A nifty way to build modular multi story structures
All files (.skp) are created with Sketchup, but I have also provided DXF (line NOT mesh) files for easy import into other CAD Software.
We have been using 18mm (3/4") marine grade baltic birch plywood (and I recommend you do too, because I have tried to use cheaper stuff and it's not strong enough and also can't be cut with low enough tolerance). Therefore all designs assume 3/4" material.
The holes are used to hook in the ratchet straps needed to get the diagonal cross tension that keeps the structure together.
The reason the sheets are sized 11.5in is to maximize the amount we can cut out of a 4x8ft plywood sheet (the 1/4" drill bit eats the margins).
The node sheet dxf files are ready to be sent over to your fabricator of choice. I recommend letting them know that the sheets are meant to be slid together so that they get the machine set up with the right tolerance. You will need a 1/4" diameter drill bit or otherwise you will have to modify the files.
6x 3/4in thick node sheets are required to assemble one node.
Since you won't be needing all holes on a node for structural purposes you can use the other to run cables, attach fabric, flag poles, etc.
Nodes also make for amazing cup holders btw.
2x 3/4in thick subfloors with each 2x 2x4 joists are required for one floor.
Mind you that the floors are not up to construction code! Thankfully plywood is amazing material and they are good enough for a temporary structure with lots of people on them dancing and doing other shenanigans. I am considering either using 4x4 for the joists next time or adding a 3rd 2x4 joist... there are trade offs though.
We used construction grade plywood for the floors from HomeDepot.
With 8x nodes and 12x 4x4 7'7" lumber pieces one can put together a düxel (dust voxel).
You will need ratchet straps to get the diagonal cross tention that keeps the structure together. We used these 14ft ones with a working load limit of 3,333lbs.
I single düxel requires about 8x straps depeding on how stiff you need the structure to be. Larger structures usually can do with less. We calculated 1.75 per node to estimate the amount for our structure (You will need more straps during setup than for the finished structure though).
I designed the subfloors so that they can be efficently stacked with the lumber in between.
We have designed a couple additional components for this system
In 2019 we also decided to build some 24ft ceiling beams to have a larger roof. This is typically very straight forward but we had two extra requirements a) fitting them into our 20' shipping containers and b) them being strong enough for aerial acrobatics. As such we cam up with the following design that has a breaking strength of 5000lbs at center.
The ends of the joists have holes in them in the right size and position to match the ones of the nodes. This is to be able to secure them additionally to the ratchet straps...which seemed reasonable given their size. We used simple stage safety steel wire loops to do so.
Stage truss mounts
Also In 2019 we used real stage Par lights for the first time and needed a way to mount them to the structure. We decided to mount them in clusters via stage truss pipes that are connected to the nodes with standard swivel clamps which worked really great. For heavier gear its also possible to use two swivels on each end.
The pipe we used is actually just 8ft long, 2in diameter conduit pipe from the hardware store...and the swivels we used are these 2in clamps ones.
Additionally to clamping we used 2 safety steel wires per pipe that was connected to the pipe via standard eye hook clamps.
There is no CAD files for this but we have a collection of photos that show the different mounting options
- Practice Setup! Don't just willy nilly show up on the playa and try to wing it
- Tools: a level, multiple (step)ladders, work gloves, rubber mallets, a crow bar and maybe an actual mallet (for when shit went wrong)
- You will need a flat and stable ground, specially for larger/multi-level structures
- Use kiln dried lumber for the 4x4 to avoid warping and cracks (otherwise its going to be a one time only project)
- Build the first düxel first and make sure its 100% level... otherwise you are going to multiply the mess
- Only have 3-4 people working on putting the structure together at a time... the others can deliver materials
- Put the subfloors in before you tighten it
- Deciding where and where not to put ratchets is an art on itself...better find someone who knows what she is doing!
- The structure will takes 2-3 days to settle...so you need to keep tightening the ratchets every day
- To build the hotel structure you see on the photo it took about 12 people 2 days to completly set it up (incl fabrics, lights, etc) and 20 people about 2h for teardown and packing (under playa conditions)
- It's düxel not duxel... because umlauts :)
Please feel free to reach out if you have questions...and send photos of your düxel projects!
