Introduction: 24 Foot, 3V Geodesic EMT Dome
In 2011, like many, many other desert goers, I built a geodesic dome for shelter from the sun, wind, and some of the dust to be found in the Black Rock Desert. At the time I found it exceedingly easy to find resources on how to calculate strut lengths, and how to build a dome skeleton from Electrical Conduit (EMT). There are many ways to do this; what I found simplest and least expensive was to flatten the ends of the EMT struts and drill holes so that at each vertex, one bolt would hold everything together. There are more labor intensive and expensive methods that leave you with a nicer and/or easier to assemble final product, but this type of construction I found to make the most sense, and indeed it seems to be the most popular method.
What I found a little more difficult to come by were detailed accounts of how to make a cover, how to get a dome cover of this size on and off by myself, in the wind. How to make a door, and people's experiences with actually setting up and tearing down something like this alone. I'll try to share my experiences in as much detail as I can to help future dome builders decide on their own method.
Step 1: Materials
Because of the way I've written this instructable, it's very difficult to proscribe a particular material list. As such this list is less of a bill of materials, and more of a list of things you'll need to think about how to do, where to get, and so on.
Strut material - I used 3/4" EMT (Electrical Metallic Conduit). This is available at Home Depot, Hardware stores, and electrical supply houses.
Canopy fabric - You have many options - see the section below on selecting a canopy. I used recycled billboard fabric I got for free from advertising agencies and through craigslist want-ads I posted.
Stakes - If you're doing this for Burning Man or any other desert festival, you should already know that stakes are of the utmost importance. I will discuss these in detail later on - at first I used 2 foot rebar "candycanes" and in later years switched over to 18" lag screws.
Hardware - You'll need to fasten the struts together somehow. I used 5/16" bolts with washers at first and later switched to M10 flanged bolts and nuts because the washers were a pain. It's important to note the holes in the struts are significantly larger than the bolts to aid in assembly and to account for any precision issues, non-level ground, etc.
Step 2: Design Your Skeleton
There are many websites that will help you select a dome design, calculate the strut lengths and so on, so I will gloss over that a bit. By far the most thorough and technically apt site I found and used was simplydifferently.org. My only critique of the site for dome-building purposes is the sheer volume and technical detail of the information found there. It might be a little daunting at first. Some other sites I used for reference are:
There are many, many more - google is your friend.
After doing a lot of my own math and reading others' accounts of how best to maximize your material usage, I found that a 23.75 foot diameter dome, built to the 3V formula wasted almost no material if using 10 foot lengths of EMT. Using this formula I needed 575 feet of material total, or about 60 10 foot lengths. At the time I think a 10 foot length of 3/4" EMT was about $3.
A common question at this size is whether to use 1" or 3/4" EMT. I used 3/4 mostly based on cost, and I was very glad that I did when it came time to:
- Flatten the struts, and
- Move the bundles of struts around, as they are already quite heavy.
The 3/4" is strong enough that I can climb all over the dome as long as I grip and step near the vertices (I weigh 200# or so and I've had myself along with another fellow who weighs around 275# on the structure at the same time). This dome has also now seen 5 pilgrimages to Black Rock City and is still in great shape. As such I wouldn't recommend using 1" for anything less than a 24 foot dome.
Step 3: Figure Out Your Canopy
Shown above is my dome with the nearly completed canopy. I will cover how I made it in more detail below; the primary point here is to start thinking about your canopy now. It's a common story to get excited and build the skeleton and then realize the canopy is a whole different animal.
You have options here - many, many options depending on your budget, what you're familiar working with, your desired effect, etc. Some alternatives I considered are:
Tyvek - a DuPont fabric used for envelopes, coveralls, and house wrapping. Tyvek is light and strong and breatheable, but can be expensive. There are many success stories using this material for dome covering.
Shrink Wrap - you can buy polymer shrink wrap designed for overwinter storage of boats. I thought it would be great to make a loosely fitting cover and then heat shrink it to a perfect fit, but it didnt' seem easy to disassemble and reassemble over time, and I was worried the desert heat may deform or damage the plastic.
