Bamboo Dome Tips

March 13th, 2009
Fuller's bamboo dome, composed of RR and RB crosses.

Fuller’s bamboo dome, composed of RR and RB crosses.

I’ve found many online references to Bucky Fuller’s bamboo dome design, but no reports of anybody actually building it.  Here’s my impressions, and a few things I learned.  (But keep in mind that my dome fell over.  Caveat Surfator.)

DESIGN: If you need a geodesic dome, this is a very good design in many ways.  It really is very easy to build and figure out, requires a minimum of math, wastes a minimum of materials, and you could make it with any fairly flexible poles, such as PVC or even conduit.   Because it’s a 5/8 dome, the wall areas are basically vertical, a nice feature.  Another nice feature is the ring of wide-open hegagons all around the perimeter — it’s easy to put an entrance on this dome, and that’s not always the case with geodesic domes.  It’s curvalicious, not pointy.  Most of all, it’s very satisfying to know that one person can build such a huge structure without any scaffold or special tools.  The ingredients were cheap — except for the tarps, strangely enough — so this dome would make decent post-apocalyptic refugee housing or meth-lab shelter.

However, the standard list of problems with domes certainly applies.  All your heat rises to the spot where nothing is.  Leaks abound.  Space is hard to subdivide or use.  Doors and windows are complicated.  And so on.  Before you decide round is the new square, please do yourself a favor and read “Domebuilder’s Blues”. They are fun to build, and have their uses — I think they’re great for public meeting places — but they are not good homes.

POLES: I learned the hard way: uniformity is key.  Use only one variety of bamboo, and try to get the poles all the same thickness.  Otherwise, stresses and bends will concentrate in the weakest areas.  A dome is only as strong as its weakest link; the shape loses a lot of strength with even one broken strut.

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POLE OVERLAP: Bucky glossed over this part — he gives all this math for the lengths of points BB, RR and RB, but for the amount of overlap between poles he says “about twelve inches” no matter the dome size.  Clearly this is not right for some domes — a 12″ diameter one, to use a silly example.  So how much overlap should there be, ideally? I mean, if you want to get all anal?

One way to do it is to keep the overlap to the minimum that will remain straight.  Finding that minimum is tricky — I think it has something to do with the diameter of your poles, and the amount of stress you expect.  But there isn’t much anti-straight force on the poles once the dome is built, so it’s less than you think.  Experimenting with two poles and some tape will give you a better answer than math, I think.

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My bamboo was really long, and I wanted to re-use it later.  So I decided to leave it uncut, figuring the excess length, lashed into the frame, would only make it stronger.  It did and it didn’t — it reduced the overall uniformity in a bad way, although it did give me some redundancy at the intersections that I liked.  There is definitely some way to leave the overlap so long that you end up with double bamboo on every part of the dome.  But you have to make sure you do that everywhere — see the note on uniformity, above.  Using stronger bamboo would be easier than all that.  But if the bamboo you have isn’t strong enough and you want to double it up, don’t do it with extra overlap.  Instead, make twice as many crosses and add them in nested pairs.

JOINTS: Duct tape worked wonderfully for the end-to-end parallel joints.  I suspect it wouldn’t age well, but for a temporary structure it’s the cat’s pyjamas.  It prevents any and all lateral movement, and it goes together fast.  Breaking it down isn’t too hard — you just slit between the poles with a matte knife or bamboo saw, and peel of the debris.  It’s not reuseable, alas, but it’s quick and snug.  For the intersecting joints of the crosses, duct tape is somewhat awkward, but works if you twist it.  A narrower strip of tape would be better.  Once the dome was built I realized that these intersection joints get hardly any lateral stress.  I overtaped them quite a bit, I think.

