With the lower building mostly complete and the backfilling well underway, we can finally start assembling the the dome structure. While we were confident that we could pull of this build, we were a bit apprehensive going into it considering our first dome failure. We were comforted by the fact that we could make the necessary adjustments with our piped hubs if we ran into a a similar situation this time around.
Getting Started
We started by only connecting the steel base hubs. We were still unsure how we would marry the dome to the lower building and we knew that these base hubs would not be lying flat, but angled inward. Maintaining this angle is going to be important making sure every strut will line up where it’s suppose to.
Attaching the dome
We decided to put a base board under each base hub and use lag bolts to loosely attach the back side of hubs. The base boards are screwed into the bottom floor joists to secure the dome to the base building.
We then put another lag bolt under the inside of each hub that we could use to raise or lower each hub. That way when we reached a point where a strut didn’t fit quite right, we could turn the bolts up or down to realign the structure.
Tying it all together
When we were looking into the different ways to design the hubs, one of the main issues about using pipes and strapping is finding a good way to get the straps tight and prevent any wobbling. General consensus was that you needed some sort of strap pulling tool, but we decided to try a different idea.
If you look closely, you’ll see that the hubs are actually 1″ longer than the face of the struts. This was intentional and creates a point where we can add a final screw close to the hub to cinch the strap down.
Finishing up
It took around a week grabbing a few hours after work to fully assemble the structure. Adam did a great job cutting out all the struts and making sure they were all exactly the same. He’s been really good at setting up the jigs necessary to get these pieces right.
We also remembered an important point for assembling the dome. We only put one screw on the inside of the band and kept each hub loosely attached until we had every strut up. This allowed us to rock and squeeze the dome into the correct shape. We then added the rest of the screws and tightened each strap from the bottom up and the gaps we did have at the top closed by the time we were done.
Other than having to figure out the base attachment, this part of the built went pretty smooth. We’re super happy we went with a piped hub design because it was so simple to cut the struts and assemble. After we tightened everything up, we added two steel U-brackets to each base hub to make sure the dome wasn’t going to go anywhere.
Edit 7/15/2020 – I’ve received a lot of messages regarding a closer look at how the hubs were fabricated and how they work. I made a quick mock up below which provides a bit more detail.
Materials
- Steel Strapping – Order from ULINE.
- Schedule 80 pvc – Purchase from any plumbing supply (might have to special order).
- Schedule 40 steel pipe – Purchase from any hydraulic/welding shop.
Notes: The steel pipe might not be necessary if you put more thought than I did into how you anchor it to your base/ground.
This is inspirational. I’ve been wanting to build a dome for a long time but this is the first time it’s seemed doable. I bought 24 feet of schedule 40 steel pipe and I’m cutting it into hubs at my friend’s metal studio. Did you cut your 2x4s at an angle to fit them better against the hubs? The site I’m looking at says 78.1, 78.4, and 80 degrees. Does that sound right? Thanks for putting this page together.
Hey thanks for the kind words! Yea using the hubs made it sooo much more straight forward. Yes, you should set up some sort of jig to cut the angles in the 2×4’s because it’s super important that the struts are identical. Those angles seem right, but I’m not sure what site you’re using. If you want more assurance I explained my design process here https://upnorthaquaponics.com/2019/03/05/the-design-process-the-dome-structure/ using this tool https://acidome.ru/lab/calc/#Flat_7/12_Piped_D100_3V_R6_beams_88.9×38.1. Let me know if you want to hash out further details and thanks for the interest!
Thanks for the offer, I’d like that. How did you waterproof the hubs where multiple glazing panels join?
I cut some pvc trim pieces to fit and siliconed/screwed it down and I also siliconed from the inside as well. It turned out ok. I think if I were to do the roof again I would have just used aluminum flashing and siliconed/screwed in place for more flush ridge caps.
FYI- Don’t use any petroleum based products like butyl rubber or roofing tar. Polycarbonate has awesome durability, but has shit oil/chemical resistance. It will damage the plastic and won’t bond properly so it will still leak.