Tarps - a fellow burner and friend of mine stitched together cheap poly tarps to create his dome cover and it worked out quite well, but it is very noisy in a windstorm.
Canvas - very nice. I would love to have been able to do this and tie dye it, however cost was too much of a factor.
Billboard Tarps - This is what I used. I'll come back to the details later on in this instructable; the selling points were mainly cost, durability, and the fact that the seams can be glued instead of stitched.
Step 4: Procure Your EMT and Cut Your Struts
Home Depot is a great source for this stuff. I didn't have access to one when I made my dome and so I went through an electrical supply wholesaler who was nice enough to sell to me without an account.
IMPORTANT: When figuring out your cut lenghts - you must remember that the strut lengths that most dome calculators will give you is the distance from the mounting hole center at one end to the mounting hole center at the other end. This does not account for the extra material at the end of the strut beyond the mounting hole. For my struts I left 1.5" from the hole center to the end of the cut - meaning each strut was cut 3" longer than the theoretical vertex-to-vertex length calculated by dome formulae.
Pictured are my struts after being cut and having one end flattened
Step 5: Flatten Your Strut Ends
Note: I went a little overboard on the tooling here, making a custom die, and using a 10 ton hydraulic press. I know a fellow that simply hammered them flat (be prepared for some muscle fatigue if doing it this way) another fellow who used a vice (again, we're talking a lot of struts - this will be tiring) and so on.
As I mentioned above, I made a die to slip the strut ends into so that it would create a nice tapered transition to the flat, and then used a hydraulic press I had at work. Even so this was quite a bit of work.
Step 6: Drill Out Your Strut Ends
I'm sorry I don't have photos of this process - I am certain that I took some but I cannot locate them. I made a very simple jig so that I could just put the end of the strut against one block, and the edge of the strut against another and then drill.
CAUTION! Drilling thin metal parts with a large drill bit entails a significant chance of the drill bit catching your material and yanking it out of your hand. I ruined several struts by wrapping them around the drill bit due to this problem. I highly recommend drilling several rounds of pilot holes (1/4 then 3/8 then 1/2), despite the added work, this makes the process smoother, safer, and depending on your machines, it may even be faster.
Tech Note: At this point many guides suggest bending the ends of your struts to 12 degrees to match the curvature of the dome. While this is not a bad idea, I found it to be unnecessary (I actually did this step and then felt dumb for doing it). The thing is, you're going to bend your struts when assembling them - there's really no avoiding it, so spending a bunch of time getting the perfect tab angle on each strut is sort of a waste, but it doesn't hurt anything.
Step 7: Paint Your Struts!
This is actually important!
You now have three varieties of struts that need to be assembled in a specific fashion. Two of these types of struts will be very close to one another in length and not easy to tell apart at a glance. Color coding is very helpful! I recommend painting the strut types to match an assembly image (above image is from simplydifferently.org) to make it easy to assemble the final product.
Step 8: Assemble Your Skeleton
Even if you've done everything right - this is bound to be difficult the first time. If something is not fitting, make sure to double check your assembly diagram. After you have done this a few times, you'll remember the pattern that it goes together in, but at first it is very easy to make mistakes and get frustrated. Having said that, after you have double checked your strut diagram, don't be afraid to use a bit of muscle to push or pull a couple of vertices together. Sometimes this will warp or pull the dome out of shape - this usually means your bottom layer is not sitting in a perfect circle.
Use a helper: not just for making light work, but for holding sections of the incomplete dome up while you go get more struts to put it together. The structure will be very weak at first and you can bend your struts. This isn't usually a big deal as the struts are quite resilient, but it's frustrating. Having a helper is a good idea.
Start at the bottom: This isn't the only way to do it, but it works for me. If you build each layer in full before starting the next, the structure sort of holds itself up as you put it together.
Use a folding table: I find that using a portable folding table works great to hold up sections that want to fall over until you get them tied in, and later in the process the table is a good height to stand on to get the top struts (Please be careful - tables are NOT designed for this, so do this at your own risk).
