for ventilation.)
  

• Bottom-Row Pieces

  This is one of the top-short trapezoids (G/white):
  

  Here's side piece C/yellow, the one closest to B/blue, before and after taking down the top tarp. In both pictures it's partially taken down itself.
  

• Whole Thing

  Finally, here's a few shots of the whole thing before covering with tarps,
  

  and after. You can make a simple door triangle, which can either be tied back out of the way or tied shut when you're asleep or gone.
  

We used tarp holders to secure the tarp to the vertices, since they don't create holes in the tarp that would let in rain like metal grommets. They're blue plastic thingies that you can buy in outdoor stores. We loop a cabletie through the hole in the tab to lash it to a vertex.

The problem with these tarpholders is that they will pop out when they're under too much load. Grip Clips instead, which I might try next year. The Grip Clips are also easier to position,

This schematic diagram shows the location of the tarpholders. The key idea is to create tension to minimize tarp flapping, both because the sound is annoying and because uncontrolled flapping gets worse and worse as the wind tears the covering apart. On the big top tarp, the first set of holders goes right below the top pentagon. We also use holders along the bottom row instead of just lashing with metal grommets so that we can have the rain-proof overhang. The only nonobvious thing about the side tarp is the holder in the middle of the center bottom triangle, which is there to secure a fold necessary to fit the rectangular tarp to the spherical curvature of the dome.

You should tie down the tarp overhangs at many points, roughly every few feet, using strategically placed grommets. I used 75-pound-test nylon parachute cord, which worked fine. You tie a grommet on top to some spot on the bottom ring of horizontal struts. The best tie-down point is a vertex, since that can give you both horizontal and vertical tension. In some places, when you only need vertical tension, you can just tie it directly to a strut.

You should loop the cord under the strut so that you can get leverage by pulling up tight against it. Tie them as tight as you can, but keep in mind that you'll probably want to go around and tighten them all up every few days or so and during major windstorms, so don't make knots that will be too difficult to take out. I just used triple half-hitches.

Keep in mind that you'll want to keep some triangles completely clear of tie-down cords so that you can easily get in and out. We had an official door triangle, but also used two or three others as main access passages when some of the bottom triangles were tucked out of the way for airflow and visibility.

The long parachute cords are tiedowns for the big overhead tarps, since there's a long distance between them and the bottom ring of struts, and they're intended to always stay tied down. The bottom strip of tarps is different: you want to have the option to move some of them up out of the way for airflow. The tops of those strips are secured to the chest-level struts with cable ties, just like the big overhead tarps. We used two-sided velcro instead of cord for most of the strip bottoms and sides, so that we can quickly fold an entire triangle out of the way. (The bottom strips are also not under nearly as much wind load as the big overhead tarps, since they're smaller, lighter, and more sheltered.) In the picture below, you can't see the velcro strips in this picture shot from the inside, but you can see how a triangle is folded out of the way.

The hat worked fine in 1999, but in the major rainstorms of 2000 there was a minor leak because the washer setup was not waterproof. Next year we'll try using O-rings at that spot. (The other main strut vertices don't have to be waterproof, since they're covered by tarps. These are the only ones exposed directly to rain.)

I don't have as many details here as for the strut assembly, but here's a few:

1. Wrap the top five vertices to keep the sharp struts from abrading the tarps at these points where it's going to be under tension. The first year we didn't do this, and halfway through the week we patched the worn-through tarp with duct tape and stuffed towel scraps on the vertices. This year I'm going to try wrapping the struts with chamois tape - the stuff that you can buy at sporting goods stores to wrap around the handle of a tennis racket.
   

2. You want to put up the big piece first. If you already have the long tie-down strings in the grommets, your life will be much easier, since you can use them to gradually pull the tarp up over the structure. Although it's almost impossible to put up this big tarp alone without the strings, it's quite possible with them. Pull each clump of two or three strings up as far as feasible and temporarily tie them off. By the time you do this with all of them, you can cycle back to the first clump and hitch it up further. It took me a couple of (leisurely) hours to get the whole thing in the right spot. With several people that will go much faster, less than a half-hour. If at all possible avoid putting this tarp up in high winds.
   

3. It's much easier to get the tie-down cord under the bottom ring of struts if you do it before hammering down the anchors.

4. We used one big 20x20 square tarp as a ground tarp that we just folded underneath itself to make it into a roughly 18-foot circle. The way to keep the inside dry during rains is to make sure that the ground tarp is smaller than the covered area, with a foot or two of space between the tarp and the outer ring of the struts so that the tarp always stays completely dry. Otherwise, if the ground tarp comes all the way up to the outer covering, or worse yet extends outside of it, rain that ends up on the outside fringe of the ground tarp will inevitably make its way to the middle.

   The first year we were pretty dogmatic about taking shoes off on the way into the dome, which was a pain to do. The second year we were more lax (except when it was muddy), and just swept the ground tarp clean more often.

   A note on disassembly: just fold up the ground tarp and then shake it out back in civilization, where random little bits of food-gunk will biodegrade. Don't shake it out on the playa! (Also, don't forget to shake it out before going back the next year - we forgot about this and had to painstakingly clean it up with brooms when we got back to the playa in 2000, which was a drag.)

5. You can't put the rain hat up until after the big tarp (A/cyan) is up, and we needed two people to do it (at least with the size ladder we had). You first attach the top of the mini-struts to the hat, and tighten them up. You can pre-load the bolt assembly on the bottom of the mini-struts, but don't tighten anything.

   Our ladder was just tall enough that one person could fit their arm through the air hole, but not their head. The second person needed to stand on the outside and throw the hat into the hand of the first person like a frisbee, being careful to keep the struts facing up. (You want the smooth plastic side of the hat to be touching the tarp, not the sharp strut ends which could tear it.)

   The ladder person needs to catch the hat blind, which is doable with enough tries and yelling. Then the ladder person can turn the hat upside-down and position it so that the bottom of the mini-struts line up with the holes in the three main struts. For each mini-strut, undo the bottom washer and nut, thread the bolt through, re-fasten the bottom washer and nut, and tighten it up.

• Each Triangle

  If we didn't care about rainproofing, by far the easiest thing to do would be to have 40 triangular tarp pieces, one for each triangle. That would be simple to make, since there are only two kinds of triangles: 10 equilaterals with long (cyan) sides, 30 isoceles (with two long, one short sides). This design would work fine for shade, but rain would drip in at all the seams. Shingling doesn't work: just having some overhang between the faces isn't enough, gravity works against us on all the non-horizontal seams.

• Parachute

  We vaguely thought about using a parachute since the curvature would be close to what we needed. But we didn't think they were rainproof, we couldn't find one at any nearby surplus store, and some of the ones we saw on the web were really expensive.

• Single Giant Tarp

  Another possibility would be to cover the whole dome with one huge tarp, say 40'x40'. Problems: that much tarp is really heavy (70 lbs) and hard to deal with, especially in high winds. It's hard to find tarps that big, our local stores only had up to 20'x20' or 18'x24', and they're very expensive. We still would have had to do some amount of cutting and grommeting to deal with the curvature. It would have been harder to deal with rolling up the tarp covering the lowest ring of triangles for airflow, since there would be a lot of overlap because of the curvature of the dome.

• Tarp Type

  We tried out the blue normal tarps, but found that they just weren't strong enough. The silver heavy-duty ones are definitely necessary for this kind of structure. Even with these we had some problems with the sharp edges of the struts wearing away the tarp at the vertices where they're under tension last year. This year we're padding with chamois tape (the kind that you wind on the handles of tennis rackets) to try to avoid that problem, in addition to reinforcing key points with duct tape.