SKIN: Bucky completely skips this part, doesn’t he?  Skinning a dome is hard, any dome-owner will tell you.  We covered ours with a giant 40′ by 40′ tarp on top and four 12′ by 20′ tarps on the sides.  It leaked.  The top tarp was unwieldy to install, and sagged a lot.  In the Oregon winter, sagging tarps collect water, which weighs a lot.  That’s more or less what killed the dome.

If I do this again I will use smaller tarps and more of them, attaching them to the frame as it goes up, in some kind of clever geometric overlap pattern that I certainly haven’t figured out yet.  Also, I found that it was helpful to add a few more vertically-aligned poles across the largest hexagons of the top and sides, to prevent tarp sag in those areas.  If I do this again, I will add even more of those.  I also recommend a five-pointed star in the top pentagon, or some other peak to give drainage there.

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GLAMOUR: Be sure to take lots of pictures of your dome.  Put them on the internet!  People love pictures of domes.

6 Responses to “Bamboo Dome Tips”

  1. Arthur Says:

    The wind loads on a structure this size are going to be considerable. I don’t know if you get 30MPH winds up there in the winter, but if you do, you’re certainly talking several thousand pounds of force. If the structure isn’t anchored to guy lines in all directions, that wind load is going to distort the structure and transfer your nice, evenly distributed load onto one part of the structure.

    When they put up a small circus tent in downtown RWC, they drove a bunch of 2″ steel posts through the asphalt to anchor guy wires. You do the same thing on a smaller scale with a camping tent if you’re expecting wind. You’ve got yourself a really, really big camping tent.

    As far as preventing tarp sag, I think tension alone is going to be insufficent to keep water from standing on the flatter top of the dome. The closer to horizontal the tarp is, the more tension you need to put on it to keep it from sagging. As an exercise, try taking a largish tarp and four of your largest friends. Have them stand at the corners and pull as hard as they possibly can. Now sprinkle the tarp with a garden hose. (Do you like how I gave you the cushy job?) Can they keep the water from ponding on the tarp while keeping it nearly flat? How steep does it have to be before they can keep it from sagging?

    In my experience from pitching tarps for camping and music festivals, it’s nearly impossible to prevent water from pooling unless you have a significant slope AND a fair amount of tension.

    One way to achieve that in the dome might be to cap the flatter part with a cone or pyramid that sheds water easily.

    Anyway, even though I couldn’t make it to LIGHTBAR, I loved all the pictures. More Dome Pictures!

    Cheers,
    -Arthur

  2. Damage Says:

    Mykel,

    I wonder if you’ll be putting that dome up again at some point (before Halloween?) I’m a knotmaster/rigger and would be happy to help you tie the dome down, in exchange for the opportunity to DJ a Halloween Party there (complete with amazing morphing video by the Mad Doktor (maddoktor.com).

    Please do let me know! Am located in Portland within a mile of your location (I think).

    – D

  3. Damage Says:

    oops! sorry for mispelling your name! 😛

  4. Damage Says:

    P.S. – After I examined your photos, schematics, and choice of materials, I envision a custom-made rigging system specifically catered to your dome that is essentially “woven” throughout the structure for additional support and stability, with tie downs on the rope rigging structure so it doesn’t pull on the dome structure itself while preserving the open interior space. I anticipate at least 2 hours of constant work to rig it down “right”. We can also grommet the tarp if necessary in places and rig that into the rigging structure to keep it taut so it doesn’t take on additional weight.

    Please do contact me privately if/when you want help. I have alot of experience with setting up structures that stay put under many types of (adverse) conditions.

  5. mykle Says:

    Hi Damage,
    Thanks for the offer, but I don’t see myself building another dome any time soon. Nor do I have the bamboo on hand — much of this was destroyed in the collapse, so I’d have to go pick some more. I might take a year off from Lightbar, but my next structure will probably be a lighthouse.

    On the other hand, as you can see from this blog, building this dome is not so hard. A couple people should only need a couple days. Find yourself a spot and go for it!

  6. bamboo print Suegals Says:

    Interesting article, where did you get all the info from?

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