Hardware: Initially I used 5/16" bolts with washers, before concluding this was an enormous PITA, as you have to deal with washers at every vertex, and inevitably half of them get dropped/lost. After the first year I switched to M10 flange bolts and flange nuts and did away with the annoying washers.
Use Vice Grips: It's extremely awkward to try to assemble ALL of the struts at any given vertex at once. I suggest laying the ground circle and then adding struts as you go around to build up the next layer, then adding struts to that layer and so on. So maybe you'll attach 3 struts together at first, and then add 2 or 3 more to a given vertex as assembly goes on. The thing is, these points are under stress from holding the rest of the structure up, so if you take the nut off to add more struts, it all wants to come apart. The way I deal with this is to put a large set of vice grips on the partially assembled vertex (sorry I don't have pictures of this - may add some later if I ever set it up again). Once you've clamped the vice grips on a joint, you can slide the remaining strut(s) onto the bolt and replace the nut, then remove the vice grips. I don't know how I would do it alone without them.
Use a "Persuader" bar: No matter how fastidious you are about laying things out perfectly, the last few vertices are going to put up a fight. In extreme cases it can be very, very difficult to get the holes to all line up, particularly since I usually do the top vertex last. A trick I discovered is to use a long, thin bar (I use a 3/8" ratchet drive extension with the end ground to a taper). I slide the bar through the holes of the un-cooperative struts, at an angle, with the struts misaligned however they need to be to accomplish this. Once I have all the holes of all the offending struts hooked over the bar, I use it as a lever to pull them all into alignment, and then pull the struts down the bar by hand, fasten vice grips, remove the bar, install the bolt and voila.
Step 9: Cut Out Your Canopy Fabric
As discussed above, you have many options; I chose recycled billboard fabric because it was cheap, mainly, but also I wanted to glue the seams together rather than sewing, and this material can be cemented with solvent cement to form very strong, waterproof seams.
There are also several ways to cut the pattern from flat fabric to form a dome shaped cover. There is the leaf method discussed at length here:
There is the "tennis ball" pattern, which I've never seen implemented personally
I chose to cut hexagons and pentagons out, and then remove a thin slice from each one to create a slightly conical 3D shape to each polygon. I then glued all the polygons together at the edges to end up with a dome shaped cover. To lay this out, I simply used the strut lengths calculated in the beginning to lay out the edges of my polygons; this will naturally leave a slice to cut from each one. You'll see from my sketches above that I was initially going to cut out a triangle to correspond with each "panel" of the dome and then seam them all together, before I realized I could save a LOT of seams by doing the polygon method.
NOTE: At this point it's important to note that I designed my canopy to hang from the INSIDE of the structure, so I made my polygons about 1% smaller than the strut lengths I used. You will need to make a similar adjustment in the other direction if you're making a cover for the outside of the dome.
Make sureto leave enough material to overlap your seams - if you just cut the pieces to size with no seam allowance, your cover will come out way too small! I overlapped each seam by about 3" for maximum strength.
Step 10: Seam Your Canopy Together
Billboard fabric is a fiber reinforced PVC material like what's used in inflatable rafts. There is a product called HH-66 which is a solvent cement designed for cementing this kind of material together. It's relatively easy to come by in the USA, but was not available to me when I made this canopy (I lived in Northern British Columbia at the time). Instead I found that glue from the hardware store designed for gluing vinyl shower liners and pond liners together worked well. I do not unfortunately remember the name, but any sufficiently salty veteran of plumbing and home construction at the hardware store should be able to help you.
The amount of work required in this step cannot be understated. This was a BIG job to do alone, and it took me nearly a month worth of weekends.
I overlapped each seam by about 3" for maximum strength.
At each vertex, I laminated a 6" circle of fabric for reinforcement, as the canopy would hang from the vertices.
Step 11: Make Canopy Hangers
To hang the canopy, I put a 5/8" Grommet (available from McMaster-Carr) at each vertex, and pushed through a loop of heavy duty nylon bungee cord to fasten to the skeleton.
To make the hangers, I bought a bunch of cheap plastic cutting boards from the dollar store, and used a hole saw to cut out 2" plastic washers, then enlarged the center hole to 1/2". These fat plastic "washers" were just to spread the load out a little bit as I was concerned about a simple knot being too small and pulling through the fabric.