- Create metric versions of the designs so that people outside of the US can use it
- Improve the subfloors
- Ratchets need to be keep fastened every day, I wonder if there is a better fastener
- Explore using cheaper materials
Q: What are the support beams for the second story floor? and how are they attached?
A: These subfloor are built with construction grade 8x4 plywood, and 2x4 beams to support. We built a jig to make a bunch of them with the correct measurements detailed in the design.
Q: What are the weight and movement restrictions per 8'x8' cube?
A: First of all, this system is not up to code and we will be in no way liable for what happens!
Now that we got that out of the way: It’s a temporary structure and most of the engineering assumed that.
Practically speaking we have had probably up to 20 people dancing on a single duxel without issues (more people will hardly fit on a 8x8ft space).
I am sure if somebody big enough tried and took a huge hard jump in the center of the floor it would snap...but it’s unlikely to collapse or break through....simple because plywood is hell of a material. There is also always two more ratchets diagonally under each floor.
The only damage we ever had was some screws getting pulled through the plywood on the edges...this was in part because they were drilled in too deep and part because that’s the weakest part. We use washers now and it hasn’t been an issue.
Now about the theory: The beams we use are 7’ 7” 4x4 kiln dried Douglas fir lumber. If memory serves well each of those beams can carry 10,000lbs vertically so a single duxel can carry 40,000lbs (evenly distributed). So it’s unlikely that the vertical beams will be the bottleneck. That said if you wanna go really high or do other crazy stuff you can easily double/triple up the vertical beams (we will be doing so this year for a aerial acrobatics setup).
Now to the horizontal 4x4s, those can take about 4000lbs at center...again evenly distributed that’s 16000lbs. It’s actually a bit stronger because you got another 3/4in plywood layer on top.
Now to the nodes, the ones we made are 3/4in marine grade Baltic birch ply...plywood can withstand about 4000-5000 psi of compression. The 4x4 beams are actually 3.5x3.5in so they actual surface is 12.25 square inch...means it can withstand up to 49,000-61,250lbs! The holes for the ratchet straps can hold up to 10,000lbs each...so it's unlikely to rip them out when tigthening the ratchet straps too much (the ones we use are rated 4000lbs)...and we have never achieved to rip one out.
Now a word of caution, we tried to use cheaper ply for the nodes and actually managed to rip out a hole with a ratchet so don’t cheap out here!
Given that losing a hole is a possibility I always ensure 2x/3x safety when we build structures by using two straps per diagonal or having a duxel right or left which has another diagonal ratchet.
Q: Could the subfloor be done away with and the 4x4 go directly to the ground with respect for butting it into a wider pad perhaps 1'x1'? Any ideas about how the posts could be stabilized against by the diagonal forces from the straps... perhaps adjacently placed large screws in the ground with some for of connecting tie to the post?
A: In general we do not recommend this, as the structure is meant to be symmetrical and held together with tension by the ratchet straps. As you pointed out, if you get rid of the base structure (4 nodes, and connecting 4x4 beams), you have to do a lot of work to stabilize it. Not sure why you would want to do this - cost? lowering the floor?
Q: What is the cost per cube approx., I'm assuming subfloor + 4 posts + straps - not including roofs?
A: Roughly $750 for a standalone cube, but decreases when you are able to reuse nodes
8x nodes * $62/node = 496 12x 4x4 beams * $10/beam = 120 2x 8x4 3/4" ply * $15/ply = 30 4x 8' 2x4 * $6 ea = 24 6x industrial cargo ratchet straps * $12/strap = 72
This would not include roofs, and you can strengthen the cube by adding 2 more straps.
- We get our nodes CNC machined by Rob at Lucid Machine Art
- We use 2in wide, 14ft long ratchet straps from Cargo Equipment Corp
- Gregg Fleishman on who's patent this all is based on
- The Lost Hotel for pioneering this idea
- All the amazing souls at Hotel California for making this happen
- Douglas Waters for helping me picking the right type of lumber (and where to get it without breaking the bank)
- Stephanie for teaching me how to use a CNC machine and giving me a lesson on wood types
- Rob Ehret who was right about using baltic birch marine grade plywood from the beginning and letting us use his shop
- Slawek Krause for reaffirming that this would probably work :)
- Jenny Guan for adding the umlaut :)
Copyright (c) 2016-2019 Matthias Wagner
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