Then, I cut 12" long sections of heavy duty 5/16" nylon reinforced bungee cord, looped them in half and tied a knot so there was about a 3" loop, and then cut off any extra, and put some hot glue on the knot for good measure.
Step 12: Hang Your Canopy!
For the first 2 years I used zip-ties to fasten the bungee loops to the skeleton, and eventually got smart and bought a bunch of aluminum carabiners, so now I can loop the bungee over the vertex and snap the carabiner back over the stretched out bungee. Every year I lose/break a few but they are dirt cheap.
To Fasten the dome around the bottom, I tuck the flaps under the skeleton bottom. There are more grommets installed in these bottom flaps, from which I run miscellaneous bungee cords to the rest of the dome skeleton. It's not very pretty but it works very well.
You can see from one of the above photos that I also installed a zippered window - this is highly advisable, as a plastic dome in the desert in the summer is basically a super greenhouse unless you have windows.
Step 13: Add a Door
Domes commonly just use the open triangles as entrances and exits, but I wanted to be able to walk in and out upright and bring my trike in and out and so on, so I used some 1" EMT to make two larger struts as shown, forming a door. To each side of the door there is a short ~18" long strut bracing the long struts to the nearest vertex. This may or may not be necessary but It certainly makes me feel better when I'm climbing on the structure.
For the canopy, I just sewed a heavy duty zipper where the door is in the skeleton, and carefully sliced the vinyl fabric into a flap. This door actually does not work very well, as the desert dust clogs up the zipper, and the whole canopy is under tension from the bungees. In later years I just installed 6 eyelets with bungees and carabiners to close the door. It's not wind or water proof, but it really doesn't need to be.
Step 14: Stake It Down!
This is very important. This dome is a 500lb sail in a windstorm; I watched it move 20ft across my back yard before I staked it down. For this I used 2 foot long rebar stakes made by bending 5/8" rebar and welding a reinforcement to the bent section to help cope with the hammering in and pulling out.
Step 15: Enhancement #1 Add a Bedroom!
In 2012 I got a utility trailer with which to haul all my stuff out to the desert, and I thought it would be a great idea to incorporate it into the structure! This has several advantages, not the least of which is giving me a solid little shelter to sleep in.
The trailer provides some structural support during setup which is nice. It's also currently equipped with solar panels/batteries that run an inverter, phone chargers, interior and exterior lighting, a swamp cooler, etc.
Step 16: Enhancement #2 - Add an Awning!
In 2013 I went with a group of people that wanted to have a communal shade area, so I made an awning from more billboard fabric, rope and some 1" EMT poles.
Step 17: Get Photographed From Space!
This dome has happened to star in several Google Earth photos, which I find nerdily amusing - especially the one in my backyard!
Step 18: Never Stop Adding Features
Since I made it, this dome has been upgraded (and re-downgraded in some cases) with several features, including
Interior Lighting from the trailer
Upper platform on top (downgraded before I ever went to the desert - too sketchy)
Steel feet with holes for lag-bolts
Lag bolt stakes instead of rebar, to save my back.
Interior hammock hangers
We have a be nice policy.
Please be positive and constructive.
Wondering what pipe size would be strong enough to build a 30'tall 70'dia 5v dome, we are considering using 1.25" emt conduit. Would that be sufficent? Any resources on the web I can link to? Much Appreciated!
For a project that size I'd strongly recommend doing a LOT of research and maybe going to check out some desert domes at events or going to one of the places that rents them out to see how they are built. Even at 5V you're going to have some 9+ foot struts, and the potential for any single strut to bend when stepped on (or buckle under distributed load) goes up approximately proportionally with the square of length. The wind load goes up with the cube of height, and the structure weight goes up with the square of the dome radius... basically what I'm saying is you're talking about building a very serious structure with some big forces involved and the potential for people to get badly hurt if it goes wrong. Please consider your material choice carefully and extend your research way beyond instructables. If you know a structural engineer I would highly recommend buying him or her some beers and asking for help.